Area Forecast Discussion
Issued by NWS Missoula, MT
FXUS65 KMSO 052136
Area Forecast Discussion
National Weather Service Missoula MT
236 PM MST FRI FEB 5 2016
.DISCUSSION...Another weather disturbance will be making its way
across the Northern Rockies later tonight through Saturday. As the
system approaches the region, the pressure gradient will tighten
creating gusty southerly winds on the Camas Prairie in Idaho.
Grangeville could have wind gusts up to 45 mph later tonight into
Saturday morning. Also this southerly wind will keep the
atmosphere well mixed during the overnight hours, so temperatures
for tonight should be relatively mild. Widespread precipitation is
expected as the cold front moves through the region. During the
onset of precipitation, snow levels will be fairly high causing a
wintry mix in many valley locations. After the passage of the
front by mid Saturday morning, snow levels drop to most valley
bottoms. Mountain passes, especially along the Montana/Idaho
border, will receive a significant amount of snow tonight through
Saturday evening. Winter weather advisories have been issued for
the travel impacts. The atmosphere becomes unstable enough for the
development of hefty snow showers. The atmosphere profile
indicates that snow bands will be possible by Saturday afternoon
and lasting into the evening hours. Snow bands will be able to
produce very heavy snow in a very short distance which will be a
major impact on area roadways. At this time, it is difficult to
pin point where and when snow bands will develop on Saturday.
A strong ridge of high pressure will build over the West Coast
extending into the Northern Rockies resulting in dry conditions
Sunday through much of next week. As is typical with these strong
winter ridge patterns, valley inversions will develop with the
potential for low stratus, fog, and decreasing air quality.
Seasonably cold temperatures are expected for valleys under the
inversions, while higher elevation valleys and the adjacent
mountains experience well above normal temperatures and frequent
By late next week, forecast models bring a cold front through and
begin to breakdown the ridge but confidence is low on the timing
and strength of the cold front. Most likely this will not be a
significant event with much of the energy absorbed by the ridge.
.AVIATION...A transitory ridge of high pressure has create fair
flying conditions this afternoon and evening. The conditions will
steadily deteriorate tonight as another system will make its way
across the Northern Rockies. Ceilings will be steadily dropping
tonight and widespread snow showers are expected by the morning.
These showers will be capable of producing heavy snow, so
visibilities could be reduced to less than a mile at times. Snow
bands are a possibility by Saturday afternoon, creating another
issued when the band is within the vicinity of the terminal.
.AIR STAGNATION...Confidence remains high that a strong ridge of high
pressure will build across the region late Sunday and last through
late next week, allowing valley inversions to develop and persist.
Stable conditions will lead to decreasing air quality especially
for the lower valleys of western Montana and Lemhi County in
Idaho. The next potential break up of the stagnate conditions will
be Friday or Saturday of next week as the ridge of high pressure
gradually breaks down.
MT...Winter Weather Advisory from 11 PM this evening to 11 PM MST
Saturday ABOVE 4000 FEET for the Bitterroot/Sapphire
Mountains...Lower Clark Fork Region...Potomac/Seeley Lake
Region...West Glacier Region.
ID...Winter Weather Advisory from 10 PM this evening to 10 PM PST
Saturday ABOVE 4000 FEET for the Northern Clearwater
Mountains...Southern Clearwater Mountains.