The figures show the coldest temperature (degrees F) endured at each city over this past weekend (28-29 Jan). The pattern that jumped out at me is the “warm” Fairbanks surrounded by a bunch of colder towns and villages. Now, I’m not about to make any conclusions based on this one case, but stay with me and I think I can make some sense of this, at least to whet the appetite for further study. About the map–you might point out the Nenana was not much colder than Fairbanks, and after all, some places are just colder than others. To check that idea, I’ve tabulated the long term averages for the stations on the map (some did not have enough data, so I’ve added Hughes to stand in for Huslia, and I also added McGrath for reasons which will become apparent).

The stations are arranged with the coldest average at the top. There is not a lot of correlation between the average temperature in the coldest part of the winter (the table) and the Jan 28-29 cold snap minimums (the map). Fairbanks is only a little warmer than Nenana on this chart, based on WRCC period of record data, but is slightly colder according to the NCDC’s latest (1981-2010) normals. This apparent inconsistency is probably due to the many holes in Nenana’s temperature record, and shows how careful one must be when working with climate data. Anyway, the map is more of a conversation starter than anything. We need more data. Complete, reliable weather records going back far enough to see long term trends are quite hard to come by in Alaska. The best data for this little investigation is a comparison between Fairbanks and McGrath. McGrath is a ways from Fairbanks, about 275 miles (440 km) actually, but for this purpose, having complete, quality data was paramount. There are stations much closer geographically but with less complete and in some cases less reliable data. Those stations also support what I’m trying to say about Fairbanks cold snaps. Click here to see them. What am I trying to say? This graph of the two 1st order stations says it:

click for a larger version

The columns on this graph show the number of days during the given winter that the temperature dropped to –50 F (-45.5 C) or colder, red for Fairbanks, blue for McGrath. The jerky lines above are temperature observations for each station (same colors), showing the average of daily lows for December, January and February for the given winter (December of the year previous to the label). The average lows track as you would expect: each of the two stations follow the ups and downs of the 70 winters in fairly close agreement to each other, or with Fairbanks being a few degrees cooler. The number of –50 or colder days is fairly close as well, through about 1971. In fact up till then Fairbanks has more of the super cold days than McGrath, but that’s nothing unusual since Fairbanks is colder on average–the line graph clearly shows that–and in the winters that Fairbanks had significantly more –50 days (1965 & 1969) their DJF average was significantly lower as well. What begs an explanation is the lack of –50 days after 1971. There is no change in the relative DJF temperatures (almost all the –50 days occur during those three months). Yet from 1971 onward, McGrath has had many more 50 below days than Fairbanks, even while their average temperatures have been very close to or a bit warmer than Fairbanks. In fact, the rate of occurrence of days 50 below or colder does not change much for McGrath or the 4 other interior stations you can see in the supplemental file, but at Fairbanks it drops by 4/5ths!

Alaskan “heat” islands

I think we are dealing with an interesting variation of the Urban Heat Island effect. The UHI effect is the well-known and well-documented rise in temperature of a large urban area as compared to surrounding non-urban areas. In more temperate areas the UHI is only significant for large urban areas, and has mostly to due with radiational effects due to changes in the nature of the land surface. In Alaska we don’t have the kind of urban-ness needed for a significant UHI effect based on the mechanism just mentioned. Even Anchorage, as large as it is, has so many trees, and indeed large blocks of natural forest areas within the city as to mitigate those effects. Apart from Anchorage, no city has the size that would create a significant UHI in the lower 48. But we do things differently in Alaska, as the saying goes. Radiational effects may be small, but emissions of sensible heat, and especially water vapor and particulate matter are what I believe create UHIs in Alaska. Winter low temperatures show a much stronger effect. Even then, the UHI effect for Fairbanks appears to be fairly weak. If it were strong, my graph above might show some divergent trend over the years of population growth of Fairbanks vs McGrath (see graph below), but it sure doesn’t. A study at UAF (Magee, et. al. 1999) looking for a possible UHI for Fairbanks found about a 1°C (1.8°F) warming of winter lows compared to nearby Eielson AFB. It’s just one study of climate records, which as mentioned above, are not always as complete or precise enough to draw too many conclusions. (An actual field experiment in Barrow found a much larger UHI effect, surprising to me given that Barrow is not only much smaller, but also much windier. Winds tend to homogenize the air and wipe out small scale temperature differences. click here to read the study.)

Why would the UHI effect be so evident for extremely low temperatures when it is fairly weakly reflected in average low temperatures ? Several factor present at average low temperatures are sharply increased in the extreme cold.

1. During cold snaps, temperature Inversions are sharper and winds tend to be lighter, meaning local effects are not diluted as much by mixing with surrounding air.
2. The colder it get, the more energy must be used to heat buildings, keep cars running, etc., and so the more waste heat enters the atmosphere.
3. The more fossil fuel consumed, the more water vapor and particulates enter the atmosphere, releasing latent heat though condensation, freezing and deposition.

This last item is crucial, but might need some more explanation. When carbon based fuels are burned, the primary byproducts are carbon dioxide and water vapor. There is a lot of energy in water vapor, a potential kind of energy called latent heat. This is an important lesson in Meteorology 101. The latent heat is put there by the sun when it evaporates water, or, in this case, by the heat of combustion. There is very little water vapor in the frigid winter air of uninhabited interior Alaska (almost none) since there is so little heat available to convert or keep the H2O in vapor form. Of course there is very little liquid water to be found lying around either, for the same reason…not enough heat to keep molecules moving enough to stay liquid. But in a city the size of Fairbanks, with water vapor flowing out of every smoke stack, power plant, furnace flue, exhaust pipe and jet engine, there is quite a bit, and it does not want to stay gaseous long. At moderately cold temperatures (+10F down to around 25 or 30 below 0F)  it often makes liquid water fog, which often gets mixed into drier air and turns back to vapor, or become rime or frost on solid objects. Sometimes, if the right kind of particulates are at hand, (remember how burning fossil fuels releases particulates: smoke, etc.) it can form ice crystals in the air which gives us those brilliant halo and sun dog displays. All these instances of water changing to a lower energy state release heat. And when fog or clouds are formed, the fog or clouds can also retard heat loss due to radiational cooling of the ground. But often it keeps getting colder despite these effects.

Alaskan cold

So, the colder it gets, the more moisture is put into the air by humans trying to keep warm or keep their vehicle or aircraft engines running, but the less moisture the air can keep in vapor form. Around –40 (F or C) and colder the liquid and gas phases are basically no longer available to H2O. It’s getting squeezed out of the air as fast as it can be put in, and the result is usually ice fog. And lots of latent heat, since there are two phase changes to get to the solid ice particles that make up ice fog. So let’s look at the recent cold snap and see the difference in moisture issues between Fairbanks and much smaller, but usually warmer, McGrath. Last graph, I promise.

Look especially at the temperature changes. In Fairbanks, when it dropped below about –45 F, the visibility dropped to 1/2 mile, then 1/4 mile or less…ice fog. With the fog thick and constant for the next day and a half, the temperature did not get much colder—nor warmer. In McGrath, the visibility only dropped for short periods and not as drastically as Fairbanks, despite even colder temperatures at the low end. There was less water vapor being put into the air, less fog, and less latent heat release and less to hinder radiational cooling. During the afternoons, the lack of fog allowed some warming due to a little sunlight, though on the 29th it looks like the warming was due to other reasons.

If your fingers and keyboard are not too stiff from the cold, type in your comments or questions below. I’d love to hear your thoughts.

You probably know that where the isobars are drawn with the closest spacing is where the gradient is the strongest and therefore where the wind is supposed to be the strongest. So although most of the state should be somewhat windy, SE AK and on north to Cook Inlet should be especially so. Indeed, here is how the Inside Passage looked like at Haines this afternoon:

The interesting thing is that although this extremely large weather system looks fairly simple on the map—nice smooth isobars defining areas of greater and lesser pressure gradient and, presumably, wind strength—the terrain creates a detailed, small-scale patchwork of wind speeds and directions that even some meteorologists have had trouble believing at first. Let’s look closer at the above photo and situation. On the right end of the dock is a wind sock…stretched out horizontally (click on the photo for a larger view). No surprise, the wind was pretty strong there, perhaps 20-25 kts (knots…1 kt = 1.15 mph or .5 m/s) but less, maybe 10-15 kts where I was standing. But look out in the middle of Lynn Canal, or to be more precise, the far 1/3 of the Canal. See what looks like a thin layer of fog? It’s blowing spray…the winds out there are probably a steady 45-50 kts with gusts to 60 or 65 kts. This is not just an exaggerated guess. At the Skagway airport, about 13 miles north (to the left in the photo) the instruments were (and still are as I write this) reporting sustained 35 kts with gusts to 45-50. About the same distance to the south is Eldred Rock where the lighthouse winds are averaging 55 kts sustained, gusts to 70-81 as you can see from the graph below. The state ferry trying to make its rounds to Skagway and Haines today turned around half way and headed back to Juneau.

–graph from the National Data Buoy Center–

Link directly to the Eldred Pock page at NDBC

What’s at work here is channeling. When mountainous terrain has gaps, valleys or channels, which of course it usually does, the wind can flow through those channels to get to the other side, and that flow is often accelerated compared to what it would otherwise be. The wind “wants” to flow through these gaps when there is a difference in pressure between the two sides, which of course there usually is. Here are some rules about channeled winds:

1. The more stable the atmosphere is, the stronger the channeling effect
2. The narrower the channel, the stronger the channeling effect
3. The wind tends to blow along the channel, not across it
4. The wind blows from the end of the channel with higher pressure toward the end with the lower pressure
5. The greater the pressure difference from one end to the other, the stronger the wind
6. The wind is accelerated through, and for a distance downwind of, the channel, but is often light upwind of the channel

Now look a the map of Lynn Canal:

View Larger Map

You can see the extreme channeling leading to these extreme winds. 80 kts is not unusual for Eldred Rock (A on the map).

What about the direction? Look again at the surface pressure pattern, shown cropped and blown up below, Eldred Rock is at A, approximately. From which direction should the wind blow?

Most weather books for the layman, and even many more advanced textbooks would tell you something like this: “The wind blows counterclockwise around the low (N hemisphere) parallel or angled 20-30 degrees across the isobars toward the low.” With this instruction, the wind at “A” ought to be blowing from the east. In fact it is blowing from the north, about 340 degrees true. Many protest and say “the wind can’t circulate clockwise around the low!” Re-read points 3 and 4 in the channeled rules above and look again at the Google map. The channel is oriented right along 340-160 true…just a tad counterclockwise from north-south. Look at the pressure pattern. The pressure is definitely higher to the north, so the wind blows from north to south, right along the channel.

If it makes you feel better, the wind at “B”, the Fairweather buoy, is blowing from the east southeast, at 40 kts gusting to 50. Over the open ocean the coriolis effect is at play and the textbook answer works. Over highly blocking terrain, the coriolis effect is not at play because the air is initially not (hardly) moving, having been blocked by the mountains (it does not want to go over since the air is so stable…rule 1 above). When the air finds a gap or channel, it races through, more directly from high to low pressure. The coriolis effect does not have the time to “turn the wind to the right,” nor can the wind turn to the right since it is constrained in narrow channel of solid mountain! Don’t throw out the textbook, just add some notes in the margin. Few of them acknowledge this exception to the wind direction rules…maybe because most authors and publisher hail from the flatter east coast.

Skagway is in the same channel as Eldred Rock, but the speeds are a little less since the wind is coming off the land and the land has more friction than the water. In the summer, with predominately south winds, there is less difference in speed between Eldred Rock and Skagway. What about Haines? The wind at the Haines airport has been averaging about 5 knots during this event. Why? Look a the map. The Haines airport is a couple miles west of the dot labeled Haines. It’s in the Chilkat Valley, oriented more Northwest-Southeast than north-south Lynn Canal. In this case the isobars hardly cross it–they are pretty much parallel to the channel, so there is little difference in pressure from one end to the other. See rules 4 and 5 above. [If the low were farther east, say over Ketchikan or BC, The wind would blow faster down the Chilkat Valley, and when this happens it often looks on the large scale map like the wind is blowing exactly clockwise around the low, 180 degrees from the textbook solution!] Certainly other parts of Haines, downtown in particular, have more wind than the airport in the current situation, because of their exposure to the edge of the Lynn Canal wind or a wind coming down a smaller side channel. Also, occasional bursts of wind spill over the ridge along the north side of the valley, violating rule 3 above. No absolutes in the weather business.

Now, if the previous material makes any sense at all, get ready for an even more tricky and interesting case. Look up the coast at location “C” on the surface pressure map. The flatlander textbooks would say the wind should be from the northeast, right? Well, by now you know it can’t be right, but you will probably be surprised by this map:

Do the wind speeds and directions look almost random to you? [don’t know how to read the wind symbols? Think of them as arrows, with the point placed on the weather station, the shaft aligned with the wind direction (with the arrow pointing with the wind), and the fletching (called barbs) showing the wind speed: 10 knots for each full barb and 5 knots for each 1/2 barb. Look at Talkeetna for example, the station furthest NW on this map. The wind there is from the north-northeast at 25 knots.] These wind reports are real and they are from the same time as the pressure map above. If you look closely, you will see that almost all the stations with the strongest winds are in, or just at the exit of, a pass, gap or other sort of terrain channel. Most of those have north or northeast wind since those channels will interact best with the large scale pressure pattern as shown on the pressure map above.

The standout exception is Whittier, which has 35 kts from the southwest. Whittier is at location “C” on the pressure map, and it looks like it is not only violating the textbook wind rules but also my channeled wind rules too! What you need to know is that this particular pressure map is too general and smooth to handle this case (other models are more detailed and do show some of these small scale effects). The pressure patterns are affected by the terrain, which in turn gives rise to more possibilities for crazy looking wind directions. In this case the wind is blocked by the substantial barrier of the Kenai and Chugach Mountains and this blockage builds up the air on the west and north sides, the upwind side. This is the higher pressure side to begin with, but the blocking increases the pressure difference, setting up a situation for accelerated gap winds. This damming effect also allows the high pressure to “bend” around the obstacle. For instance, from the pressure map you might conclude that the pressure at Kenai should be about the same as at Whittier, when, in fact, it is a fair amount higher. This bending allows almost any break or gap to be an outlet to the pressurized air, no matter the direction. So the wind at Whittier blows from the southwest whenever there is a low pressure area to the east, southeast or even a fair ways into the south quadrant. Notice the small circle just to the west of Whittier? That is Portage Glacier Visitor Center, a weather station only 9 miles from Whittier as the crow flies, yet so different weatherwise. The wind there is calm. Remember rule 6. There are several other examples of this and the other rules on this map. Can you spot them?

I’d love to hear your questions, comments, etc on this, or other Alaska Weather topics. Click the comments link.

But first, what is a La Nina, how does it affect our weather, and can it really allow one to make a five month or longer forecast? Very briefly, a La Nina is one phase of a oscillating weather pattern in the equatorial Pacific involving air pressure patterns, winds and sea water temperatures. That a weather pattern roughly 4,000 miles (6,000 km) away can affect Alaska’s weather shows the large, interconnected nature of Pacific weather and climate systems and how important ocean temperatures are to them. The tropical part of this system has been studied for decades and is termed the El Nino/Southern Oscillation, or ENSO for short. La Nina is the cool phase of this tropical system, El Nino the warm phase. It oscillates between the two famous kids on a more or less yearly basis, typically with a lull during the northern hemisphere summer and an intensification in fall and through the winter. Many years the phenomenon is weak or noncommittal…a neutral phase. Here’s a intuitive graph from the NOAA’s Earth Systems Research Lab:

For more information on the the ENSO see the links at the end of the post.

As for what it means for Alaska’s winters, the highly simplified version is that El Nino winters are more often warmer, La Nina more often colder. In the following charts I’ve plotted the average temperature from November through March vs the seasonal snowfall total for four hopefully representative locations. This kind of X-Y scatter plot can tell you how winter temperature and snowfall correlate. Each diamond represents one winter of the 62 plotted since the winter of 1949-50. From the scales you can see that winters that fall much to the upper left were cold and snowy, lower left cold & not so snowy, upper right warm & snowy, lower right warm & not so snowy. Near the center winters were close to average. In addition, and pertinent to this topic, I’ve colored the diamonds according to the ENSO phase for that winter: red for El Nina (14 of the 62), blue for La Nina (16) and gray for neutral (32). The lime green circles indicate the “double dip” La Nina winters. Keep in mind that there are quite a few ways to quantify and define El Nino/La Nina/neutral years and which criteria are used could affect this sort of analysis to some degree. My source seems to leave more winters in the neutral bin than some, possibly understating some relationships.

Starting from the north, here’s Nome and Fairbanks (please click for a better look):

Both Nome and Fairbanks show little correlation between winter snowfall and overall winter temperature. At this latitude I would have expected warmer winters to have more snow and colder ones less. Possibly if we considered the water equivalent of the snow it would show up. A little farther north I’m sure the correlation would be obvious. But that’s not the thrust of this article. It’s how the ENSO plays out for our winters. So look at the colors. Both cities show strong evidence to support the warm El Nino, cold La Nina pattern. In both cities only 2 of 16 La Nina winters were warmer than average by any significant amount (one of Nome’s was last winter) and those only moderately warmer. Some of the La Nina winters were only slightly cold but the majority were roughly 3-6 degrees F (1.7-3.3 C) colder than the 62 year average. That amount of deviation makes a big difference over a winter. Snowfall shows no conclusive pattern in these two cases. Neutral years are scattered fairly uniformly throughout the graph for both temperature and snowfall. Interestingly, most of the very snowy years in Fairbanks were neutral years. Perhaps a Goldilocks situation. By the way, the double-dip La Nina years don’t show anything conclusive. There are only four, and they are spread fairly evenly through the La Nina years. Perhaps if the analysis went went further back more could be gleaned. Also, as mentioned above, the criterion used for categorizing La Ninas is not standardized. The Climate Prediction Center calls the winter of 1950-51 a La Nina (a pretty strong one too, so I don’t know why the FSU ranking I used does not). It was, for three of the four cities (all but Nome), one of the four coldest winters of the 62, and it was a double dipper to boot.

For more southerly climes, let’s look at Anchorage and Juneau:

A major difference from the two northern stations is the inverse relationship between temperature and snowfall that is evident at Anchorage, and strong at Juneau. In other words, warmer winters have less snow, colder ones more. This relationship is expected in temperate areas. With respect to the ENSO phase, La Nina winters tended to be colder at both locations, and to a lesser degree snowier. A strong exception is the double- dip La Nina winter of 1999-2000 when in Juneau it was 3.9 degrees F (2.2 C) warmer than average with 44% of average snowfall. At the other three station that particular winter also did not follow the pattern but was not so extreme: Temperatures near average and snowfall near, to above average. Again the double-dip winters do not tell us anything definitive. One thing skiers can be pretty happy about is that there were no La Nina winters in the last 62 years that were both above average in temperature and below average in snow in Anchorage or Nome and only one in Fairbanks and two in Juneau. Study these graphs more and I’ll bet you can tease out more revealing details about our winters.

Useful for seasonal forecast?

What can be deduced from this data to make a projection for the coming winter? With a moderate to strong La Nina already under way, I think we can expect most of Alaska to have a colder than average winter. Snowfall in Southeast is likely to be higher than average but for the rest of Alaska it is indeterminate. If temperatures are not significantly colder, then near average is the likely result—a significantly warmer than usual winter has little statistical chance of happening in a La Nina year. The idea of a double dip La Nina bears further study before I’d want to say much. Let’s just say it will likely be a cold winter for most of Alaska, and I would not be surprised if if it is not much colder than the long term average in many parts.

Backup

Lest you think I’m something special for making a 5-month forecast, I’m not alone, and I’m not going against the crowd. To see more of the consensus, follow these links to the Climate Prediction Center or Juneau Forecast office’s summary. The CPC’s maps are right there on the home page and are easy to use. For more maps click on 30-day or 90-day outlooks below the home page maps. All the winter 2011-2012 maps you can find will say the same thing: confidently colder than average for the southern 2/3rds of Alaska. These are updated around the 20th of each month but I would not expect any change in the basic idea.

Caveats

It is important to note that the above forecast could prove to be flat out wrong, and likely it will be for some parts of Alaska. Alaska is so big that the chances of every part of it being colder than average are pretty low. In particular, the far north and far west (not really covered in our graphs), i.e.  Barrow, and the western Aleutians, seem to often be exceptions. The strong warming in Barrow recorded since about the mid 70s seems to defy trends and drivers that effect other areas. More study needs to be done, but possible reasons are decreases in extend and thickness of the ice pack, and the urban heat island effect (artificially warming the local populated area only). The latter effect has been well documented in Barrow by Dr. Ken Hinke of Univ. of Cincinnati using in situ measurements.

Even if the winter is colder than average, day-to-day and even week-to-week winter temperatures are volatile and there will be fluctuations above and below the mean. Different factors affect the weather on different time scales. For snowfall there are even more variables than for temperature. That is why we deal with averages and percentages, not absolutes. But the ENSO phase is probably the most powerful seasonal forecast tool yet discovered for a vast part of the globe. Another cycle I’ll briefly mention is the Pacific Decadal Oscillation which, due to its current cool phase (cool for Alaska), bolsters the confidence of this colder-than-average winter forecast. I covered the PDO more in last year’s winter forecast.

Please let me know what you think via the comments link below. And remember, don’t kill the messenger just because you don’t like the message.

Links:

NOAA NCEP ENSO page http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml

NOAA ESRL ENSO page http://www.esrl.noaa.gov/psd/enso/

NOAA PMEL ENSO data links http://www.pmel.noaa.gov/tao/elnino/measurements.html

Haines Highway, near the summit, with drifting snow, low visibility. Difficult, but drivable. The poles on either side of the road really help.

Since the winter weather has the potential to put a complete halt to highway travel, having an accurate forecast well in advance of a trip could save much time, money, missed opportunities, or worse. I consider this one of the most important uses of weather forecasting. Is the state of the art up to the task?

The state of the art

The raw truth is that there is precious little information available to meteorologists and the travelling public about the current weather (what’s going on right now) along Alaska’s highways. When you don’t have a good idea of the current conditions, its that much harder to make a forecast. The main problem is the enormous distances between traditional weather reporting stations. What about web cams? Yes, they do help fill some of the gaps, but they are restricted to areas with electrical power and telecommunications, so we are still left with vast stretches of mystery highway. Weather radar does not reach most of the areas of interest due to distance, and blocking of the radar beam by mountains (remember, the mountainous areas are the most critical for driving and also for affecting the weather). Satellite data is of limited help since it is not so good for inferring things like how much snow is piling up and whether there is reduced visibility due to falling or blowing snow. Much of the diagnostic work is done just as the prognostic work: by looking at the various charts and inferring the conditions on the ground, using local knowledge as a guide. All these challenges mean that weather info for the more remote sections of highways is not good enough to make a go/no go decision on a trip more than a few hours in advance. The good news is that if your are properly equipped with a good vehicle/tires, winter driving skills and provisioned for any contingency, you can most always make it through despite the weather, though the time needed may vary.

The targeted highway forecast

A few years back the NWS put out “motoring” forecasts for all the main year-round highways in the state. With two exceptions these have been absorbed into the “zone” forecasts. The thought was that the zone forecasts now cover the entire state, so the highways are covered in the various zones they fall in. So there is no need for a separate forecast. Well, I believe the change resulted in a decrease in service to the highway traveler. The reason is related to the reasons why it is so hard to forecast or even determine the weather along the highways. The lack of data encourages a forecast more tuned into the population centers and weather reports in the zone. The mountainous areas in a zone often have different weather and usually few, if any, weather stations. But the highways go through the mountains, nonetheless (yes, through passes, the low spots, so things aren’t as bad as they could be). The zone forecast can only stretch so far, and the highways (passes in particular) don’t get the treatment they used to. There are a few passes explicitly mentioned as locations included in the zone forecast, and that may help some, but there are only a few. Another issue is convenience: The route from Anchorage to Fairbanks passes through six zones. Other routes aren’t going to make you look up and piece together quite that many forecasts, but at least two or three.

The exceptional highways

There are two routes which avoided the axe: The Klondike Highway from Skagway to Carcross and the Haines Highway from Haines to Haines Junction. Maybe the need was seen for these two since they are two of the most weather-affected drives around, or maybe it had something to do with the international nature of the routes: both cross the coastal mountains while traveling between US and Canada. Perhaps the Canadian forecasters, who write the sections on their soil, wanted to keep it going. Either way, it is good that it is still done. In keeping with the difficulty of the task, the forecast is only valid for the current and next day (the evening version only for that night and next day, i.e.., 24 hours), and it doesn’t try to cover whether the road will be slick, icy, wet, dry etc. The forecast is released from October through April, which covers most of the possible poor driving conditions. Most, but not all. In June 2008 a large section of the Haines Highway was blasted with as much as a foot of snow!

These two remaining highway forecasts can be found at http://pajk.arh.noaa.gov/TextFcsts/textProds.php#prods=public.

Zone forecasts can be found at http://pafc.arh.noaa.gov/pubfcst.php.

Reading between the lines

As sketchy as they may be, checking the current conditions before heading out is crucial. Here’s a portion of the road reports for the two Southeast Alaska access routes mentioned above. This product comes out only once a day, in the morning. Notice that info from Frasier is missing. The report from the summit is valuable…those conditions are marginal but drivable. Another important bit here is the temperatures at customs (38F or +3C) and the summit (30F or –1C). The drop from above freezing to below freezing is most likely going to be the slickest part of the drive, and in this case it comes in the steepest section of the highway. Better have really good tires.

900 AM Saturday October 29, 2011

South Klondike Highway Weather Observations Between 7-9 AM Saturday

Mile	Location	SkyWx	Temp	Vsby	Wind	24Hr Pcpn	24Hr Snow	24Hr Max	24Hr Min
0.0	Skagway Airport	Light Rain	45	10+	SW14G21	0.02	M	47	42
6.8	US Customs	Rain and Fog	38	7	S10	M	0.0	M	M
15	Summit/Border	Snow and Fog	30	3/4	S15	M	3.0	M	M
22.5	Fraser	M	M	M	M	M	M	M	M
66	Carcross	Cloudy	31	10+	NNE4	T	1.2	31	26

For the Haines Highway it might at first appear there is more complete reporting, but look at the mileage figures. The first 40 miles from Haines are along the river flats…very little elevation gain. After passing the border the road climbs aggressively and crosses several high points, followed by many ups and downs. [more details including a satellite photo and nifty elevation profile can be found at the website of the bike race that takes place on this route each June, the Kluane Chilkat International Bike Relay.] By the time you get to Blanchard, the next point with any weather information, most of the weather issues are behind you (assuming you are northbound). At least on the Klondike Highway there is some information about the actual pass, here, nothing. That the visibility is zero at the border and only 4 miles at Blanchard could indicate a slow drive.

Haines Highway Weather Observations Between 7-9 AM Saturday

Mile	Location	SkyWx	Temp	Vsby	Wind	24Hr Pcpn	24Hr Snow	24Hr Max	24Hr Min
0.0	Haines	Light Rain	40	5	CALM	0.09	0	43	37
3.5	Haines Airport	Light Rain	44	10+	ENE13G22	0.02	M	45	39
23.8	Chilkat Rvr Bridge	M	35	M	CALM	0.03	M	42	32
36.6	Klehini	M	32	M	CALM	0.15	M	40	31
40.4	US Customs/Border	Cloudy	32	0	M	0.00	0.0	41	30
88	Blanchard	Cloudy	28	4	CALM	T	0.8	34	21
151	Haines Junction	M	M	M	M	M	M	M	M

The reports from 23.8 and 36.6 are from DOT automated wx stations with web cams. You can get them through the DOT website at http://www.dot.state.ak.us/iways/roadweather/forms/AreaSelectForm.html, or the state 511 website (so names because you can dial 511 on your phone to access the information) at http://511.alaska.gov/. The latter I find slow and cumbersome but at times contains valuable road condition reports that the DOT does not, since the latter does not try to give road conditions, just weather. More web cams can be found at http://akweathercams.faa.gov/. Although indented for flying weather these cams can help with highway weather as well.

More info

Don’t forget to check the basic weather stations. They can be found many places on the web. Two good ones for this are http://pafc.arh.noaa.gov/obs.php and http://climate.gi.alaska.edu/Wx/current.html. The latter is map based,which should lend itself to highway planning (but the highways are not shone). Be careful with this one…for some reason the times of the observations are in east coast time, and, I’ve found several stations that are not mapped in the right place. It would be great to have a really good map-based web page that showed all possible observations, cams and reported road conditions (and forecasts for that matter). Another thing I’d like to see is a way for drivers to report conditions they encounter and have those reports available to other drivers. We get reports from airplane pilots and ships and boats, why not cars and trucks? What do you think? I’d love to hear your opinions, comments and questions via the comments link below.

Winter forecast

Yes, I’m working on a post covering what might happen weatherwise during the coming winter. It might not be out by Halloween (it could be scary enough), but soon after.

Wherever you are, except maybe Death Valley, you might want to have a rain gauge to keep on top of the details at your location. What other piece of technology is so inexpensive, easy to use, durable and accurate? Here’s my 4 inch plastic model. (click for bigger picture). It consistently reads very close to the official NWS coop 8 inch rain gauge located less than mile away.

The overflow feature is handy here is Southeast. It works just like its big brother, the 8 inch metal gauge, which is the standard at the NWS and around the world. When the gauge begins to collect rain, it is funneled into the inner tube where the amount of rainfall can be read easily read in 1/100’s of an inch on the scale (A). When 1.00 inches have accumulated, the inner tube is full. Don’t worry, there is a channel (B) which directs the overflow into the outer tube which can hold much more. When it’s time to take a measurement, the inner tube is emptied and the overflow poured into, and measured with, the inner tube (filling and emptying as many times as needed) to get the total. In this photo you can see that the rainfall came quite a ways up the overflow tube (C) while our family was away for three weeks. The total was 5.20 inches (132 mm) (and that was in August, not our real rainy season). If one had left for the same dates from Ketchikan, even the overflow tube would not have been able to handle the 16.05 inches (408 mm) that fell there!

To rate the summer weather we first need to define “summer.” Back on the summer solstice I talked about how that date is only an astronomical event, not one that really marks the start of summer, since most of the best Alaskan summer days are history by June 21 and many of them by June 1st (see the article). And when does summer end in Alaska? There are many markers that could be reasonably argued for the end of summer, and certainly it does not have to end at the same time across this vast land. The fall equinox (which happens to be today) does work pretty well for most of the state, but for the sake of symmetry I’m using May 15-Sep 15.

Here’s a series of graphs for 6 cities across Alaska. You can get the basic picture on this screen…or for more detail click on a graph for a full sized version. I’ll touch on how to read the graphs during the first set of observations, for Barrow:

The red trace is the high temperature of each day of the summer. The jagged spikes and valleys are variations in the high temperature from day to day, not from a daily high to a nighttime low as in graphs in other articles. (For why I’m using high temperature, and not average of high and low, see the this post.) The smooth black curve is the daily “normal” or climatological average, computed over the past 30 years (these are the brand new NCDC 1981-2010 normals, by the way). Barrow is the coldest city in the USA but keep in mind the contest rules say that it’s a city’s summer weather with respect to their average that counts, otherwise Barrow would be a shoe-in. This summer, the Top of the World’s highs were overall 1.6°F above average, the relatively warmest of the bunch.

For precipitation, I’ve borrowed graphs from UAF’s Alaska Climate Research Center. (Yes, I did the temperature graphs…using the free spreadsheet Gnumeric and the free vector graphics software Inkscape.) The precip graphs don’t cover the same time period, so check the dates along the bottom. Also note that the scale of accumulated precipitation along the left side is scaled according to the station’s average annual amount, so Barrow’s goes up to 6 inches while Juneau’s goes to 70. But again we’re comparing this year with the average, so its fine this way. What you want to focus on is the slope of the green line compared to the black. That will tell you the rate of accumulation, i.e., how much rain came at certain times compared to the climate. Barrow started the summer with a large surplus built up the previous November and February. During the summer, next to nothing came down until mid-June, but then not at anything much more than average. I’d say Barrow’s summer was a little better than usual given the temperature trace. Moving south to the next contestant, Nome.

Nome’s a tough competitor when it comes to lousy weather. I should know, I cut my meteorological teeth there as an intern with the NWS. But the Gold Rush City was slow out of the gate this summer. Temperatures started a bit above average on May 15th and warmed nicely, spiking to a new record high of 71°F on the  27th, then to 75°F on the 28th (only tying the record). The 28th was Saturday, so it was an amazing start to the 3-day Memorial Day weekend. But it was all part of a brutal psychological strategy: the high on Sunday the 29th only made it to 47°F, and on Memorial Day only to 41°F!. The judges will surely reward this bait and switch. After that, only a single day made it to 70°F and highs were mostly below normal. In another holiday smack down, Independence Day started with a light frost and only managed 45°F for a high. Labor Day had mild temperatures, but winds gusting to 43 mph. Surprisingly, highs were only 0.2°F below average for the summer period.

On the precipitation side, Nome was about average in May and June, then took off in July and August. The July total was twice the normal amount and August 135%. Strong storms hit the town with regularity during this period.

With a summer deviation of 1.4 degrees F above normal Fairbanks’ temperatures are not going to win this contest. Besides the Memorial Day heat shared by many areas, there was a high of 88°F on 25 June coinciding with around 4,300 lightning strikes in the interior, which started 10 new wildfires. Otherwise, there were not a lot of extreme temperatures for the Golden Heart City. A string of nice, warm days in late August and early September made up for some of the cloudy cool weather earlier, further eroding Fairbanks’ chances at the lousy summer prize.

Similar to much of the state, Fairbanks and the interior were quite dry for the the first part of the summer, then went into catch-up mode in June. Look at the long flat section on the precipitation graph: very little moisture from late February till into June, then a steep climb. The high river levels that resulted washed out both the Taylor and Steese highways in June and flooded the Salcha River in July. The active wildfire season during the dry season was cut short when the rain came and in the end the acreage burned was only 1/3 of average. Events like that boost the interior’s position in the worst summer race, but will it overcome the poor temperature performance?

Alaska’s big city had a pretty unremarkable summer. If residents think they had a bad one, I’ve got news…you live on the ocean and cloudy and cool are to be expected. Some of the warmer summers of recent years have spoiled you. OK, it was a little cooler than normal with summer, as we defined it, 0.8 F below average, and only 7 days reached 70 F. (This is at the airport—it’s a usually a few degrees warmer on the east side of the city).

Precipitation was a little low for the early summer but not as dry as the interior or as parts of Southeast even. In fact even in June there were 20 out of 30 days with at least a trace of rain, but amounts were small. July was better in that there were 16 dry days but August had only 4 dry days. Not a great summer, but not exactly medal material either. Lets move southwest.

Cold Bay is very maritime, so we don’t expect much in the way of temperature swings, and that was the case, as you can see on the graph. If the ocean water is cooler than usual, the temperature will follow suit. Over the summer the average max temperature for Cold Bay was right about 1°F colder than average. If it wasn’t for a few warm days scattered here and there, especially the two spikes in mid August, the average would have been quite a bit colder. Being so maritime in climate, Cold Bay is also slower to warm on average, so the traces of snow on May 8 and 15 were not that unusual.

No, I did not mistakenly put in the wrong graph here. There was none for Cold Bay, and King Salmon was the closest available. That’s what happens when you borrow your graphs. (The total in the chart at the end of the post is for Cold Bay). Cold Bay and King Salmon bucked the pattern of most of the rest of the state and did not have a very dry first half to the summer. In fact both were relatively wetter in the earlier months. In short, a wet and cool summer for the region. But is it enough to win?

Juneau’s average summer highs are surprisingly close to Anchorage’s (comparing airport to airport), but this year instead of 0.8°F colder than average like Anchorage, the Capital City was 1.8°F colder. Juneau did have 10 days of 70°F or warmer compared to Anchorage’s 7, a volatility evident looking at the respective graphs. From mid July through the first few days of September highs were well below average every day but a precious few that barely broke the black line. The raw numbers definitely favor Juneau as the cold summer leader.

Juneau, and Southeast Alaska in general, followed the trend of most of Alaska with a dry first half of the summer. In fact the pattern was more pronounced here than most areas, and north of Juneau, in Haines and Skagway, it was yet more dramatic. See the details here. Meanwhile, in the southern panhandle, Ketchikan was running at around 200% of average for July and August, including an impressive 3.69 inch dowsing on July 1, right in the heart of the “dry season.” A couple record events in August brought even more rain to the southern half of the panhandle the wettest one day total being 5.42 inches at precipitation powerhouse Port Alexander on August 20, smashing the 1958 record of 3.15.

The envelope please

Here’s a summary table for the six cities reviewed. Remember it is the deviation from average that makes or breaks the case for worst summer weather. Who do you think deserves to win?

I think Juneau should get the worst summer award, to be shared with all points south in the panhandle. Nome comes in a strong second and Cold Bay and the southwest coast deserve an honorable mention. They rest of you are just being wimps or complainers.

Admittedly I’ve only looked closely at six stations, so some deserving folks might have gone unnoticed. Therefore I’d love to hear your take on the contest (with evidence), and any input or ideas via the comments link below, as well as donations of blankets and umbrellas for prizes.

And yes, I’m gearing up for a shot at the winter 2011-12 forecast. Stay tuned.

At the surface of the earth the pressure is around 1000 mb (or one bar, or atmosphere), so the 500 mb level is about 1/2 way up the atmosphere in terms of pressure or mass. in other words, half the air is below 500 mb and half is above. The actual height is another story. Air pressure does not decrease steadily as you go up in the atmosphere, it decreases logarithmically…the decrease in pressure happen quickly at first then gradually slows. The 500 mb level is  roughly 5,500 meters up (18,000 ft). The contour lines are labeled as to their individual heights.

What does this map tell us?

In general a 500 mb chart, or any upper level chart, shows the pressure pattern, and the wind flow for the valid time, whether that be the time of the actual measurements for a diagnostic chart, or the time of the forecast for a prognostic chart (prog for short). More interesting is what this upper level flow means for the weather down here on terra firma. But first a little more info way up high. The map above does not explicitly show the winds, but they can be deduced from the contours. Upper level winds flow pretty much parallel to the contours, counter-clockwise (northern hemisphere) around lows–an area of low heights on upper level charts being the same thing as an area of low pressure, for all practical purposes. The wind speed is proportional to how close together the contour lines are. In this map there are two lows, one big one in the upper left in the far western Bering Sea, and a smaller one half off the bottom of the frame. If you connected these two with a line, you’d be describing the axis of a larger, more general feature, a trough. To the east, or downstream in the wind flow, the contours bend up (north) then curve back south to describe a ridge. The strongest winds are around the west and south sides of the larger low, over the Kamchatka Peninsula and south of the Aleutian Islands, whereas the Alaska Peninsula is in a slower wind area, for instance.

What does it tell us about our weather?

Unless you are up in an airplane, where you will rely on upper air charts directly, what these maps mean for surface weather is of primary interest. The 500 mb chart is good for showing where surface lows and highs will develop and where and how fast they will move. Pretty useful, I’d say. Here’s the super condensed version of how this works: The area from a trough axis downstream to the following ridge is an area favoring development of low pressure centers and fronts at the surface. The area under and downstream from a ridge is an area favoring high pressure at the surface. Remember, entire books are devoted to this interconnection of the upper and lower layers of swirling air, the dynamics of the atmosphere, so what I’ve just let on could be the mother of all simplifications. Many 500 mb charts, this one included, show an additional parameter in an effort to reveal the dynamical processes at work. It the the vorticity field, and for now lets just say the higher vorticity values (shown in the color scheme as tending toward red), are where the dynamics are more favorable for low pressure development at the surface. This is also a big oversimplification, but I wanted to mention it since it is on the chart. Take a look at the 500 mb chart above and see if you can envision the areas where surface lows and highs might want to be, then look at the computer’s vision on the surface prog for the same time, from the same model:

The serious action at the surface is in the eastern Bering sea under and a little downstream (east) of the 500 mb tough and low. The smaller low at 500 mb (the one near the bottom of the map) also has a surface low counterpart a little downstream. But now look at the 500 mb ridge which has its axis a ways offshore of Southeast Alaska and continuing northwest through roughly Prince William Sound and the northwest arctic coast. On the surface there is high pressure a ways downstream from it, centered over Yakutat at the neck of the panhandle. There’s dynamics at work.

What does it all have to do with the Northern Lights?

Actually, the atmospheric patterns aloft or at the surface have nothing to do with the aurora (or northern lights). But they have everything to do with whether you will be able to see the potentially strong aurora likely to be happening over the next couple of days at the very upper edge of the atmosphere, roughly 30 times higher than the 500 mb level. The 500 mb ridge is nicely situated to give Southeast Alaska the best look at any auroral activity. The southcentral region may get some breaks, but it is not as well situated as the panhandle, were the offshore flow should make for talk-of-the-town good weather. The eastern interior, which has had its share of nice weather recently and is drier by nature won’t even do as well as the panhandle, as the high will probably not be strong enough to clear things up completely. For the panhandle, Sunday should be the best day, for the other areas, not so much difference between Saturday and Sunday. The western half of the state. on the other hand, things will be gong downhill fast as the dynamics of an upper trough come into play. Lots of moisture and even more wind are headed for the west coast and the Aleutian chain. The NWS has high surf advisories out already for many west coast areas.

You can check for yourself, not only the 500 mb chart, but all the levels, plus the latest info on solar activity that might spark a good aurora. Here are some links:

Upper air:
http://pafc.arh.noaa.gov/gfemodel/index.php
http://weather.uwyo.edu/upperair/uamap.html

Aurora:
http://www.swpc.noaa.gov/forecast.html
http://www.spaceweather.com/
http://www.gi.alaska.edu/AuroraForecast

Please let me know if you see the aurora, a coastal storm, or something in between. Use the comments link below for your report or any questions or comments you might have.

PUBLIC INFORMATION STATEMENT…CORRECTED
NATIONAL WEATHER SERVICE FAIRBANKS AK
316 AM AKDT TUE AUG 30 2011

CORRECTED THE HIGH TEMPERATURE AT FAIRBANKS

…THE UNSEASONABLY WARM WEATHER CONTINUES IN THE INTERIOR…

A RIDGE OF HIGH PRESSURE ALOFT HAS BEEN RESPONSIBLE FOR THE
WARM WEATHER DURING THE LAST SEVERAL DAYS ACROSS MUCH OF THE
INTERIOR. MONDAY WAS THE WARMEST DAY OF THE BUNCH IN MANY AREAS.
HERE ARE SOME HIGH TEMPERATURES THAT WERE OBSERVED MONDAY AFTERNOON:

DENALI NP HEADQUARTERS….74
FAIRBANKS INTERNATIONAL…72
NORTHWAY………………71
FORT WAINWRIGHT………..70
NENANA………………..70
TANANA………………..69
EIELSON AFB……………69
EAGLE…………………69
DELTA JUNCTION…………68
FORT YUKON…………….68

Only the southern end of the SE Panhandle could get near the interior’s highs today. Nothing record breaking, but very nice nonetheless. What is not mentioned in the statement is the low temperatures, which are getting downright chilly. This is no surprise, as the same weather pattern which allows the solar heating to warm the afternoons also allows the radiational cooling to cool the nights and early mornings. I covered this topic more thoroughly in this post. So it is also no surprise that the state’s high for today and low for last night are only a stone’s throw apart (Alaskan speaking) at Northway (68 F/20 C) and Eagle (31 F/-1 C). Eagle was 70 F/21 C yesterday.

Now take a look at the Fairbanks Airport temperature trace for August (shy a few hours):
(click for larger version)

The small magenta spikes near the bottom of the chart show precipitation (rain) which is a good indicator of the kind of heavy cloud cover which moderates the temperatures, keeping the diurnal range low. Most of the middle of the month was in this mode, with a few days of relief interspersed. The first five days and the last week were dry and more clear, allowing the large swings in temperature. This is nothing new to many, and as I mentioned, nothing new to this blog (here’s the other article).

What you might not have thought about, however, is how the daily average temperature records can mask the differences between these two regimes. I’m talking about the human experience…how nice it is or was for outdoor activities. To get this story from the weather records, the  daily average temperature downplays what you and I experience as the day’s weather. The recent interior warmth is a good example. During the past week it was so nice that the NWS folks made official acknowledgement. Sunny, warm, pleasant weather with the highs about 6-9 degrees F warmer than the climatological average. However, since the lows dropped lower with the clear weather (they were fairly close to the climatological average or “normal” in NWS lingo), the daily average [(high+low)/2)] was only 3-6 degrees warmer than usual. So when considering how the weather affects daily life, looking at high temperatures makes more sense to me than the day’s average temperature so commonly given in climatological reports. However, in the midst of the winter, I think low temperatures are the more important factor for the human experience. I’ll save that explanation for another post. What do you think…of which measure to use and whether those Fairbankskans deserve this good weather?

Here’s the precipitation data for the past three months in map form, then more completely in table form–arranged top-bottom in case you need some help in identifying what towns the numbers on the map belong to. Look at the large variation in a bit over a hundred mile radius, with the dry bulls eye over Skagway:

The “years” column is the number of years of data that went into the average and extremes.

What’s behind the dry spell/dry spot?

Check out this recent surface map, a very recurring pattern this summer. The large high over the North Pacific is a semi-permanent summer feature and is in fact officially called the North Pacific High. Strong highs like this are effective at keeping frontal systems from impacting Southeast with any strength or regularity. That front slicing down through the interior and Cook Inlet brought about a quarter of an inch of rain to Anchorage and other areas, but fell apart (as most have) while trying to rake across the top of the high, and the panhandle got almost no rain.

However, for coastal stations, highs do not mean all is dry and sunny, for they push the ample oceanic low clouds (commonly called the marine layer) onshore, bringing not only clouds, but a mix of fog and drizzle and a smattering of light rain as the moisture gets wrung out of the marine air by our abrupt coastal mountains. But rainfall will stay below average with this kind of pattern. Bet why are the northern inner channels so much drier? They are protected from the both the low marine layer and the orographic (mountain induced) precipitation by the first several ridges of the coastal mountains. In a sense Skagway and Haines are not very coastal, but a little more like the interior. Everything is in shades in the weather business.

What’s next?

Will the dry weather continue? Climatology indicates that things must start getting wetter fairly soon. Even in super-dry 2009 the rains came in August and September, playing a strong catch-up game in the area. Such is the flip-floppy nature of the weather in much of Alaska.

The computer models are not showing a major shift for the next week anyway. There is some weakening of the pattern and there will probably be a little more moisture than we’ve seen, but probably very little in the protected areas discussed above. Our gardens could use a lot more than I think we’re likely to get over the next week. The real weather is the continuing strong lows moving into the Bering Sea, an example of which is pictured in the surface chart above. The west coast is getting way more storms than they probably want. The longer range maps from the Climate Prediction Center are not wanting to deviate from climatology (in other words they’re not sticking their neck out for above or below normal precipitation), except for continued wetter than normal for the next two weeks for the southwest part of the state.

The big issue for Haines is the upcoming Southeast Alaska State Fair coming up in two weeks. Despite Murphy’s laws on rain, its too early to say whether the fair will be warm and sunny, cool and rainy or somewhere in between.

I’d love to hear any comments or questions on this article, or any weather topic. Click on “comments” below, and let me know whether your hoping for rain or sun where you live.

This histogram shows the percentage of time each station received the listed amount of precipitation on July 4th over their period of weather records, 68 years minimum. Of these 4 metro (“Alaskan metro”) centers it is surprisingly Anchorage that comes out driest. Another surprise is that Juneau and Fairbanks are right about the same! I’d guess that Fairbanks’ rain is more showery and therefore more brief, allowing more sunshine than Juneau’s marine cloud layers. Barrow has more dry days than Fairbanks as well, but fewer days with more than a tenth of an inch…the kind of rain that can really soak a picnic.

What about this year?

The following computer forecast is for 10 am on the 4th and shows wind barbs at the 700 mb level (~3,000 m/~10,000 ft) and relative humidity through all levels.

There are three lows threatening to rain on our parades. One near Kaktovik in the northeast corner of the state, one over the Seward Peninsula between Kotzebue and Nome, and one offshore of Southeast Alaska. Each is feeding moisture via some strong onshore winds. The Seward Peninsula low will hit a little later, hopefully after the celebrations.  If its not raining it will certainly be cloudy in for the Panhandle, especially the southern parts. Similar for the north slope although leaning more towards low clouds, drizzle and fog. It does not look quite so bad for the the interior and Southcentral…clouds and perhaps some light rain or showers. Click here for a more detailed, up to date NWS forecast. Then let me know how your 4th was, weatherwise and otherwise.