471 
fxus65 kboi 221006 
afdboi 


Area forecast discussion 
National Weather Service Boise Idaho 
306 am MST Sat Nov 22 2008 


Short term...today through Sunday...weak upper trough and cold 
frontal passage today followed by brief stagnant period starting 
Sunday. Surface analysis at 09z places the cold front just east of 
Portland and west of Medford. This matches up pretty well with 
model depiction of the surface front thus the timing of frontal 
passage in Boise around 19z looks good. Main vorticity maximum is well 
north of the area...southwestern Canada...with another vorticity maximum 
expected to move a little further south...NE Oregon into north 
central Idaho...later today. In terms of precipitation with the 
front...latest model guidance continues to trend drier. Radar 
imagery over western Oregon this morning confirms this as the 
coverage of showers and precipitation amounts ahead of the front are 
quite a bit less than model forecasts. These showers are moving 
northeast ahead of the front and are mainly confined to northern 
Oregon and western Washington state. There have been a few shower 
in southwestern Oregon...however they are having a tough time 
sustaining themselves as they move east into the dry air over southeast 
Oregon. Based on this...have lower probability of precipitation across area today. At 
present...think the best change for precipitation will be across 
Baker County into the west central later today with second vorticity 
maximum. But dry air and limited upper level support will keep precipitation 
chances near 30 percent in the areas listed above. Deep upper 
level trough moving into the Gulf of Alaska today will allow the 
upper ridge to rebuild into the region tonight bringing a brief 
return to stagnant conditions starting Sunday. Inversions 
strengthen Sunday afternoon which will trap cooler air in the 
lower valleys. 


Long term...Sunday night through Saturday...a new ridge builds over 
the area Sunday through Tuesday with quite a bit of amplitude. This 
is in response to a deep storm system taking shape over the Great 
Lakes and northeast. Overall pattern across Continental U.S. Becomes blocky 
with operational models indicating a series of closed lows across 
the country. Thus...systems will tend to stay in place longer as is 
common in a blocked pattern. For our region...a closed low will 
linger in the Great Basin about the Wednesday and Thursday time 
frame in a split 500 mb pattern across the western United States. 
Confidence in precipitation and general storminess remains rather 
low over the all important Thanksgiving Holiday travel period. Have 
trended probability of precipitation down with adjacent offices to start the period as the 
effects of the ridge are still in place. Then trended toward climatology 
probability of precipitation near the Holiday itself and the days just following as the 
split and closed low continue to dominate the region. Seasonal 
temperatures are anticipated in this pattern with no outbreaks of 
cold air and nothing very mild either. 


&& 


Aviation...weak upper front crossing eastern terminals at 1000z 
with broken to overcast high clouds. A several hour window of clear skies 
through middle morning before another weak front moves east across 
eastern Oregon this afternoon and Idaho this evening. Expect VFR 
conditions to prevail with unrestricted visibility today. This 
evening...MVFR conditions to develop over kmyl...kbke and kbno with 
partial mountain obscuration in lowering ceilings and scattered snow 
showers. Moderate west winds aloft decreasing tonight and Sunday. 
Light to moderate east surface winds. 


&& 


Boi watches/warnings/advisories... 
Idaho...none. 
Or...none. 
&& 


$$ 


Weather.Gov/Boise 


Short term...jds 
long term....gs 
aviation.....Gs