346 
fxak68 pafc 071259 
afdafc 


Area forecast discussion 
southcentral and southwest Alaska 
500 am akdt Tuesday Oct 7 2008 


Model discussion... 
in the short term the models are in good agreement again. NAM 
continues to be better at resolving the individual shortwaves moving 
through the region although the GFS is just fine with the synoptic 
level features. For that reason the NAM was used for the 24 hour 
forecast. After about 48 hours there are still some differences in 
the models on the low moving into the central Aleutians. This 
mornings GFS solution differs from yesterdays 00z solution but shows 
good consistency with the 12z and 18z runs. The new solution shows 
the low moving into the central Aleutians and then retrograding 
slightly before moving eastward toward the Mainland. Yesterdays 12z 
European model (ecmwf) did not agree with this solution and pushed the low up the West 
Coast more quickly...however the New Run has trended toward the GFS. 
Given this trend and the GFS consistency it was chosen for the Middle 
Range and extended forecast. Also of note is the fact that the GFS 
is a much stronger solution than the other three models. With the 
upper level support this solution does not seem unlikely and the GFS 
has been consistent on the strength for several days so the forecast 
went with this solution although it seems to be an outlier. 


Analysis and upper levels... 
the upper level trough is beginning its shift eastward today but this 
morning still lingers over the central Mainland. At the surface a 
low has moved into Prince William Sound and is bringing a strong band 
of moisture into the eastern zones. As this low moves eastward the 
cold air will advect in behind it and enhance the snowshowers. With 
the eastward shift of the pattern the upper level ridge will move 
over the Mainland and a stronger upper level low will move over the 
Aleutians...providing upper level support for a new surface low 
forecast to move into the Aleutians on Wednesday afternoon. This 
will cause the surface low to retrograde westward and 
strengthen...becoming the first significant storm of the season. 


Short term forecast... 
east of the Alaska Range...a strong shortwave that turned into a 
closed surface low has moved into Prince William Sound and brought 
much of the southcentral area the first snow of the season this 
morning. As the surface low lingers in Prince William Sound periods 
of snow will continue for the southcentral region today. Temperatures are 
still pretty warm...both on the ground and aloft...so the snow will 
be pretty heavy and will compact and melt reducing the accumulation. 
Not much moisture from this shortwave is expected to make it across 
the chugach range and into the Copper River basin but the area could 
see some showers. As the low moves eastward tomorrow the snow will 
taper off and there will be a brief respite before the low in the 
Aleutians begins to affect the eastern domain. Gale Warning winds 
will begin to show up in the marines on Thursday and strong winds are 
expected for Turnagain Arm Thursday night as the region experiences 
its first Chinook event of the season. 


West of the Alaska Range...calm weather for the western zones today 
will not last long as that next big low moves up tomorrow afternoon. 
In the meantime winds will decrease and showers will diminish as the 
shortwave ridge moves overhead. Once the low moves into the central 
Aleutians the effects depend highly on its track. As the warm front 
moves through the eastern Aleutians and western Alaska Peninsula and into the 
eastern Bering gale force winds can be expected in most of the 
marines with strong wind headlines for the pribilofs...Unalaska...and 
the western Alaska Peninsula. These winds will move off onto the Mainland as 
the low starts to shift eastward beginning Thursday. 


Long term forecast... 
the strong low in the Aleutians is forecast to move up the Aleutians 
and onto the West Coast near King Salmon on Friday night. The cold 
air advection behind this system is strong and may bring storm force 
winds to the Aleutians at the end of the week. Meanwhile the 
Mainland can expect to see a Big Warm up...with a melt of all the 
snow and a significant Chinook event for the east in particular. 




Aer/alu...watch/warning summary 
public... 
marine... 
fire weather... 


*** Oct 08 

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