693 
fxus65 kboi 202215 
afdboi 


Area forecast discussion 
National Weather Service Boise Idaho 
315 PM MST Friday Nov 20 2009 


Short term...tonight through Sunday...pre-frontal gusty east to 
south winds have been locally very windy in the Mountain Home area 
and parts of southern Harney County today. Local blowing dust was 
observed as well. Winds are expected to decrease to 15-30 miles per hour 
through the late afternoon then shift to the SW and northwest 15-35 miles per hour 
with the cold frontal passage. The front appeared to have crossed 
into the Lee of the Cascades in west central Oregon as of 2 PM and 
should reach the Oregon-Ida border 5-6 PM MST. Precipitation looks to lag 
the front by 2-3 hours for a quick shot of rain and snow this 
evening in Oregon and precipitation changing to snow above 3000 feet in 
Idaho tonight. Valleys look to dry out Saturday morning as snow 
showers linger in the Baker mountains until noon and Idaho 
mountains through mid-afternoon. Cold and dry but considerable 
cloudiness around Saturday night along with another round of gusty 
southeast to south winds. Near normal temperatures for lows 
tonight through highs Sunday after warming up into the 40s and 50s 
this afternoon. 


A stronger and colder system into southeast Oregon late Saturday night 
and across Idaho Sunday looks to be a potential winter storm. Warm 
advection and moisture with around 120 percent of normal precipitable waters  
quickly transitions to cold unstable conditions with widespread snow 
showers through the afternoon in the mountains. Up to a foot of 
new snow is possible Sunday in the west central and Boise 
Mountains along with areas of blowing and drifting snow. Last two 
runs of the NAM have shown 8-16 inch snow accumulations Sunday 
but the GFS is closer to 8-10 maximum amounts and the ec 4-7 inches 
based on quantitative precipitation forecast...so there is still some uncertainty in the 
qpf/snowamt. The storm tracks are similar so a weather story has been 
issued to highlight the possibility of a winter storm Sunday 
across the northern mountains. Snow levels will be at valley 
floors in the morning and an inch or so is expected at Boise early 
Sunday morning. 


Long term...Sunday night through Friday...snow showers will linger 
across the central Idaho mountains and western Magic Valley Sunday night 
before drying out on Monday. This will transition toward a period of 
high pressure as an upper level ridge will build over Oregon Tuesday 
through Thursday. The ridge will amplify over the forecast area on 
Wednesday and Thursday for predominantly dry conditions /and minimal 
afternoon mixing/ through early Friday. This could bring an 
inversion to the low elevation valleys over the Holiday travel 
period for air quality and visibility impacts. Have adjusted the 
forecast grids to reflect inverted temperatures based on elevation 
..along with weak southeast winds through Thursday night. Models are 
in reasonable agreement bringing the next Pacific trough into the 
area late Friday or Saturday. 


&& 


Aviation...moderate southeast to SW surface winds /local gusts to 40 kts/ 
through tonight with advancing cold front. Winds aloft will be 
moderate to strong southwesterly. Rain and snow showers will develop 
along a line from kbke to kbno through 00z and will move east through 
the night with diminishing ceilings and deteriorating conditions. Expect 
areas of MVFR and local IFR across southeast Oregon the remainder of the 
afternoon...after 03z for Idaho. Snow levels approximately 3500 feet 
..with rain and snow mix across lower valleys. 


&& 


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


$$ 


Weather.Gov/Boise 


Short term...vm 
long term....cd/LH 
aviation.....Cd