377 
fxus65 kmso 210340 
afdmso 


Area forecast discussion 
National Weather Service Missoula Montana 
940 PM MDT Sat Mar 20 2010 


Update...adjusted minimum temperatures in many valleys of the 
intermountain region tonight. 




&& 


Discussion...despite the ample warming the intermountain west saw 
today...temperatures are falling rather quickly this evening with 
dry air at the lower levels. Adjusted minimum temperatures closer 
to Saturday mornings readings...but a few degrees warmer. 
Remainder of forecast is on track. 




&& 


Aviation...ridge of high pressure will keep skies mostly clear 
and surface winds light through 21/1800z. An approaching Pacific 
system and associated cold front will increase middle level clouds 
and surface winds...with some stronger gusts...before spreading 
thicker clouds and precipitation west to east across the northern 
rockies. Ceilings and visibilities may be impacted at all area 
airfields late Sunday afternoon...after 22/0000z. 


&& 


Previous discussion... /issued 258 PM MDT Sat Mar 20 2010/ 


Discussion... 


Tonight through Monday night...high pressure will be the dominant 
weather feature present through early Sunday...with mostly clear 
skies and light breezes present. By early Sunday afternoon...clouds 
and wind will increase ahead of a Pacific storm system. Unlike the 
systems that have affect north central Idaho and western Montana 
during this recent winter...the Pacific jet stream will play a 
significant role. The jet will be important for moisture transport 
and precipitation potential across the region. However...timing of 
these significant features will be one source of uncertainty for 
Sunday afternoon through Sunday evening. Much of the available 
guidance depicts the northern rockies as dry through late Sunday 
afternoon...however the Pacific jet stream arrives during late 
Sunday afternoon. The arrival of the jet stream overhead will signal 
the beginning of precipitation. Initially...high elevations and 
mountain passes will receive snow...while lower elevations 
experience rain. By early Monday...snow levels will drop enough for 
higher elevation valleys to receive some snow. As the storm system 
moves from northwest to southeast across the region between Sunday 
and Monday evening...precipitation potential will follow suit. 
Colder temperatures are anticipated in the wake of this 
system...however given how late in the cool season that it is...most 
population centers will not receive measurable snowfall. Mountain 
passes may be a concern...with current forecast snow amounts ranging 
from 4 inches at Lolo Pass to 8 inches at Lookout Pass for the 
period Sunday evening through Monday evening. As of now...winter 
weather highlights will be put on hold. 


Tuesday...the trough moves off to the southeast during the day...the 
atmosphere near the Continental Divide will be unstable 
enough for lingering showers. 


Tuesday night through Thursday morning...a ridge builds in from the 
west...bringing a warming trend. 


Thursday through Friday...medium range models do have some timing 
differences with the GFS about 6-12 hours faster (than the other 
models) with the next Pacific system as well as the onset of 
precipitation. Consensus would have Thursday as a good chance of 
precipitation...with conditions remaining unsettled into Friday. 






&& 


Mso watches/warnings/advisories... 
Montana...none. 
Idaho...none. 
&& 


$$ 


Update...Mead 
previous discussion....zumpfe/kolata 
aviation...Nolte