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Area forecast discussion 
southcentral and southwest Alaska 
200 PM akdt Friday Jul 18 2008 


Analysis and upper levels...major upper level closed low that has 
brought rain to much of the state the past couple days is slowly 
transitioning eastward from southwest Alaska to southcentral Alaska. 
There are multiple upper level centers and vorticity maximums 
embedded within the larger cyclonic circulation...resulting in slow 
and variable movement of showers across Mainland Alaska. There are 
also two weak surface centers...the original parent low off the 
Kuskokwim Delta coast as well as a remnant triple point low east 
of Seward. These lows are both dissipating. Radar imagery shows 
shower activity diminishing across the southern Mainland. Much of 
southcentral received over one inch of rain. The combination of 
rain and snowmelt has resulted in high running rivers and streams 
in the western Susitna Valley. A Flood Warning has been issued for 
the yentna river at Long Creek and surrounding tributaries. Water 
levels have nearly reached bankfull in this area and will continue 
to crest through tonight or Saturday morning...resulting in minor 
flooding. 


The upper jet is nearly zonal...running along the Aleutians and 
across the southern Gulf to Southeast Alaska. A weak surface low 
south of the western Aleutians is being driven quickly 
eastward...just brining some rain to the Aleutians. 


Model discussion...models initialized reasonably well and are 
in good agreement through the weekend. Solutions have come into 
agreement with the Arctic front dropping down into western Alaska 
Sunday night and Monday. There has been a trend toward a slower 
solution...which the European model (ecmwf) has been indicating...so this will be 
adopted into the forecast. The details become questionable heading 
through the beginning of next week due to complexities inherent in 
closed upper level lows...but large scale implications are handled 
well by the current forecast. 


Short term forecast...the upper level low complex will move 
overhead of southcentral Saturday and then continue eastward into 
Canada Sunday into Monday. Showers will gradually end across 
southwest Alaska tonight and diminish a bit over southcentral 
Saturday. Showers will generally be slow moving...so rainfall 
amounts will be quite variable. There will be little or no break 
before another upper level closed low drops down out of the 
Arctic...pushing an Arctic front across southwest Alaska Sunday and 
into southcentral Monday. Southwest Alaska may see a little sun 
Saturday...but southcentral will remain mostly cloudy with a few 
showers until the impacts of the next system are felt Sunday night. 
Similar to the system from the past couple days...significant 
rainfall can be expected once again. Will have to keep an eye on the 
flooding potential since some rivers and streams are now running 
high. 


High pressure will build over the Aleutians Saturday as a weak 
surface low tracks away from the area. This will hold until early 
next week as a low approaches the western Aleutians. 


Long term forecast...a mean trough will remain over Mainland Alaska 
through next week...so cool and wet weather will persist. 


Aer/alu...watch/warning summary 
public...ashfall advisory zone 185. 
Flood Warning zone 145 for yentna river at Lake Creek. 
Marine...ashfall advisory zone 170. 
Fire weather...none. 


Seb Jul 08 

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