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It’s been a cold winter across most of Alaska. It’s not the first and it won’t be the last. During every winter there are relatively colder and warmer periods. This year these cold snaps and warm spells seem to be aligned pretty well to the calendar months: November was cold, December warm, and January…one of the coldest, especially for the rail belt and everywhere west. Check out the write-ups from Weather Service personnel in Anchorage http://pafc.arh.noaa.gov/papers/THE%20COLD%20FACTS.pdf and Fairbanks https://nwschat.weather.gov/p.php?pid=201202012052-PAFG-NOAK49-PNSAFG. February is staring off with a big warm-up, thanks to a strong low barreling into Alaska’s midsection like a gut punch. I’m not making any promise that this trend will hold for February. It does look like a week to 10 days’ break for from the cold, but beyond that, I’d be surprised if we don’t get a fair amount of more cold weather (and snow for the coastal and near coastal areas) before the winter is over. See the Climate Prediction Center for more. For this post, however, I want to zero in on an interesting pattern that seems evident during the worst of the cold snaps. Let’s start with this map, used by permission of the Anchorage Daily News.

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.

Alaska is a big place, and the weather system affecting our state right now is even bigger, but I’m going to show you that is it the small scale that counts when it comes to winds of the south and southeast coasts. As I write this, virtually the whole state is under the influence of the strong pressure gradient between a large, deep low in the Northeast Pacific and strong but gradually weakening high pressure in Siberia and the Alaska interior. (The high was up to a crushing 1060 mb a few days ago, compared to the still hefty 1040 mb on this map) Here is the surface map from 3 pm/00z this afternoon from the GFS model (It’s the 12 hr forecast which is about as good as an analysis):

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.

Polar lows are small, somewhat elusive, and usually quite potent…cool stuff for weather watchers. They are small compared to their more common, mid-latitude big brother lows, up to a few hundred miles across, compared to a thousand or more miles across for the later. They are more like the size of hurricanes. For that reason, and because they sometimes look a lot like hurricanes on satellite imagery, and because they do share some structural similarities, they are sometimes called arctic hurricanes. The Bering Sea is a hot spot (sorry for all the puns) for polar lows but certainly not the only area…the North Atlantic is a good place too. A interesting polar low recently tracked across the southern Bering, strongly affecting the Pribilof Islands: St. Paul and St. George, but each of the two in curiously differing ways, as we’ll see. Here’s the Infrared satellite image from 15 UTC  (6 am AST) on Jan 3rd. The polar low was still about 200 miles west of the Pribilofs. With most typical low pressure systems, they’d be in the thick of it, but this average-sized polar lows is not yet affecting their weather:

Polar lows often are most impressive on satellite images (many show a more “closed” look than this one) and less so on surface maps due to their size compared to the scale of the typical maps. (more…)

My tips for witnessing unusual, interesting or simply beautiful weather phenomena have always included spending as much time as possible outdoors and keeping your eyes up, as in looking up at the sky often. A couple days ago I found some unusual weather down at my feet. Snow rollers! My other advice is to always have your camera with you, which I did not, but it was close and I was able to fetch it before the mid afternoon dusk turned to complete darkness. Between the duskiness, the falling snow and the flat light, my photos turned out pretty rough, but by the next morning, after a few hours of rain, the snow rollers were history…you would not have suspected a thing. (Please click on the photos to see larger versions.)

Snow rollers form when the snow possesses a certain layered tackiness that allows the top layer to peel off the underlying layer (or sometimes the ground) and stay together as it gets rolled into a ball or tube. The rolling can be bone by either gravity or the wind. No elves or gremlins are needed. If by gravity, a pretty steep slope is usually needed. If wind, then you can guess that a pretty strong wind is needed. (more…)

Not all of Alaska is in the rainiest time of the year right now, but the southeast arm of the state, also variously known as the panhandle, the Inside Passage, the Banana Belt, or just plain Southeast sure is. In fact, I like the term rain coast. Farther north the rainiest time tends to be earlier in the year. With a few exceptions, the wettest month in Southeast is October, in Southcentral and the Interior it is September or August and along the north coast and most of the Bering Strait and Bering Sea coasts it is consistently August. The southwest coast and Aleutian Islands don’t show as clearly defined wettest month but there is no doubt that September through December or January is the wet time. These graphs illustrate. The green line is the precipitation, the others temperature. Note that the scales are the not the same on all graphs. The precipitation scale (on the right) is the same for all but Ketchikan, where it had to be expanded upward to handle the larger amounts. The temperature scales are less consistent.  (that’s what you get when you borrow your graphs…these borrowed from the Western Regional Climate Center.)

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Most Alaskans had reason to complain about the recently departed summer. Not that having a reason has kept anyone from complaining in the past. I invite you to check out the hard data below, compare it with your experience and let’s see if we can come up with an award (sorry no prize money) for the worst 2011 summer in Alaska. I’d like to hear your experience and opinion on this high level competition.

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:

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Everybody has an impression of how the winter turned out, but what do the numbers say? Was the long-range prediction for the winter I made in November at all accurate?

Well, the impression expressed by most folks here in Haines, in the northern panhandle, is that is was a very cold winter. Looking at the two maps below you can see that, yes, the northern panhandle was quite a bit colder than usual this past winter—one of our coldest winters on record, actually. Furthermore the northern and eastern panhandle was the relatively coldest part of Alaska this winter…relative to each station’s long-term average.

The top map shows departures from the long-term average (or “normal”) for November through March, what I and many like to consider the winter months (for interior and arctic areas I might say “core winter months”). Haines was in the winter bull’s eye, with a winter 3.5F (1.9C) colder than average, with Juneau and Petersburg almost as cold. (I’ve not checked all the stations in the area, so I’m only referring to the sample plotted.) The cold anomaly drops away for the far south and outer coast of the panhandle. Yakutat was above average and you can see a similar positive departure of 0.6 to 1.8F (0.3-1.0C) along the rest of the gulf coast and right up into the Bering Sea to Nome. The northwest coast was dramatically opposite the southeast coast in that it was way warmer than usual. Inland areas of Southcentral and the Interior were average to about 2F (1C) below average.

The next map shows the same thing as above but for December, January and February only. This is so a direct comparison with the D-J-F seasonal forecast can be made. The pattern follows the Nov-March map above but the below normal areas are even colder, especially the interior, while the warm pocket in the NW is also a little cooler. How does is compare with the 3-month outlook put out in November by the Climate Prediction Center? (click here for that post) The CPC map had virtually all of Alaska south of the Brooks range being below normal. I’d call it a good forecast for that area. The missed forecast was of the way-above-normal area on the Northwest slope, with Barrow being the bull’s eye of warmth. A closer look at Barrow’s anomalies is in order for another blog post.

How about precipitation? The CPC predicted neither wet nor dry but “equal chances” of it going either way or staying in the middle. I predicted snowier than usual in SE Alaska and possibly snowier in Southcentral. The map below shows that my snow forecast was a bust. Snowfall was light by a fair amount in most of the panhandle (A little heavy in Petersburg), and a little on the light side in Southcentral. The miss in this forecast was the heavier then usual snowfall in the NW third of the state, with over twice the average in Kotzebue and Barrow. For this blog post I’ve tabulated snow and not precipitation (rain plus water content of the snow). It would be good to check actual precipitation, but it is likely that higher snow meant higher precipitation for the the interior and arctic since virtually all the precipitation is snow in winter in those areas. Coast and southern areas on the other hand often have above average precipitation simultaneously with below average snowfall, since in warmer weather rain falls even in winter. Most of the time is was cold and dry, especially for the northern panhandle, so I think you would find that precipitation was low too. My higher snow forecast in these areas was based on cooler temperatures shifting rain to snow. What appears to have happened is that so much of the winter was spent under the influence of the cold offshore (dry) winds that the precipitation was not frequent enough to boost snow amounts (or rain amounts). Meanwhile in the NW third of the state, winters are so cold that increased warmth almost always means increased moisture.

Now the Why

Here’s a look at the wind and pressure patterns that are responsible for the lopsided maps above. First is the 500 mb height anomalies for November-March courtesy of NOAA’s Earth Systems Research Laboratory, Physical Sciences Division. Click on the map to see a larger version. What it is telling us is that at the mid-atmosphere level, averaged over the winter, there was a strong ridge (higher pressure) aligned generally N-S over the Bering Sea, while there was slightly lower than normal pressure (a trough or low) to the southeast as seen in the blue. The flow over this average ridge brings much very cold air to Alaska from Siberia and the high arctic, while also protecting most of the state from low pressure systems. There certainly were Bering Sea storms (remember this is a 5-month average), but the average storm track was shifted west, affecting the west coast the most (referring back to the first two maps reminds us that the west coast was warmer than average). For a good example of a strong storm kept well to the west by this pattern see A Far West Alaska Blizzard from February.

Here is the corresponding sea level pressure anomaly map. The red area is higher than average surface pressure.

Winter highlights

November 22-24 freezing rain in the Interior: A rare heavy mid-winter rain fell on subfreezing ground causing severely iced roads and runways, broken tree limbs and downed power lines. Rain fell for 39 hours in Fairbanks for a total of 0.95 inches (24mm) while McGrath had 2.10 inches (53 mm).

December cold snap: Most areas of Alaska except the far west and northwest were 5-10F (3-6C) colder than average with Bettles being likely the coldest with a monthly average temperature of –21.4 F (-29.7C), an amazing 14F (7.8C) colder than the long-term average. There were many –40F to –50F (-40C to –45C) days in the interior. Even in relatively mild (for the interior) Glennallen, there were only two days in the month not below zero F (-18C).

February Super High: The sea level pressure was so high that many aircraft could not set their altimeters to the current setting, because most can not be set to over 31.00 inches Hg (1050mb). The high pressure was not confined to the interior, but was also over 1050 mb over the Bering Sea…a rare occurrence….but it also happened in November. See Pressure Extremes and the Migrating High Winds for more.

April super-storm: The storm that hit Alaska on April 6-8 was a ex-tropical storm, and these are known to pack a punch of wind and especially precipitation. This one went out of its way to keep up the reputation. Most of Southwest AK had blizzard or near blizzard conditions and many had damaging winds. In False pass two homes lost their roofs and several other buildings were damaged. Many stations had record wind gusts and/or snowfall. As the storm moves north and east high winds blew through mountain passes and gaps in Southcentral and coastal areas received heavy snow. Valdez received 31 inches (79 cm) of snow on the 7th and 8th.

Summer

Can a 3-month forecast for the summer have as much chance of usefulness as the winter forecast seems to? Generally summer is less predictable than winter, but also less volatile. I will post on this soon. Check back, and in the meantime I’d love to hear what your winter was like.

The marine forecast has been calling for heavy freezing spray quite a bit the last few weeks, and here is a graphic example of what they are talking about:

This is not the Bering Sea, this is Lynn Canal in the “protected” Inside Passage of southeast Alaska! The crabber Perseverance, home port Sitka, pictured above was out tending her pots this past Sunday (2/27) and came into the Haines harbor with this catch, despite the crew having beat the ice off more than once while underway. The winds were quite strong and gusty even inside the breakwater, with some nice little whitecaps. The gusts did not need much distance to produce these waves…they hit the water with such a downward component that they really “grip” the water. This is one reason our cold dense air packs such a punch (in addition to simply the higher density).

The wind out on the Canal was blowing around 40-45 kts (20-23 m/s) sustained with gusts to around 60-70 kts (30-36 m/s), based on measured speeds at Skagway and Eldred Rock. The air temperature was about 12 to 14 F (-10 to –11 C). The wind speed and air temperature are the primary determinates for freezing spray followed by size and steepness of the seas, water temperature and vessel factors such as speed and heading relative to the wind and seas, and hull and superstructure characteristics. You can see that it is not too hard to predict the potential for icing, but how a particular vessel fares in the conditions depends on too many variables.

Why so many days of strong offshore winds?

We ask this just about every winter, and not just in the panhandle but all along the Gulf of Alaska coast, from Sitka to Sitkinak, and inland a ways. The rapid loss of heat over the northern land masses in winter favors a cold, stationary, high pressure air mass over the continent while over the oceans (which retain their heat much better) low pressure systems of various strengths and speeds prowl the oceans, occasionally driving onshore. Sunday’s surface map is a great example:

The pressure difference, or gradient, between the two areas drives the offshore flow. But this high-to-low flow is only the raw material. Our winds would be very different without the sculpting by the mountains. The coastal mountains block, steer and accelerate this flow into the extremes of speed and direction we see so often in coastal Alaska. This is why at Valdez (at the NE corner of Prince William Sound) on the 28th the wind was from the northeast with gusts to 67 kts (35 m/s or 77 mph) but at Whittier (NW corner of the sound) it was gusting to 44 kts (23 m/s or 51 mph) from the southwest. Meanwhile at the Cordova airport (SE corner of the sound) winds were all around the compass and under 10 kts (but you can bet there was a strong north wind out of the Copper River just a few miles to the east)! Here are some peak gusts in Southeast Alaska nicely laid out on relief map by the folks at the Juneau NWS forecast office:

The 150 mph gust was at Sheep Mt., at 3,540 ft (1,160 m) elevation. The 104 was Cape Spencer and the 92 was Eldred Rock, both at sea level but exposed to the channeled outflow winds.

How long before we get a break?

Late winter is really the most likely time for an entrenched pattern, and the current pattern is starting to look pretty entrenched. Look at the upper level flow (500 mb) forecast for a week down the line…an omega block pattern. Too early to say how persistent this one will be.

That does not mean there will be no breaks, but we are likely to continue with predominately offshore winds through March, though less likely at the recent high velocities after mid-month. The land-sea temperature contrast talked about above will weaken along with winter itself. I’m basing this on climatology modified with the La Nina pattern for this region, which has played out pretty much as expected so far this winter. So why stray? Looking at the shorter term, the models are indicating a few days’ break from the winds plus a bit warmer and some light snow in places around Southeast and Southcentral AK. Then next week the cold offshore winds should pick up again for SE while SC may get a longer break.

If you feel like you need a break, take one while you use the comments form to post a comment, question or whatever weather or climate thoughts are on your mind.

I probably blog too much about Southeast Alaska (it’s where I live), so for this post I’m going as far away from SE as one can go and still be in Alaska. Lets look at what Shemya, near the far western end of the Aleutians, and Barrow, on the peak of Alaska’s roof (and points between) have been dealing with weatherwise.

A first class Bering Sea winter storm is just getting through pummeling the far west frontier. This low easily qualified as a meteorological bomb as it deepened rapidly from Japan, across the Aleutians, up the western edge of the Bering Sea and is now weakening northwest of Barrow. Click on the map below to open an animated GIF of the storm’s progress.

Here’s some of the weather brought by this storm, listed from south to north:

Shemya: “The rock” was hit early and hard and right on the tail of another storm. Late on Tuesday the 15th south winds picked up and were gusting to over 50 mph (80 km/hr) most of the night, all of Wednesday, and into Thursday morning. The storm had a peak gust of 75 mph (121 km/hr) in the wee hours of the 16th.  Intermittent precipitation oscillated between rain and snow.

The upper air sounding for Tuesday afternoon at Shemya. Note the strong winds at all levels with 135 kts (150 mph) jet stream winds at around 10 km (33,000 ft). Soundings were missing during the highest winds. Most likely the winds were just too strong for even the Shemya techs to successfully launch a 6 foot (2 m) diameter weather balloon.

The Pribilof Islands: The mid-Bering island group was far enough east to miss the strongest winds, but did have plenty of southerly weather with 30-45 mph (50-70 km/hr) gusts and rain and/or wet snow. This was followed by the cooler westerly flow around the back side of the low, dropping temperatures below freezing and bringing snow and a little drifting and blowing snow.

St. Lawrence Island: Savoonga had around 15 hours Thursday (2/17) with visibilities in snow and blowing snow less than a mile (1/4 mile or 400 meters much of the time) and winds sustained at 30-40 mph (50-65 km/hr) with gusts as high as 69 mph (111 km/hr). Gambell got off a little easier.

Nome: Conditions in the Gold Rush City were much less severe than most in the region. There was some snow and blowing snow and wind gusting to around 40 mph (65 km/hr), but the worst only lasted a few hours on Thursday. Currently however, a secondary low and front behind the first is giving them a 2nd act: Winds have switched back to southeast and increased and snow and blowing snow are back. (see the satellite image below)

Secondary front bullseyeing Nome.

Kotzebue: A slightly subdued version of the Savoonga experience, but with temperatures quite bit colder: from the low single digits (F) (-15 C) on Wednesday rising to the mid 20s F (~-4 C) Thursday compared to 20s and 30s F (~-5 to +5 C) for Savoonga. That kept wind chills down around 15-25 below zero F (-25 to -30 C) through early Thursday.

Point Hope: Fared about the same as Savoonga, but with not quite as high of gusts.

Point Lay: The airport web cam  for Friday mid-day tells the story (compare with stock clear day photo on the right). The low visibility is most certainly caused, as in the other towns, by snow and blowing snow, not fog. Even though many observations report fog during snow storms, it is most often not present — a topic for the future.

Barrow: By the time this storm got this far north it was weakening, but only slowly. The top of America had winds gusting to around 45 mph (70 km/hr) with visibility around 1/4 mile (400 m) in heavy snow and blowing snow as of the time of this writing Friday afternoon. The temperature, which had been well below zero F (<-18 C) a couple days ago had risen to +16 F (-9 C) around midnight Friday, but has been dropping again as the low tracks into the Arctic Ocean, dragging arctic air around its south side.

Here’s the last 24 hours of observation at Barrow (times are in ADT):

Site M/A Day Time Sky Conditions           VIS Weather Temp DP Wind(kt)  Alt  RH  Chill Peak

PABR  AA 17 2153  SCT090 BKN150              9          12   8 18018     929  84%  -7
PABR  AA 17 2253  BKN100                     5 BS-      13  11 18020     927  91%  -6
PABR  AA 17 2353  SCT095 OVC150              4 BS-      13  11 19018G26  925  91%  -5  27
PABR  AP 18 0000  CLR                    1 3/4 BS-      12  10 19018G26  925  91%  -7
PABR  AP 18 0021  BKN038 BKN050              5 BS-      16  12 20017     925  84%  -1
PABR  AA 18 0053  BKN032 OVC041              5 BS-      16  14 20018     925  92%  -1  28
PABR  AP 18 0115  FEW041 BKN049 OVC090   2 1/2 BS-      16  12 20019     924  84%  -2
PABR  AP 18 0128  BKN060 BKN085              5 BS-      16  14 20020     923  92%  -2
PABR  AA 18 0153  SCT070                     5 BS-      16  13 19018     923  88%  -1
PABR  AA 18 0253  FEW080 OVC200              5 BS-      15  12 20020     922  88%  -3
PABR  MA 18 0353  BKN075                     5 BS-      14  11 19016G22  922  88%  -3
PABR  AA 18 0453  SCT075                     7          11   8 19018     921  87%  -8
PABR  AP 18 0551  BKN080                   3/4 BS-F     12  10 19018     921  91%  -7
PABR  AA 18 0553  BKN080                   1/2 BSF      13  11 19020G23  921  91%  -6
PABR  AP 18 0555  BKN021 BKN035 OVC045     1/4 BSF      14  12 20020G25  921  92%  -5
PABR  AP 18 0604  BKN026 BKN036 OVC047       3 BS-F     14  12 20020     921  92%  -5
PABR  AP 18 0613  BKN013 OVC036            1/4 S+BS     14  12 20018     922  92%  -4
PABR  AA 18 0653  BKN037 OVC048              1 S-BS-    13  12 21018     922  96%  -5  26
PABR  AP 18 0732  OVC075                     3 BS-      10   9 21020     923  96% -10
PABR  AA 18 0753  OVC075                 1 1/2 BS-      11   9 22022     922  91%  -9
PABR  AA 18 0853  BKN075                     3 BS-       8   6 21021     923  91% -13
PABR  AP 18 0925  BKN075                   1/2 SBS      10   9 21025G30  924  96% -12  30
PABR  AP 18 0938  BKN075                   1/4 S+BS     10   9 21027G32  924  96% -13  32
PABR  AA 18 0953  BKN075                   1/4 S+BS     11  10 22024     924  96% -10  32
PABR  AP 18 1000  BKN007 OVC019            1/4 S+BS     10  10 23026     924 100% -12  30
PABR  AP 18 1039  BKN006 OVC026            1/4 S+BS     10   9 24024G34  926  96% -12  36
PABR  AP 18 1043  BKN010 OVC026            1/4 S+BS     10   9 23027G34  926  96% -13  36
PABR  AP 18 1122  BKN010 BKN019 OVC028     1/4 S+BS      9   7 24027G34  928  91% -14  34
PABR  AA 18 1153  BKN014 OVC019            1/4 S+BS      8   5 24025G33  930  87% -15  34
PABR  AP 18 1201  BKN014 OVC019            1/4 S+BS      7   5 24026G33  931  91% -16  33
PABR  AP 18 1217  BKN014 OVC038            1/4 S+BS      7   5 24024G34  931  91% -16  34
PABR  AP 18 1232  BKN014 OVC038            1/4 S+BS      7   3 24031G38  932  83% -18  38
PABR  AA 18 1253  BKN009 OVC021            1/4 S+BS      6   3 24028G34  933  87% -18  38
PABR  AA 18 1353  BKN015 OVC025              1 BS-       2  -2 25022G30  938  83% -22  35
PABR  AA 18 1453  OVC021                   3/4 S-BS-     0  -4 26022G31  941  83% -24  34
PABR  AP 18 1525  BKN025 BKN032            1/4 S+BS      0  -6 26026G33  941  75% -26  33
PABR  AP 18 1544  BKN012 OVC030            1/4 S+BS      0  -4 25024G31  943  83% -25  33
PABR  AA 18 1553  BKN012 BKN021 OVC035     1/4 S+BS     -1  -5 25024G33  944  83% -26  33
PABR  AP 18 1620  BKN012 BKN021 OVC050     1/2 SBS       0  -6 25023G32  945  75% -25  32
PABR  AP 18 1637  BKN012 BKN021 OVC050     1/4 S+BS      0  -6 25029G34  946  75% -27  38
PABR  AA 18 1653  VV014                    1/2 SBS      -1  -5 25021     947  83% -25  38
PABR  AP 18 1728  BKN025 BKN033            1/2 BS        0  -6 26020     948  75% -23  33
PABR  AA 18 1753  BKN047 BKN130              2 BS-       0  -7 25020G30  949  71% -23  33
PABR  AP 18 1804  SCT055 BKN130              4 BS-       0  -8 24020G26  949  68% -23  26
PABR  AA 18 1953  FEW055 BKN150             10          -2  -9 25018     952  71% -25

While I find clouds fascinating, there is nothing like the clear blue sky, and when the sky is clear in Alaska, and especially Southeast Alaska, it is very clear and very blue thanks to the clean air. This photo was taken on the 17th from Haines looking across Lynn Canal at Santa Claus Mt. (can you spot Santa lying down with his feet to the left and his head as the summit? Click on photo for a larger version)

Much of Alaska has been seeing blue over the last couple of weeks. An upper level ridge over the Bering Sea has kept the active, transitory storms to the far west. I added “transitory” because we are not without active weather, it is just active and static. There has been a strong low in the Northeast Pacific for at least two weeks with strong offshore flow almost uninterrupted for the southeast and south coast. Here’s three representative surface maps, from Dec 6, 13 and 18.

In between those dates the low has looped north close to Prince William Sound and been fortified by absorbing other lows, but essentially it is the same low, powered by the contrast between the relatively warm water of the North Pacific and the cold air coming over the upper level ridge and off the cold land mass of Alaska.

Alaska: an astronomy hotspot?

While this pattern has opened up the skies, especially clearing out cloudy Southeast, it comes at a cost. It’s been brutally cold in the interior: –60F/–51C this morning in Fort Yukon and plenty of sub –40F/C lows around the interior. Coast dwellers don’t get that cold, but we have similar downward deviations from the “normal” temperatures and often lots of wind. Who’s got it worse? This is one reason I’ve never thought of Alaska as a stargazer’s paradise. When we have the clear weather its either too light (summer) or awfully cold (winter). Autumn tends to be quite cloudy, although sometimes we get a lucky string of nice weather, as we did this September. We also had some breaks this August at a perfect time to see the Perseids meteor shower. There are some serious astronomy buffs up here though who don’t want to hear this negative talk. There are even some in Juneau, and they have made the best of it, in part by operating the Marie Drake planetarium. The Planetarium, opened back in 1968, features a 30 foot domed ceiling and a powerful projector. (If you are an Alaskan, you know that Marie Drake wrote the words to the Alaska Flag song, which begins, “Eight stars of gold” and features the Big Dipper and the North Star.)

Lunar eclipse on the 20th perfect for Alaska viewers

click for full graphic.

So, to be more upbeat, there are some wonderful astronomical sights to be seen in the northern skies (not to mention the aurora borealis). One of them will be the total lunar eclipse this coming Monday night, Dec 20th (Alaska Time). Alaska (and all of North America) is on the best part of the globe for viewing this eclipse. The moon will be well up in the sky, clear of the mountains, and you don’t have to stay up super late. The first part of the eclipse (penumbral) starts at about 8:30 pm AST, gradual darkening the disk with a copper coloration. At the about 9:30 pm AST the umbral phase begins, and the disk will darken more dramatically, first a bite from the side, then the whole disk or totality. The total phase lasts over an hour from 10:40 to 11:54 pm, then the reverse sequence occurs. To add to the spectacle, the moon will be just above the wonderful winter constellation Orion. And to be even more upbeat, the weather looks like it should be pretty clear for much of Alaska. Check the latest forecast for your area, and don’t forget to bundle up well.

Eclipse links:

Mr. Eclipse (Fred Espenak)
Naval Observatory Eclipse Portal

NASA eclipse info
Space Weather dot com