059 
fxus65 kmso 211042 
afdmso 


Area forecast discussion 
National Weather Service Missoula Montana 
342 am MST Sat Nov 21 2009 


Discussion...a vigorous cold front has crossed much of the northern 
rockies early this morning and will be east of the Continental 
Divide by sunrise. This feature has produced a couple to several 
inches of snow mainly across north central Idaho as indicated by 
snotel sensors and Highway cameras at Lolo and lost trail passes. 
Strong winds...particularly in the mountains have also resulted 
from the frontal passages. The air mass behind the front and under 
a passing upper level trough will be very unstable and moist 
through midday. Therefore...all areas will see snow showers 
develop. North central Idaho will continue to see the best 
accumulations...and thus the Winter Weather Advisory will be 
continued through late morning. Blowing snow may cause areas of 
poor visibility in the mountains as winds are expected to stay 
breezy. 


A second system will barrel into the northern rockies Sunday. This 
will also be a good snow producer similar to the current trough. 
And again north central Idaho will see the greatest 
accumulations and have issued a second Winter Weather Advisory for 
that area Sunday through Sunday evening. The bitterroots will also 
see several inches of snow with this event from Lookout Pass area 
south to Lost Trail Pass...so have included this area in the 
advisory. This system will also have increased winds with some 
blowing snow possible. 


Light accumulation in the valleys are possible both today and with 
sunday's system as snow levels have lowered to all but the lowest 
valleys in north central Idaho. 


Monday through the week...the northern rockies will enter into a 
ridging pattern through the bulk of next week. The first hints of a 
ridge of high pressure will form throughout the day Monday...but 
may be interrupted by a shortwave passing to the north in Canada. 
While this wave doesnt look to move far enough south to have any 
true affects on the region...flow will remain unstable 
enough in northwest Montana for showery precipitation to 
occur but remain confined mostly to higher elevations. High 
pressure will then have a better chance to rebuild over the 
northern rockies Tuesday night and will continue to strengthen 
through the end of the week. 


&& 


Aviation...snow showers will develop under an unstable upper 
trough through the morning causing intermittent visibility and 
ceiling reductions at all terminals. The showers will decrease 
somewhat in coverage by late afternoon but likely continue over 
the mountains into the early evening. 


&& 


Mso watches/warnings/advisories... 
Montana...Winter Weather Advisory from 5 am to 11 PM MST Sunday for 
Lower Clark Fork region. 


Winter Weather Advisory from 5 am to 11 PM MST Sunday for 
Bitterroot/Sapphire Mountains. 


Idaho...Winter Weather Advisory until 10 am PST this morning for 
northern Clearwater Mountains-southern Clearwater Mountains. 


Winter Weather Advisory from 4 am to 10 PM PST Sunday for 
northern Clearwater Mountains-southern Clearwater Mountains. 


&& 


$$ 


Short term...Whitmore 
long term....allegretto 
aviation...Whitmore