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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

Everything is bigger and more powerful in Alaska. Well, most things anyway. Certainly weather. While some folks were marveling at and bickering over a Midwest low pressure system that bottomed out at 955 mb in Minnesota a few weeks ago there were several of about that depth passing through the last frontier and one since with a central pressure of 939 mb a little south of the Aleutian chain. However, it is important to know that the actual pressure value of a storm is not what makes it strong or weak, but the difference in pressure over a distance, or the pressure gradient. The pressure gradient can easily be seen on a surface map like the one below. (click for larger version in new tab or window)

Do you see the 1013 mb low just south of Cordova, and the 998 mb low up in eastern Siberia? Without the chart to look at one might think of lows with that kind of wimpy central pressures to be wimpy themselves. Not so here. The reason is the super strong 1052 mb high in between the two. Look at how the isobars are packed close together in the western Bering Sea and on north into Russia. The closer the isobar spacing the stronger the gradient. The pressure gradient is a force acting on the air. It and other factors (such as friction) determine the wind. Winds over the ocean there are 30-40 kts sustained.

Alaska’s bigger and more powerful winds

Let’s shift to mainland Alaska where the gradient between the super high Bering high and not-so-low Cordova low is bunched up along the arc of (big, powerful) coastal mountains known as the Alaska Range and Chugach Mountains. It is no coincidence that the gradient is bunched up there—it is because the air bunches up there, just like water bunches up above a dam. Water and air both obey the laws of fluid dynamics. Think about the water above a dam…slow, right? What about if the water overflows the dam or if there is a break in the dam? There is a big, powerful acceleration at that point. But the atmosphere is way deeper than even Alaska’s mountains, so how can the analogy hold…the dam is not high enough to block the flow, right? It holds because in Alaska’s big, powerful winter there is a usually a deep layer of cold air near the surface that is extremely dense compared the air above it (which means it is stable, it resists moving up into or mixing with the air above it). Think of molasses flowing under a layer of cooking oil. If it is pushed up a mountain slope by high pressure and tops the dam or finds a break, the pent up force is released and acceleration results. This is the genesis of Alaska’s many bigger, more powerful winds common to coastal mountains, and referred to variously as gap winds, down slope winds, williwaws, Chugach winds, Chinook winds, and Taku winds. These vary in scale but all can reach damaging velocities.

Act one has begun

Between the time of the map above (3am Tuesday) and as I write this (2pm) the winds have been howling in select places in Southcentral Alaska (select because of their proximity to the mountains and especially the gaps in the mountains). At Palmer the winds are gusting from the north at 40 to a bit over 50 kts with some blowing snow (and/or perhaps dust from the river valleys). If you are more familiar with miles per hour for wind speeds, remember the 7/8 rule, 7 kts=8 mph, and make an approximate adjustment from there. Prince William Sound blow holes are active with close to 50 kt gusts at Whittier and peaks as high as 74 kts at the Valdez airport. Cordova Airport is reporting gusts of 20-25 kts but just east in the Copper River Delta you can bet it is blowing at least 2-3 times that…the delta is one of those gaps, and yes, a big and powerful blow hole even for Alaska.

SE is next

Down here in Southeast Alaska we have more gaps and channels to funnel that cold, dense air than we can keep track of. They each have their favored pressure gradient orientation, adding yet more complexity. Skagway is windier on average than Haines, but right now Haines is a bit windier. Currently it’s gusts to 22 kts at the airport, but somewhere in the valley it must be stronger, since the area is filled with suspended silt, raised from the snow-free river bed (the automated wx station is reporting 1-1/4 mile visibility in Haze). Out at Eldred Rock, in the highly channeled Lynn Canal, north winds are presently sustained 30 kts with gusts to around 45. But the strong gradient is not here yet. Expect all these winds to about double by tomorrow. Take a look at the computer forecast surface chart to see why.

This is the same chart as the top one, surface pressure patterns, but also with color-coded temperatures (for a bit above the surface). It is forecasting the patterns for 9 am Wednesday. By this point the super high Bering high has stretched east through middle Alaska and on into the Yukon, and only weakened slightly. The Cordova low on the other hand has been assimilated into a pacific bomb that rushed the BC coast only to stall in Queen Charlotte Sound. This has set up an amazing 75 mb gradient between it and the Kluane, YT region, and will visit more wind power over the coastal area between the two extremes than mere humans will be able to calculate. The NWS has high wind warnings, or at least advisories, up for most SE communities, and gale or storm winds for virtually all the marine waters. Welcome to winter in Alaska.

The winter forecast, please

Speaking of winter I did promised an outlook for the whole winter, not just the next day. It’s coming this week. Stay tuned. Meanwhile, I’d love to hear your comments or questions on this or any story via the comment link below.

Yes, bomb is a technical term in meteorology. In a general sense it is a rapidly-strengthening extra-tropical storm (the common low pressure disturbances that regularly spread rain, snow wind etc across the mid latitudes), and as the name implies, with the capacity to do damage, usually via wind. Also implied is the element of surprise. To qualify as a bomb the central pressure must drop by 24 millibars in 24 hours. Our specimen is a low that made landfall in Southeast Alaska last week (10/12/2010). Lets see if it fits the general or technical criteria.

This infrared satellite image ought to at least suggest to the layman, and convince anyone with meteorological training that this was a powerful, well formed, yes, even beautiful storm. The spiraling frontal band wraps 1-1/2 times around a tight-looking low center a little northwest of Sitka. This photo does not tell us much about its life story, though, and we’re wanting to know if this storm is of the fast hitting variety.

For that let’s look at the surface chart (click for a larger version): The first one is from 4pm ADT on Monday the 11th. The low in question is labeled 1000 (millibars or mb for short). Its the one in the lower right part of the frame which happens to be straight west of Seattle and straight south of Anchorage, but is not aimed at either metropolis, but at the sparsely populated panhandle of Alaska.

Now, at 10 pm the low has moved northeast and deepened to 993 mb, a drop of 7 mb in 6 hours, a vigorous strengthening by most standards. But this is Alaska in October. Stay tuned…

At 4am the low has dropped to 976 mb. That’s a total deepening of the requisite 24 mb, accomplished in not 24 but 12 hours! The rapid deepening along with the fast movement of this storm meant that any mariner or landlubber in its path had rapid and major weather changes to deal with. It is a testament to the science that this storm was well forecast far enough in advance that mariners could seek shelter and landlubbers could make provisions. That might not have been the case 20 years ago.

For just one example of the rapid weather changes, check out the Sitka observations quoted below from the early morning to mid-day when the storm was hitting this coastal burg the hardest. At 5 am conditions were VFR with only 10 kts of wind. A little light rain was falling but, hey, when is it not? By noon the visibility is down to a mile in heavy rain and the wind is 23 kts with gusts to 57 kts, the next hour 64 kts (that’s 74 mph for your land lubbers or about 32 m/s for you scientists.)

Site M/A Day Time Sky Conditions           VIS Weather Temp DP Wind(kt)  Alt  RH  Chill Peak
PASI  AA 12 0253  OVC080                    10          48  40 13008     962  74%  44
PASI  AA 12 0353  OVC055                    10 R-       48  40 13013     955  74%  42
PASI  AA 12 0453  OVC055                    10 R-       49  39 11010     949  68%  44
PASI  AA 12 0553  BKN070 OVC090             10 R-       48  37 11015G22  942  65%  42
PASI  AA 12 0653  OVC060                    10 R-       50  36 10013G24  930  58%  45
PASI  AA 12 0753  OVC046                    10 R-       50  38 11025G36  917  63%  42
PASI  AA 12 0853  OVC042                     9 R-       49  40 10018G32  908  71%  42
PASI  AA 12 0953  BKN036 OVC050              6 R-       49  42 12016G26  906  77%  43  30
PASI  AA 12 1053  BKN041 OVC048              4 R        49  43 12013G20  906  80%  43  28
PASI  AP 12 1146  FEW028 OVC038              2 R        50  45 14028G37  910  83%  42  40
PASI  AA 12 1153  SCT024 BKN034 OVC042   1 1/2 R        50  44 15023G45  911  80%  43  45
PASI  AP 12 1201  FEW020 BKN029 OVC035       1 R+       50  45 15029G57  912  83%  42  57
PASI  AA 12 1253  BKN025 OVC030          1 1/4 R+       49  44 16036G64  921  83%  39  64
PASI  MA 12 1453  BKN035 OVC043              5 R        50  42 16036G58  932  74%  41
PASI  AA 12 1853                             3 R-F      49  45 19022G32  958  86%  41

Other land stations fared similarly, with automated marine observations at exposed locations clocking 65-90 kts (75-100+) and the high elevation station on Sheep Mountain, near Juneau hitting over 100 kts (120 mph). Here are some specifics:

Metlakatla: peak wind 55 mph. Ketchikan: peak wind 60 mph, and around 2 inches of rain. Hydaburg:  peak wind 70 mph. Port Alexander:  peak wind 69 mph. Little Port Walter: 2.85 inches rain in 24 hrs. Hoonah: 2.55 inches rain in 24 hrs. Juneau: peak wind 68 mph; power knocked out in some areas due to trees on power lines. Pelican:  peak wind 71 measured by the Pelican Elementary School station, plus 4.46 inches of rain in the 24 hrs up to 8 am on the 13th (a record for that date but by no means for the the month or year). Skagway:  peak wind 54 mph.

Coastal marine observation stations are automated weather stations (for reasons which will become obvious) placed at  locations pertinent to marine interests. Usually they have a much higher wind exposure than inhabited places—in some cases they are in locations with highly accelerated winds due to channeling by terrain. Here are some of the more extreme examples out of the SE AK marine obs. These kind of winds are not all that uncommon at these stations.

Cape Decision:  peak wind 74 kts. Sisters Island:  peak wind 67 kts. Cape Spencer: peak wind 86 kts. Eldred Rock: peak wind 64 kts. Lincoln Rock: Winds hit 87 kts then the wind speed went missing for seven hours, coming back online after the height of the storm.

Ocean (or moored) buoys are faithful and indispensable reporters of the weather off the coast. Most of these are away from the small scale channeling effects of the terrain, and may seem understated compared to the coastal marine obs that rack up the wind speeds like those above. You have to read them with that in mind. You can also look at the size of the waves reported in a storm to get a reality check. Here’s a plot of pressure, sustained wind speed and gust speed at buoy 46084, the Cape Edgecumbe buoy, located about 50 miles SW of Sitka, just south of the low’s track. Note the hurricane-like pressure fall and rise on 10/12, and the attendant winds. Significant wave heights were over 30 ft at this buoy near the time of the highest winds. The wind scale is in meters per second (m/s). Double it if you want knots, add another 15% to go to from knots to mph:

If you are interested in seeing where these coastal stations are located, or getting the data for them, visit the National Data Buoy Center’s excellent web site at http://www.ndbc.noaa.gov/maps/Alaska.shtml.

I’d love to hear any first hand accounts of this storm (mariners and landlubbers welcome). Use the comment form for that or any questions, or suggestions for topics to cover. I’m still working on an outlook for coming winter and hope to post it next week.

After a once-in-a-decade-or-more dry spell for 2/3rds of Alaska the weather machine in evening the score. Here in Haines we enjoyed 12 straight days with no precipitation and some record warm afternoons (and, yes we did get the hay cut, dried and into the barn, but it did take 5 days to dry. See the hay-cutting-weather post). This was the general case for all of normally-wet Southeast, Southcentral (Anchorage’s drought was broken a up by several days of “trace” amounts of precipitation—if you ignore those they had a 19-day rainless period), and right on into the interior where Fairbanks had 21 consecutive dry days (no traces even). Of course Anchorage is normally quite a bit drier than Southeast, and the interior drier yet. So compared to climatology, the September 2010 dry spell award should go to Yakutat, where the average September doesn’t see more than 8 dry days, consecutive or not. This year there were 14 in a row (by the way, that was it, 14 dry days total!).

Well, on September 23rd the switch was flipped, the omega block gave up, and the low pressure systems started a rampage that is just slowing a bit now, but not stopping. The first weather system was an especially strong one for so early in the storm season…or for any season. The infrared satellite image below shows a vigorous front blasting through Southeast AK, while the low center (looks like a hook or almost an eye) hangs offshore about 100 miles south of the coast with heavy convective cells rotating around the south side of it:

Below is the surface analysis for a few hours earlier, showing the tightly wrapped isobars:

The storm was at its lowest central pressure at this point, a very low 953 mb. It slowly weakened over the next couple days, but it still had enough strength to wreck havoc from British Columbia to the Alaska Range. Marine areas were hit with winds up to 90 mph. Many parts of Southcentral AK also had high winds, due to the strong pressure gradient from the interior to the Gulf of Alaska, and the acceleration of the wind squeezing through mountain passes (the Venturi effect). Here are some specifics from the NWS:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
545 PM AKDT FRI SEP 24 2010

...WIND REPORTS FROM ACROSS SOUTHCENTRAL ALASKA...

THE HIGHEST WIND GUSTS RECORDED TODAY AS OF 5:30PM ACROSS
SOUTHCENTRAL ALASKA.

-------------------------------------------
    SITE                            GUST
-------------------------------------------
BETWEEN WASILLA AND PALMER         78 MPH
VALDEZ AIRPORT                     62 MPH
PALMER AIRPORT                     61 MPH
ANCHORAGE INTERNATIONAL AIRPORT    59 MPH
WASILLA AIRPORT                    52 MPH
MERRILL FIELD IN ANCHORAGE         48 MPH
KENAI AIRPORT                      46 MPH
TALKEETNA                          44 MPH
SOLDOTNA                           28 MPH

STRONG WINDS WILL CONTINUE INTO THE EVENING HOURS...WITH AREAS OF
REDUCED VISIBILITY IN MANY PLACES DUE TO BLOWING DUST.

Since this first storm broke down the gates, there has been a new assault every few days, and most coastal areas are about to surpass the dry spell with an equal or longer wet spell. In actuality, this is much more typical than the dry spell. The main thing that stands out now is that the strength of many of these lows is quite impressive for early October.

What’s next?

Does this progression mean anything? Will it continue? Beyond the 5-10 days (variable) of useful forecasts from the computer models (which right now are calling for a continuation of the current storm cycle), we enter into the realm of general, broad brush forecasts of whether it will be wetter or direr than normal, warmer or cooler etc. averaged over a time period. There is not much to go on, but making some statistical associations with longer-term climate and oceans cycles (such as El Nino and La Nina among others) may have some validity and possible usefulness in predicting what kind of winter we might have, for instance. Am I bold enough make that kind of forecast? Check back around the middle of this month to find out.