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Area forecast discussion 
southcentral and southwest Alaska 
100 PM akdt sun Mar 14 2010 


Analysis and upper levels...a high amplitude pattern is in place 
with troughs centered over eastern Russia/far western Bering and 
Mainland Alaska/Gulf of Alaska...and ridges over the central Bering 
and Canadian rockies. Both of these ridges are amplifying as the 
troughs dig southeastward and this is slowing down the eastward 
progression of these troughs and ridges. The major Aleutian low 
from the past few days has now evolved into a complex low...with 
two main centers over the southern Gulf and another further south. 
The occluded front has moved to southcentral bringing snow primarily 
to Prince William Sound and the Cook Inlet region. Offshore flow 
has limited snowfall in many places such as Anchorage...the 
Matanuska Valley...and Valdez by maintaining very dry low level 
air mass resulting in a lot of virga. This flow has weakened and 
low levels have moistened a bit...so expect to see a little more 
snow reaching the ground this afternoon as bands of snow continue 
to move across the area. Strong northerly winds are producing the 
usual blizzard through Thompson Pass...but conditions will improve 
later this afternoon as winds diminish. 


Cold advection on the back side of the system continue to produce 
snow showers...blowing snow...and frigid temperatures across the 
eastern Bering region. Blizzard conditions...which began 
approximately 30 hours ago...persist across the southern Alaska 
Peninsula. With the Bering Sea ice pack not too far north of Cold 
Bay (approximately 20 miles) the southern peninsula is observing 
Continental like weather with temperatures in the single digits. 
An upper short-wave trough is moving across the peninsula now 
with upper ridge right behind it...so conditions are improving 
from west to east across the eastern Bering. 


Model discussion...solutions continue to vary with waves forming 
along the Bering front tonight through Monday night. The 12z European model (ecmwf) 
is the most aggressive in developing one of these lows as it moves 
up the front Monday night and Tuesday. Since none of the models 
have very good run-to-run consistency with this will go with the 
majority solution of weak frontal waves without further development. 
Otherwise...models are in fair agreement with major features in 
the short-term. 


Short term forecast... 


Southcentral Alaska...the occluded front will dissipate this 
afternoon. However...upper waves rotating around the Gulf low 
will continue to produce showers through Monday night...especially 
along the coast. The Bering ridge will then build over Mainland 
Alaska Tuesday and Wednesday which will push the Gulf low off 
to the south and set up dry weather across southcentral. There 
may be a weak northerly wind event in the usual places Tuesday 
night and Wednesday as the pressure gradient tightens and colder 
air moves down the east side of the ridge. 


Southwest Alaska/eastern Bering...snow showers and strong winds 
will finally come to an end tonight into Monday as the ridge 
moves to the eastern Bering and western Alaska. This ridge will 
strengthen and become cut-off over western Alaska Tuesday...ensuring 
a period of dry and calm weather across the region. 


Bering Sea/Aleutians...the strengthening ridge will serve to block 
storms out west from progressing beyond the central Bering. In 
fact...major storms will remain west of the forecast areas the 
next few days...rotating around a large low over eastern Russia. 
Fronts extending from these lows will move across the western 
Bering and Aleutians and then stall and weaken over the central 
Bering. 


Long term forecast...medium range models have now come into good 
agreement in evolution of the blocking ridge the end of next week. 
It will move over the northern Mainland middle week and then phase 
with ridge along western North America coast at the end of the week. 
This will allow long-wave trough to set up from the southern 
Mainland westward across the Bering. So...dry weather will persist 
through middle week over the Mainland with storms confined to the 
Bering and Aleutians. Weather will then become more active at the 
end of the week as storms move up the western side of the ridge 
to Mainland Alaska. 


Aer/alu...watch/warning summary 
public...Blizzard Warning 131 181. 
Marine...Gale Warning...130 132 150 155 160 170 172 175 176 179 185. 
Heavy freezing spray warning...130 132 138 140 141 150 155 
165 170. 
Fire weather...none. 


Seb Mar 10 

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