585 
FXUS65 KMSO 112132
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
232 PM MST Mon Feb 11 2019

...PROLONGED SNOW WITH PERIODS OF MODERATE SNOW THROUGH THE MIDDLE
OF THE WEEK...

.DISCUSSION...The brief break in snow this afternoon will be
short-lived as a warm front quickly brings a return to snow 
during this evening. 

A period of overrunning (warm frontal boundary moving over a cold
air mass near the surface) will produce moderate to heavy snow 
tonight into Wednesday across portions of north central Idaho and 
northwest Montana. Snow will initially impact north central Idaho 
and western Montana tonight before spreading across northwest 
Montana by early Tuesday morning. Winter Storm Warnings have been 
issued for parts of north-central Idaho and northwest Montana as 
intense period of snowfall is expected as the warm frontal 
boundary is lifted over the cold air stuck near the surface. 
Snowfall rates on the order of one to two inches per hour will be 
common along this warm frontal boundary as it lifts northward into
northwest Montana Tuesday morning. 6 to 10 inches of snowfall is 
anticipated across these areas, with over a foot of snow in the 
higher terrain near the Idaho/Montana border. Further south and 
east, across west central Montana, snowfall will generally be the 
1 to 4 inch range.

A surface low will track across central Oregon into northeast 
Washington tonight and will act to increase a southerly pressure 
gradient across north central Idaho. This will bring an increasing
trend to winds through the Camas Prairie in Idaho and southwest
Montana through Tuesday afternoon. The wind combined with 
snowfall will make for a period of lowered visibility due to 
blowing snow across the Camas Prairie, particularly near the 
Grangeville area. 

Warm and moist air will continue to stream across much of the 
Northern Rockies Wednesday. The greatest impacts will be felt 
across the I-90 corridor west of Missoula through Lookout Pass and
for Highway 2 from Columbia Falls through Marias Pass. Elsewhere 
a band of light to moderate snowfall will track north to south 
from northwest Montana through west-central Montana and north- 
central Idaho Wednesday morning through the afternoon, with 
additional snowfall expected. By Wednesday evening, snowfall 
across Lookout, Lolo, and Marias Passes will need to be measured 
with a yardstick!

There are still questions on the evolution of the weather pattern
for Thursday and Friday. The moisture and snow focus does still
look to transition southward but may only linger for a short
period of time during Wednesday night and Thursday morning.
Another weather system is likely to arrive on Friday with higher
snow levels to start and periods of snow for the weekend.

&&

.AVIATION...Radar returns are starting to increase as a warm front
moves into the region. Snow will return during the evening with
widespread lowered ceilings, obscured terrain, and consistently
reduced visibility through the overnight and into Tuesday morning.
Moderate to heavy snow is expected in portions of north-central
Idaho and northwest Montana tonight through at least Tuesday
night. Winter Storm Warnings have been issued to account for the
heavy snow, where low elevations can expect 6 to 10 inches of snow
by Tuesday evening and around 20 inches in the mountains.
Southwesterly winds will increase in the terrain and in 
Grangeville tonight. 

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 9 AM MST Tuesday 
     Missoula/Bitterroot Valleys.

     Winter Storm Warning from 11 PM this evening to 5 PM MST 
     Wednesday Lower Clark Fork Region.

     Winter Storm Warning from 2 AM to 1 PM MST Tuesday 
     Flathead/Mission Valleys.

     Winter Storm Warning from 2 AM Tuesday to 5 PM MST Wednesday 
     West Glacier Region.

     Winter Storm Warning from 11 PM this evening to 5 PM MST 
     Wednesday Kootenai/Cabinet Region.

     Winter Weather Advisory until 9 AM MST Tuesday 
     Bitterroot/Sapphire Mountains.

     Winter Storm Warning from 2 AM to 1 PM MST Tuesday 
     Potomac/Seeley Lake Region.

ID...Winter Storm Warning until 10 AM PST Tuesday Orofino/Grangeville 
     Region.

     Winter Storm Warning until 4 PM PST Wednesday Northern 
     Clearwater Mountains...Southern Clearwater Mountains.

&&

$$