638 
fxus65 kboi 211600 
afdboi 


Area forecast discussion 
National Weather Service Boise Idaho 
1000 am MDT Thursday Aug 21 2008 


Discussion...minor updates were made to the forecast for today 
as rain showers in northern Baker County extending eastward into 
Adams and valley counties were diminishing and moving 
northeastward. These areas should be the only ones to receive rain 
today...so we removed the mention of rain showers elsewhere. The 
rest of the forecast for a cool...breezy day is still on track. At 
9:45 am gusty winds were already beginning to occur over portions 
of eastern Oregon. These breezy conditions will spread into Idaho 
this afternoon with wind gusts up to 30 miles per hour in the Snake River 
Plain and along ridge tops. 


&& 


Aviation...isolated MVFR conditions in rain showers through 
00z...mainly across Baker County Oregon and the west central 
mountains of Idaho. Mountains will be obscured. Moderate surface 
winds with gusts to 35 kts through 03z. Moderate to strong 
westerly winds aloft. 




&& 


Previous discussion... 
short term...today through Friday...brunt of the shower activity 
the past several hours has been located just to the north of the 
County Warning Area...with Baker County stations reporting light rainfall amounts at 
times...less than a tenth of an inch. This area was situated in a 
more favorable precipitation regime aided by a 120 knot upper jet 
associated with the oncoming Pacific low. Model trends continue to 
support the idea that basically the same areas will receive the bulk 
of the rainfall today...so will keep likely probability of precipitation across the extreme 
north portion this morning...with little to no threat of rain south 
of Burns and Idaho City. Scattered showers will continue this 
afternoon in essentially the same aforementioned areas but will end 
this evening as the upper low moves rapidly east. Breezy west to 
northwest winds of 15 to 25 miles per hour with higher gusts will be the rule 
by midday. Afternoon highs will run about 4 to 8 degrees cooler 
today as compared to Wednesday...with middle 60s to middle 70s in the 
mountains and middle 70s to middle 80s in the valleys. For tonight through 
Friday...upper low continues to track well east as a much drier 
airmass in association with a weak high pressure ridge builds into 
the area. Winds will gradually diminish overnight as surface high 
pressure settles into the Idaho Panhandle. Skies will clear as 
well...and the combined effects of the clear skies and light winds 
could result in patchy fog in the Long Valley. Temperatures will 
start to recover on Friday as the ridge starts to build. 


Long term...Friday night through Wednesday...return to positive pna 
pattern this weekend as upper ridge builds across the intermountain 
west. Model in good agreement with relatively low amplitude ridge 
building across the intermountain west/Rocky Mountain region 
starting Saturday. Ridge remains somewhat suppressed as energy from 
another upper level trough moves across southern Canada. 
However...temperatures should rebound back above normal Saturday 
through Tuesday. Warmest day looks to be Sunday as surface thermal 
trough over the area and 850-700mb thickness could support near 100 
degree temperatures. However...models are also showing increased cloud 
cover/possible convection with moisture moving in from the central 
Pacific which could limit warming. Plus breezy west-southwest winds 
ahead of approaching upper low from western Canada could keep 
temperatures cooler as well. Timing and amplitude of the next trough 
remain uncertain but is shown to arrive Tuesday or Wednesday. GFS 
much more progressive with the low which looks very similar to 
yesterdays/todays current low except for a more southerly track. 
European model (ecmwf) has a much weaker open trough which remains further north of 
the County Warning Area. Due to the uncertainty have continued forecast toward 
climatology for those days. 


&& 


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


$$ 


Weather.Gov/Boise 


Discussion...jb 
aviation.....Mt 
previous short term...bw 
previous long term....js