293 
fxus65 kboi 091017 
afdboi 


Area forecast discussion 
National Weather Service Boise Idaho 
317 am MST Friday Jan 9 2009 


Short term...today through Saturday...as heights rise and an 
upper level ridge begins to build into the Pacific northwest...we will see 
drier weather into the weekend. Cold air will be felt for a couple 
days before the warming associated with the upper level ridge 
arrives. We will be looking at highs 10 to 15 degrees cooler than 
in recent days for today and Saturday. Similarly...overnight lows 
Friday night will be 10 to 20 degrees cooler than those from 
Thursday morning. We will see only a slight chance of showers in 
the far NE corner of our County Warning Area...in the west central mountains... 
today. This chance will diminish tonight...and Saturday looks dry 
for all of southeast Oregon and SW Idaho. The beginnings of a Treasure 
valley inversion may start as early as Saturday. With light 
winds Saturday morning...left fog in the forecast per previous 
package. 


Long term...Saturday night through Thursday...upper level ridge 
remains the dominant feature as it builds east into the region. 
Moist northwesterly flow...aided by upper level jet...will remain 
over the NE corner of the forecast area for the first part of the 
extended for clouds and a slight chance for showers over the 
northern mountain zones. GFS model keeps the forecast area in this 
northwesterly flow through at least Wednesday...before the ridge 
axis gradually shifts onshore. Based on the new model runs... 
inversion seems more and more likely though the question is...will 
there be enough moisture in the boundary layer for fog/stratus. 
Uncertainty in how much moisture will still be present across the 
region after several days of dry weather and whether the lowest 
layers of the atmosphere will be able to cool enough for 
saturation to occur...will continue to keep fog out of the 
forecast. No major changes to previous forecast. 


&& 


Aviation...VFR conditions today. Surface high pressure building in 
from the west will provide light southwest to northwest surface 
winds. Light or calm winds and mostly clear skies will allow patchy 
valley fog to form in the mountain valleys by 12z locally lowering 
ceilings and visibilities to IFR/LIFR. Fog should dissipate by about 
19z. Otherwise expect VFR conditions Friday except for local 
mountain obscuration in low clouds. Winds aloft will be light to 
moderate northwest. 


&& 


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


$$ 


Weather.Gov/Boise 


Short term...snow pellets 
long term....js 
aviation.....Js