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Area forecast discussion 
southcentral and southwest Alaska 
130 PM akdt Tuesday Aug 19 2008 


Analysis and upper levels... 
large vertically stacked low is moving east-southeast into Juneau aor this 
afternoon. Inverted trough extends northwest from the center of the 
low across southwest Alaska toward the Kuskokwim Delta. High pressure 
remains in control over the central and eastern Bering Sea...bringing 
widespread low clouds and fog to the area. Another weak vertically 
stacked low is developing 200 nm west of Attu Island. 


Model discussion... 
all models in agreement on major features in the short term. Some 
inconsistencies from run to run in the medium and long range has lead 
US to blend in the latest GFS with the inherited European model (ecmwf) based 
forecast. This solution resulted in a nice transition of the mean 
upper low from the Bering to the northern Gulf late in the week. We 
anticipate the models will continue to have a hard time with this 
transition. Thank you Juneau and HPC for the coordination. 


Short term forecast... 
southcentral...winds are quickly dying down over the western Gulf as 
the large low pulls away from our area of responsibility. A few gale 
warnings are still posted for this afternoon but will be lifted with 
the new forecast package in a couple of hours. A large deformation 
zone will remain over southcentral Alaska associated with a inverted 
trough extending across the Alaska Range. The weak cyclonic 
circulation will result in an increasing chance of showers each day 
through the end of the week. Near or just below climatological normal 
temperatures will persist with partly to mostly cloudy skies. 


Southwest Alaska...our attention is focused this afternoon on the 
lower Kuskokwim River and the northern Bristol Bay public forecast 
zone where the threat of thunderstorms exists. A shower already 
produced a lightning strike this morning north of Stuyahok associated 
with the vorticity maximum in the area. Bethels morning sounding looking 
relatively unstable although a cumulus field has yet to develop this 
afternoon...a result of the large cirrus shield and stubborn morning 
fog. Will wait to see the 00z Bethel sounding to decide whether or 
not to drop the thunderstorm wording from the forecast but at this 
point...still expecting some type of activity to develop in the next 
3 hours. 


More stable air has filtered in over the upper Kuskokwim valley 
today. The broad area of low pressure mentioned in the southcentral 
section will likely spill over the Alaska Range and provide the 
Kuskokwim with similar weather during the week...partly to mostly 
cloudy skies with scattered rain showers in the afternoon. Today 
looks to be the best potential for thunderstorms. 


Bering Sea and Aleutians...okmok Volcano increased activity lead to 
another ashfall advisory for Umnak Island through noon Wednesday. 
Light synoptic winds will confine any light ash that is emitted to 
the vicinity of the island. Unalaska Island is not being impacted at 
this point. 


Widespread fog and low clouds persists over the central and eastern 
Bering Sea under the weak surface high pressure in the area. This 
area of high pressure will slowly weaken during the week but not move 
much. A weak low to the west of Attu Island will drift east toward 
the western Bering Sea and eventually result in a broad area of upper 
low pressure over the central and eastern Bering. A couple of 
impulses embedded within this broad trough will result in occasional 
showers. 


Aer/alu...watch/warning summary 
public...ashfall advisory 185. 
Marine...none. 
Fire weather...none. 


Ab Aug 08 

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