889 
fxak68 pafc 211424 
afdafc 


Area forecast discussion 
southcentral and southwest Alaska 
525 am akst Sat Nov 21 2009 


Analysis and upper levels... 
in the upper-levels a trough is present over the Bering/Aleutians and 
over the Gulf of Alaska...with a ridge nestled in between through SW Alaska 
and the akpen. A shortwave is traversing Bristol Bay and moving 
northeast towards the Susitna Valley. At the surface a low south of 
Middleton Island in the Gulf of Alaska is moving east and filling. A 
series of storm-force lows are in the Bering Sea. One low just north 
of Attu is moving southeast and filling. The other which is just 
north of Atka is moving east and slightly deepening. 


Model discussion... 
models are satisfactorily capturing the major features across the 
aor. The low south of Middleton Island this morning will continue to 
move east and weaken...eventually dissipating over the southeast Gulf during 
the day Sunday. The weakening low over the far western Aleutians will 
move southeast today and dissipate as it slips into the North Pacific 
early Sunday morning to the west of Adak. The other low to the north 
of Adak this morning will move east and approach the coast of Bristol 
Bay on Monday. The energy from the dissipating low over the western 
Aleutians looks to help deepen the trough in the Bering...and also 
slightly deepen the low headed towards Bristol Bay. A storm force low 
is developing over the North Pacific...and models move this into the 
southern Gulf Sunday night and up towards the Kenai Peninsula on 
Monday. NAM appears a bit of an outlier in rotating it up too far to 
the east. Morning forecast package leans more on the GFS through the 
Middle-Range period with a transition to the ec for the long term period 
based on satisfactory initialization and consistency. 


Short term forecast... 
southcentral... 
light snow through the Matanuska Valley and Anchorage bowl Saturday 
as shortwave approaches from the west...and then tapering off as the 
moisture from the feature moves east into the Copper River basin and 
Prince William Sound Saturday evening. A steadier precipitation looks 
to overspread Kodiak Island and upslope areas of the Susitna Valley 
on Sunday as moisture ahead of the storm-force low moves into the 
zone. Warmer air with this low will transition snow to rain along 
coastal areas of the Kenai Peninsula...eastern Kodiak Island and 
Prince William Sound as the precipitation continues Sunday into 
Monday. Easterly 850 mb flow will help to downslope and retard 
accumulating snows over the Anchorage bowl and mat-su valley on 
Sunday and Monday...with mostly cloudy conditions expected with 
perhaps a few flurries or brief snow showers. 


Southwest... 
snow and rain with the low rotating through the central and eastern 
Bering. Arctic air still predominant over the kuskowim Delta/valley 
and interior Bristol Bay where snow looks to overspread from west to 
east Saturday night into Sunday. Strong winds along the northern 
periphery of the low will aid in blowing snow...which combinded with 
the falling snow may yield blizzard conditions along the kuskowim 
Delta coast overnight Saturday through early Sunday. In the warmer 
air further south...snow will mix with and change over to rain across 
the akpen as the system works east...and then transition to snow 
again as the remnant low enters Bristol Bay on Monday. 


Bering Sea/Aleutians... 
numerous rain and snow showers in the wake of the Bering lows over 
the region. Storm-level winds diminishing over central and western 
marine zones Saturday evening as the far western Bering low weakens 
and dissipates. Rain/snow overspreading the pribiloffs...Saturday and 
transitioning back to snow/snow showers as the low passes to the 
south. Gusty north-northwest winds aiding with areas of blowing snow 
through Monday...though with less available precipitation...believe 
conditions will not reach blizzard criteria with this system over the 
pribiloffs. 


Long term forecast... 
staying active in the Gulf and Bering through late next week as 
progressive pattern establishes over the aor. Forecast confidence in 
the long range remains poor due to timing issues with systems and 
less than stellar model consistency. More seasonable temperatures 
however as Arctic air remains over the interior of Alaska. 


Aer/alu...watch/warning summary 
public...blizzard watch...155 
marine...storm...352 172 175 176 
gale...351 412 413 414 150 155 160 165 170 171 179 180 185 
heavy freezing spray...160 180 185 


Jam Nov 09 

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