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Area forecast discussion 
southcentral and southwest Alaska 
200 PM akst Friday Nov 20 2009 


Model discussion...model initializations and forecast trends through 


Sat night are in good agreement. Problems arise after this as the NAM 
becomes the outlier with the next storm to enter the Gulf of Alaska. 
The GFS model is converging toward the 00z European model (ecmwf) solution by bringing 
a strong low center into the Gulf of Alaska Sun night. By Monday 
afternoon the 12z European model (ecmwf) carries the center into the interior...which 
is a departure from the ooz run which holds the center in the western 
Gulf. The 12z GFS tended toward this position...so will continue with 
that trend of the 00z European model (ecmwf) and 12z GFS. Confidence is fairly low in 
the long term as models vary considerably. 


Upper levels... 
the pattern becomes somewhat more amplified in the NE Pacific and 
Alaska over the next couple of days. The long wave along the western 
US moves east as ridge build over the eastern Gulf and central 
Mainland sun evening. The low over the Mainland retrogrades to south of 
the Gulf of Anadyr Sun night. Stacked center over the western Bering 
Sea weakens as developing wave south of the western Aleutians moves 
to over western Bristol Bay Sat night/sun setting up southwesterly flow over 
the Mainland. Yet another wave develops over the NE Pacific sun and 
moves to the northern Gulf of Alaska Monday. 


Short term forecast... 


East...triple point center south of Kodiak this morning will 
continue east movement and weaken. Weak low which is forming south of 
the Kenai Peninsula is producing snow over the Gulf Coast and has enhanced 
the winds over the Prince William Sound and north Gulf. Snow should 
be tapering off at Kodiak through the night as tipple point moves 
east. Snow likely to continue along the north Gulf tonight with weak 
low holding over the northern Gulf. Some light overrunning snow will 
work inland in southcentral tonight with weak moisture push from the 
Gulf. Snow should taper off over southcentral Sat night...but next 
surge comes in early sun as frontal trough moves to the western Gulf. 
Easterly flow will increase over the Gulf Sun night/Monday as a strong 
low moves into the Gulf of Alaska. Majority precipitation with this 
system will likely remain initially along the coast with down-slope 
conditions inland. Warmer air will bring mixed precipitation with 
this system. 


West...a weakening frontal trough over Bristol Bay is producing some 
light snow over the area. Snow will diminish tonight as front 
continues to weaken and middle level flow shifts north. Storm force 
winds should slowly diminish over the western Aleutians as stacked 
storm force low in the western Bering Sea weakens and drifts south. 
Satellite imagery shows developing wave moving rapidly east toward 
the western Aleutians. Models pick up on this center as it 
intensifies and moves to western Bristol Bay Sun night. This center 
then becomes stationary and weakens through Monday. Associated front 
brings snow and blowing snow to the SW Alaska coast...especially 
Bristol Bay Sat night. 


Long term forecast...model differences and progressive pattern will 
cause timing issues. However...pattern is such that increased clouds 
and probability of precipitation with some warming are likely through the middle of next 
weak. 


Aer/alu...watch/warning summary 
public...none. 
Marine...gales 155,180,170,171,172,175,176, and 185. 
Fire weather...none. 


Rmc Nov 09 

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