Levi Cowan has been tracking tropical systems since 2002, and is currently working on his bachelor's degree in physics at UAF.
By: Levi32, 5:53 AM GMT on November 28, 2007
A major pattern change is beginning, not just for Alaska, but for the rest of the US as well. A sudden pulse of the SOI is partly to blame for this, although La Nina remains firmly in place across the tropical Pacific. A strong low currently south of the Kamchatka Peninsula in Russia will be moving into the Bering Sea during the next couple days. An enormous ridge will build ahead of this low and up into Alaska, bringing very warm air and clear skies ahead of the low. Temperatures will be running 15-20 degrees above normal for about 4 days as this ridge sits overhead. At the same time as this ridge moves in, cold air will be massing over Canada and pouring into the US plains, feeding a potentially potent snow storm for the eastern seaboard. Over the course of the following week, that cold air will make it's way west into Alaska, nudging out the ridge. The ridge will split leaving a blocking anticyclone over NW Alaska that will slowly retreat towards Asia. This is key because blocking highs in that position force lows south of them to come underneath before turning north. This means that lows that would typically curve north well west of Alaska will have to pass underneath the block and much further east before coming north. As the cold air takes a foothold in the interior of Alaska, the storm track will be simultaneously directed into the gulf. The GFS has been hinting consistently at a strong sub-970mb storm in the gulf next week running right up against that cold air. This would be a major snow event over a large area if this plays out.
This general pattern with a more south and east storm track and lots of troughiness over the Gulf of Alaska will be the story for most of December. The pattern for the lower 48 will start cold in the plains to the eastern seaboard but rapidly reverse with a strong warm ridge setting in as the dominant pattern for much of the rest of the winter.
We shall see what happens!
GFS 168 hour forecast showing a potential snowstorm for southern Alaska.
Updated: 5:57 AM GMT on November 28, 2007
By: Levi32, 5:04 PM GMT on November 24, 2007
The temperature last night dipped below freezing just long enough to give us an inch and a half of wet snow. Sadly this snow is going to melt(again) with another storm system bringing warm air into the region early next week. A strong low and associated occluded front in the western Bering Sea is slowly weakening and drifting east. A triple-point low formed south of the Aleutians east of the parent low last night, and will rotate northwest over the next couple days, bringing light rain to the Pribilof Islands and SW mainland.
A new low is forming on the cold front south of the triple-point system. This new low is positioned under a very strong jet, and will strengthen rapidly as it moves northeast today and tomorrow. By Monday the GFS has it east of Kodiak with a pressure in the 960s. This low has another load of tropical air with it, and precipitation will be all rain along the coast under 5000 feet. More wind is likely with this system, but nowhere near as bad as the last storm.
We shall see what happens!
A triangle of lows approaches Alaska. The southernmost low on the map is the new one forming on the cold front. The one directly north of that is the triple-point low, and the low west of that is the parent low that started the whole thing. The Alaska mainland is in the top right corner. (Satellite background image credit: Dundee)
Current surface map:
^Click for Loop^
Updated: 5:05 PM GMT on November 24, 2007
By: Levi32, 4:53 PM GMT on November 22, 2007
What was supposed to be a routine melt-down storm this week has turned into a pretty nasty situation. For 3 days heavy rains have been melting snow and swelling streams, and a flood advisory is now in effect for the Anchor River and Homer area, where I live. Now this morning winds have been added at an alarming rate. Take a look at the surface map at the bottom of this blog entry and look just to the right of the middle. You will see the long fetch of warm air from the southeast pouring into the warm sector of the low over my area. The gradient is extremely tight, and amazingly the winds in the warm sector are exceeding the winds on the back side of the low, which in the north Pacific is very rare. At my house the winds are blowing foam insulation slabs and sawhorses everywhere lol. We just had a wind gust of 105 mph, so things are pretty dangerous outside. Power is fluctuating as you can imagine, and I wouldn't be surprised if we black out any second. The winds aren't sustained at more than 30mph, but the sudden gusts of Cat. 2-3 hurricane force are what really shake the place. Hopefully power will stay on or we'll have a lot of uncooked turkey's around here this Thanksgiving lol.
To those of you who thought Alaska was safe from hurricanes, you thought wrong lol :)
^Click for Loop^
Updated: 4:58 PM GMT on November 22, 2007
By: Levi32, 3:31 PM GMT on November 13, 2007
The model consensus has shifted much further south and east with the gulf low on Thursday and Friday. The feeling now is that this is a southeast panhandle problem, and won't be affecting south-central too much. However, we are far from out of the woods snow-wise this week. The system in the Bering Sea is preparing to move ashore in Bristol Bay, and is a highly convective low, meaning that it's fueled entirely on arctic air. Lows like this can produce copious amounts of snow if they sit in the same area. You can see it as a big popcorn-like structure in the center of the satellite image at the bottom of the blog entry. If you can see the land border well enough you'll see that it is almost ashore in Bristol Bay. Precipitation started making it north east of the Alaska range last night, but so far only a dusting has fallen at my house and not much more anywhere else. Later today the main convective zone will move over and we will get our dose of white. SW Alaska is getting dumped on right now, with some coastal areas changing over to rain. This will continue to be the case through tomorrow. This low will slowly drift east and end up in the western gulf by Friday. At this time former TS Tapah, the big storm, will be moving through the extreme SE gulf. One thing this storm will still be able to do is throw subtropical energy north into the Bering Sea low, further aiding precipitation and extending the life of the low by keeping a strong temperature gradient.
A new pattern is shaping up over the Pacific, and this trough will be sitting in our area for some time after this week is over. The models are very unreliable past day 5 in this type of pattern, so there is much to be worked out. For the rest of this week southern Alaska will see lots of snow flakes falling as the trough lurks around. Today I expect anywhere from 4-8 inches of snow in most places, with the exception of Anchorage and the Mat-su until they can overcome the rain shadow tomorrow. Areas of the north gulf coast such as Valdez could get some significant totals if it doesn't change over to rain. By Friday and Saturday the monster low in the SE gulf will make its closest approach to us as it drifts northwest and weakens. It will get close enough to deliver some pretty brisk winds, and will probably add to the moister and precipitation one way or another. Beyond this weekend the models are askew, and we'll just have to see what happens!
^Click for Loop^
Updated: 4:22 PM GMT on November 13, 2007
By: Levi32, 4:11 PM GMT on November 12, 2007
This morning's NWS discussion:
".LONG TERM FORECAST...
ON THURSDAY A LOW IN THE SUB TROPICAL JET WILL REACH THE COLD AIR
ASSOCIATED WITH THE LARGE BERING/NORTHWEST GULF LOW AND EXPERIENCE
EXPLOSIVE CYCLOGENESIS. THIS LOW WAS A TROPICAL DEPRESSION SOUTH OF
JAPAN YESTERDAY AND THUS THE "BOMB" SCENARIO LOOKS REASONABLE.
NUMERICAL MODELS ARE STILL FIGURING THIS LOW OUT...BUT LOOK TO BE
TRENDING TOWARD A POSITION IN THE EASTERN GULF WHEN IT IS AT ITS
DEEPEST THURSDAY NIGHT. THE LOW WILL THEN MOVE NORTHWESTWARD TOWARD
SOUTH CENTRAL ALASKA BY THE END OF THE WEEK. WORTH WATCHING THIS
STORM AS HURRICANE FORCE WINDS ARE POSSIBLE WITH IT.
MARINE...GALE WARNING 120 150 155 160 165 170 172 175 179 185.
LUDWIG NOV 07"
Models are still on tap for a major low entering the Gulf of Alaska in 3-5 days. Tropical Storm Tapah and associated subtropical air will collide with a mass of Siberian arctic air, causing very explosive cyclogenesis and the "bomb" scenario. In Alaska the "bomb" is not any less of a bad thing as it is in the lower 48, despite the fact that people believe we should be "used" to them. Like the recent European storm, this will be a very bad situation for ships in the area, and what you might call a storm surge will be battering the coast for miles, although the threat of coastal flooding is minimal in this part of Alaska.
The track of this storm will be crucial to snow amounts in certain areas. Everyone is going to get the wind as the size of this thing will be huge. The GFS has been trending further east and south with this over the last couple runs, and the NWS as usual is following suit with their forecast. The NOGAPS and UKMET are the northerly models right now, which still take the low up east of Kodiak Island, meaning more snow for southcentral. All these solutions I expect to swing around a bit over the next few runs, as this is a very delicate situation that could unfold a number of different ways. The GFS seems to want to shove most of the energy eastward and out of the picture, while other models allow the low currently in the Bering Sea to pull the energy north, as in the figure below:
In the above image, the low is in the process of deepening and is still quite far south. The trough extension to the north of the low is what used to be the Bering low, which came east near Kodiak Island. This extension north is what could draw the energy closer to the coast, as some of the models are suggesting. Also evident in the image is the huge convergence boundary between warm and cold air setting up in the gulf. Lots of overrunning snow can be expected under that strong warm front. Bottom line this will be a very strong and dangerous storm and it's winds will be felt everywhere. Where the snow falls is entirely dependent on track, which is still to be determined.
The Bering Sea low that I mentioned above is currently strengthening and moving towards the SW coast today. This is going to provide us with several inches of snow in the 2 days prior to the big cheese. Snow lovers are really happy this week :)
We shall see what happens!
This image shows how TD 22w(now TS Tapah) and other ingredients are starting to come together to set up explosive development in 3 days. (Satellite image credit: Japan Meteorological Agency)
GFS phase diagram for the gulf storm. The intensity and size are notable, along with what appears to be a warm-seclusion scenario at peak intensity.
^Click for Loop^
The 986mb wave on the cold front of 976mb low in the above map is the disturbance moving east that will bring us some snow over the next couple days, and will also play a part in the gulf storm's track. The 988mb low on the western edge of the image is the low currently absorbing TS Tapah east of Japan.
Updated: 4:50 PM GMT on November 12, 2007
By: Levi32, 6:16 PM GMT on November 11, 2007
A severe and potentially life-threatening weather event is shaping up this week for southern and southeastern Alaska. The trough which brought us 8 inches of snow yesterday will move out and be replaced by a weak ridge today, followed by a shortwave tomorrow. Under this shortwave a weak low will cross the Bering Sea from the west spreading light snow over western and southern Alaska Tuesday and Wednesday. This low will be dragging a lot of cold Siberian air with it, and the polar jet will dip quite far south as the low moves east.
What is now TD 22w in the west Pacific will be nosing into our vicinity in 3-4 days, converting to extra-tropical as it goes. This system, having originated from the tropics, will have a strong sub-tropical connection as it moves north. This mass of warm air will collide with the cold Siberian air in the Bering Sea, causing explosive cyclogenesis in the Gulf of Alaska. Here's what this morning's NWS discussion had to say:
"Long term forecast...
the Bering Sea low will continue to move southeast setting up what
looks like a major Gulf storm later in the week. The upper low will
pull cold air off of Siberia in the polar jet. This will consolidate
with the subtropical jet...which currently has a strong tropical
connection. Indeed...what is at least a tropical storm (possibly a
typhoon...I have not had time to explore this more fully) will go
extra-tropical and move into the Gulf of Alaska and undergo
explosive cyclogenesis as it inhales the siberian air. Many ensemble
members show a surface low in the 940s by 18z Thursday...and the 00z
run of the GFS drops the surface low to 937 mb. With this sort of
strength and development hurricane force winds would be likely.
Exact timing and location are still in question of course...but a
major event is shaping up for later in the week somewhere in the
Ludwig Nov 07"
As Ludwig said the models are jumping all over the intensity and size of this system. A large radius of 80+ knot winds on the back side of this monster is likely. As far as track goes, the GFS keeps the low just far enough south in the gulf to spare the coast a major snow dump, and splits a piece of the energy in the form of a secondary low to the southeast. The southeast panhandle will get the full brunt of the storm with this scenario. The ECMWF, CMC, and Japanese models move the low further north, increasing snow chances. The ECMWF really wraps this up, pulling the secondary low right up into Prince William Sound, which is the classic position for a major snow event over Anchorage and the Kenai Peninsula. Within the next few days the position and track should be narrowed down, but regardless of where the snow gets dumped, the wind radius of this will be massive, and everyone is going to feel it. Bottom line is we're looking at possibly one of the biggest storms we will see this winter, and conditions could become life-threatening in some areas during the course of the storm.
We shall see what happens!
This image taken this morning shows TD 22w being caught up by an extratropical low on its way east. This storm will eventually end up in the Gulf of Alaska as our big cheese later this week. (image credit: Japan Meteorological Agency)
Updated: 6:30 PM GMT on November 11, 2007