398
FXUS65 KMSO 211054
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
354 AM MST Fri Feb 21 2025

.DISCUSSION...

KEY MESSAGES:

-  Increased snowmelt and runoff Saturday into Monday, bringing
   the risk of minor flooding of low-lying and poor drainage areas
   and to small streams and creeks from potential ice jam
   releases.

-  Widespread rain and high elevation mountain snow, Sunday into
   Monday.

-  Areas of freezing rain Saturday and Sunday morning across
   western Montana with cold subsurface ground temperatures in
   place.

A warming and drying trend will take hold today as high pressure settles
over the region. By Saturday, an incoming disturbance will bring scattered
showers across the Northern Rockies. Rising snow levels will keep snowfall
limited to higher elevations, while valleys will likely experience a wintry
mix.

Looking ahead to Sunday and Monday, forecast models continue to signal a
prolonged atmospheric river event, delivering widespread precipitation and
pushing snow levels above 6,000 feet . Clearwater County and areas near the
northwest Montana-Idaho border have a 90% chance of receiving over an inch
of rain within 48 hours, with some higher terrain in north-central Idaho
potentially exceeding two inches.  While most locations will see
precipitation fall as rain, the terrain above 6000 feet will pick up a
significant amount of snowfall of over a foot.

With temperatures expected to remain above freezing in most valleys from
Saturday night through Tuesday, melting low-elevation snow combined with
steady rainfall will lead to ponding in poor drainage areas, localized
minor flooding, and ice breakups on small creeks and streams. Clearing snow
from drainage areas ahead of time may help reduce potential impacts.

Another concern is the risk of icy conditions, particularly overnight
Saturday and Sunday. Although air temperatures may rise above freezing,
many western Montana valleys still have subsurface temperatures 2 to 5
degrees below freezing. This could result in rain freezing on contact,
creating hazardous conditions, especially on secondary roads with lingering
snow cover. Travelers should be prepared for slick spots, particularly on
untreated surfaces.

Another disturbance is expected late Monday night into Tuesday.  Snow
levels will initially start around 5000 feet, but will drop once again on
Tuesday morning as a cold front moves through the region.  By this point,
the main moisture source will be cut off, but lingering snow showers will
likely exist.  In fact, some forecast models are showing a pattern that
could be conducive for snow bands Tuesday morning.

Forecast models are coming into agreement in a ridge of high pressure
developing over the region by late Wednesday through the end of the work
week.  Relatively mild conditions would be possible under this pattern,
though it may also allow for the development of low clouds and
fog.

&&

.AVIATION...Satellite imagery this morning reveals a mid level
cloud deck spread across most of western Montana, which has
largely inhibited any fog formation. Clearing has occurred
through north central Idaho however, with areas of fog along the
Highway 12 corridor from Lolo Pass to Grangeville. High pressure
today will keep winds relatively light with some breaks in the
clouds possible by this afternoon.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch from Saturday afternoon through Monday afternoon for
     Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...
     Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower
     Clark Fork Region...Missoula/Bitterroot Valleys...
     Potomac/Seeley Lake Region...West Glacier Region.

ID...Flood Watch from Saturday afternoon through Monday afternoon for
     Lower Hells Canyon/Salmon River Region...Northern
     Clearwater Mountains...Orofino/Grangeville Region...
     Southern Clearwater Mountains.

&&

$$