Weather

356 
fxus65 kboi 052219 
afdboi 


Area forecast discussion 
National Weather Service Boise Idaho 
320 PM MST Monday Jan 5 2009 


Short term...current storm is winding down over the forecast area 
but lingering bands of snow showers remain in northwest flow aloft. 
Will cancel all current warnings and advisories early at 3pm with 
the exception of southern Twin Falls County and the western Magic 
Valley where storm effects will linger for awhile longer this 
evening in upslope flow. Attention now gets directed back upstream 
as a new system takes aim on the area. This new weather system is 
only about 12 hours behind the current one...so we will only see a 
brief period of less active weather this evening. This next storm 
has a deeper and longer lasting plume of moisture associated with 
it...but temperatures and snow levels will begin rising along a warm 
front and then pushing northward into the mountains by Tuesday 
afternoon. Thus...snowfall amounts will be limited and below warning 
criteria and spread out over a longer period of time. Have therefore 
decided to issue a Winter Weather Advisory for this next system with 
rather seamless amounts of snow occurring over this area in a longer 
period of time. A rain snow mix is expected in the Snake River 
Valley tonight but quickly should go over to all rain on Tuesday as 
warmer air works north along a warm front. Temperatures rise into 
the low 40s Tuesday afternoon and middle 40s by Wednesday in the 
southern part of the forecast area as a large intense ridge aloft 
builds off the central California coast sending milder air 
northward. 


&& 


Long term...Wednesday night through Monday...upper ridge building 
over the eastern Pacific will keep moist northwest flow over the 
northwest. Shower activity lingers mainly across the west central 
and Boise Mountains into Wednesday night with snow levels around 
6500 feet mean sea level. Another shortwave trough and weak cold front will move 
through southeast Oregon and SW Idaho on Thursday bringing precipitation and 
dropping snow levels to around 4500 feet. Snow amounts will be tricky 
as snow levels ahead of the front will be above 6000 feet before 
dropping quickly with the frontal passage. Have forecast snow totals 
above 6500 feet for Thursday in the west central and Boise Mountains 
of 8 to 12 inches with the mountain valleys seeing 4 to 8 inches. 
The lower valleys will see just rain as snow levels remain above the 
valley floors. Headlines could be need for the mountains on 
Thursday. Good model agreement in placement and amplification of the 
ridge which will shift into the west for the weekend bringing drier 
conditions. Temperature inversion is certainly possible for the 
weekend...though this will depend on far east the ridge builds. 
Models Keep Ridge axis off the West Coast which will keep moist 
northwest flow bringing weak shortwaves in to the region. Will keep 
temperatures towards ensemble guidance which keeps lows near normal 
and highs about 5 degrees above normal. 


&& 


Aviation...snow tapering off across southeast Oregon and SW Idaho this 
afternoon for improving conditions. MVFR-LIFR conditions and 
mountain obscuration continue across SW Idaho this afternoon ending 
around 00z except the west central and Boise Mountains. Do not 
expect temperatures to warm enough for snow to switch to rain this 
afternoon except in Harney and Malheur counties. Southeast-SW surface winds 
will be gusty throughout the area with gusts up to 30 kts...making 
for areas of blowing and drifting snow. Northwest winds aloft will be 
strong. Another upper trough moves into the region early Tuesday for 
widespread MVFR conditions in rain across the Lower Valley of southeast 
Oregon and SW Idaho and snow above 5500 feet. 


&& 


Boi watches/warnings/advisories... 
Idaho...Winter Weather Advisory until 8 PM MST this evening for 
idz016-idz030. 
Winter Weather Advisory from early Tuesday through Tuesday 
night for idz011-idz013. 
Or...Winter Weather Advisory from early Tuesday through Tuesday 
night for orz062. 




$$ 


Weather.Gov/Boise 


Short term...gs 
long term....js/ja 
aviation.....Js