Weather

353 
fxus65 kboi 071500 
afdboi 


Area forecast discussion 
National Weather Service Boise Idaho 
900 am MDT sun Sep 7 2008 


Discussion...12z boi radiosonde observation changed little from 12z Saturday from the 
surface to 850 mb but was 2c warmer than 12z Saturday from 850mb to 
700 mb. Therefore this afternoon will be at most 3f warmer. Winds 
aloft were west-northwesterly at 12z but will turn more northerly and increase later 
today which should limit warming further. Current forecast of 1-3f 
warmer than yesterday in downslope spots and 1-3f cooler in 
mountains should work out fine. Northwesterly surface winds will increase 
to 15-25 miles per hour in the snake basin. Winds will be 10 to 20 miles per hour in 
other exposed areas. Winds aloft will turn westerly Monday ahead of a 
short wave trough approaching from the northwest and surface temperatures will 
rise 2-4f. Surface cold front will arrive Tuesday morning starting 
a cooling trend. Note...previous short term wrote about Sunday in the 
last several lines...we have corrected it to say Monday. 


&& 


Aviation...widespread VFR under sunny skies today. Light surface 
winds with localized gusts to 25 kts. Light northwesterly winds 
aloft. 


&& 


Short term...today through Monday...northwest flow aloft will 
bring the a weak upper trough from southeast Washington at 3 am across SW Idaho 
5-8 am. Look for some clouds from Baker County through the west 
central/Boise Mountains with this wave. Deeper moisture 
instability and lift remain across Montana/Wyoming as the trough moves 
towards the southeast later today although NE mountains should again see 
some middle level cumulus clouds. Very dry air over western Oregon 
this morning is expected to filter across southeast Oregon and SW Idaho 
this afternoon. At the surface high pressure to the north and east and 
lower pressure to the S will keep a cool flow across the region. 
Some downslope spots could see 1-3 degrees of warming today but 
mountains will be 1-3 cooler and SW Idaho valleys will have highs 
similar to Saturday. An upper level jet axis is overhead across 
central Idaho again today will bring some gusty afternoon winds to 
25 miles per hour east of Boise. Dry conditions persist tonight with 
diurnal/terrain driven winds which may be slightly enhanced to 15 
miles per hour north of the Snake River/I.E. Jerome/ as NE to SW surface pressure 
gradient sets up. On Monday westerly flow and a building thermal 
axis...especially over southeast Oregon...bring around 2 degrees of 
warming to the valleys and 3-4 degrees to the mountains...2-5f 
above normal for early September. Light winds Monday. Westerly 
flow Monday could bring in some high cloudiness but it should be 
thin for sunny weather. 


Long term...Monday night through Saturday...early Fall like 
weather with the intermountain west between eastern Pacific Ridge 
and north central North America trough. Shortwave trough will 
approach the intermountain west early Tuesday for lowering heights 
and a breakdown of the upper level ridge. Shortwave will dig 
southeast across north Idaho Tuesday evening. 00z models much more 
progressive with upper trough than previous runs digging the 
trough across the forecast area Wednesday night. European model (ecmwf) and 
NAM/dgex have shifted their tracks further west as well but keep 
the majority of moisture east of the area. Will keep mostly dry 
forecast for now as this was the trend the last several model 
runs. More of an impact will be gusty west/northwest winds on 
Tuesday and Wednesday...as cyclonic middle-level flow and cold 
frontal passage will enhance diurnal surface winds. Temperatures 
will trend back to near normal Thursday through Saturday as trough 
tracks eastward and allows western Continental U.S. Ridge to regain strength. 


&& 


Aviation...VFR conditions under mostly clear skies with thin cirrus 
over Baker County Oregon and the west central and Boise Mountains 
today. Surface winds will be light with light to moderate northwest 
winds aloft. 


&& 


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


$$ 


Weather.Gov/Boise 


Discussion...lc 
aviation.....Mt 
previous short term...vm 
previous long term....js