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fxus65 kpih 212052 
afdpih 


Area forecast discussion 
National Weather Service Pocatello Idaho 
200 PM MST Sat Nov 21 2009 


Short term...tonight through Tuesday. A dirty(moist) short-wave 
ridge will spread quickly across the region tonight ahead of the 
next Pacific storm system which was clearly visible on water vapor 
satellite imagery off the northwest coast. This system will spread into 
Washington and Oregon overnight then through Idaho Sunday with 
lingering precipitation activity across the eastern Highlands through 
Sunday evening. A strong upper jet (140kts) will accompany the wave 
through the region with 700mb (10k ft) winds ramping up to 45kts. 
Low level lapse rates are unstable enough to mix down a good portion 
of these winds to the surface as gusts and for now we have sustained 
winds and gusts running up close to advisory levels. The statistical 
guidance is downplaying the strength of the winds however so will 
hold off on that particular highlight for now. As for the storm 
total snowfall...we have enough wind and snow in the central mountains 
to warrant a warning for Sunday with lesser...advisory amounts for 
the remainder of the central and eastern Highlands through Sunday night. 
After midnight Sunday...a ridge of high pressure will begin to build 
across the region providing drier but cool conditions. Huston 


Long term...Tuesday night through Saturday...with storm exiting to 
east...high pressure ridge will start to develop. Model consensus 
favors a higher amplitude ridge and drying conditions through 
Thursday. Current forecast reflects much lower probability of precipitation and less clouds 
during that time period. A slight warming trend expected with ridge 
development. Starting Friday models show some differences. Both 
the European and GFS models push a shortwave trough through the the 
northwestern tier of states. However the European is much deeper 
than the GFS. Modelers are trending toward a compromise...which 
means we will get a brushing from the system...but most energy to 
remain to the north of US. Current gridded forecasts have this 
uncertainty reflected. Preston 
&& 


Aviation...Post frontal clouds continue to linger in eastern 
portions of the area with MVFR conditions possible for pih and Ida 
until 00z. Biggest concern remains the gusty winds which will begin 
to diminish with sunset. Next weather system to impact area 
starting tomorrow morning and expect lowering clouds by sunrise and 
precipitation...mainly snow to develop between 15 and 19z as frontal 
boundary and another shot of gusty winds moves through. Periods of 
light to moderate snow producing MVFR to IFR conditions expected 
through early evening. Preston 
&& 


Pih watches/warnings/advisories... 
Winter Storm Warning for The Sawtooth mountains and Wood River 
region for Sunday. 


Winter Weather Advisory for the Lost River/pahsimeroi region for 
Sunday. 


Winter Weather Advisory for the eastern mountains Sunday afternoon 
through Sunday night. 
&& 


$$