Hamilton, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

965
FXUS65 KMSO 301106
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
406 AM MST Thu Jan 30 2025

.DISCUSSION...

KEY MESSAGES:

-  A major change to more wintry weather is coming Friday and will
   last through the weekend at least.

-  A lot of uncertainty remains with the incoming system with a
   couple of possible scenarios involving snow and freezing rain.

What a 10 day period for Missoula, through Jan 19th our average
temperature was 2.5 degrees above normal for January. Currently,
we are almost 3.0 degrees below normal for the entire month. These
colder temperatures have been present throughout western MT and
Lemhi County ID, excluding the Flathead Valley which has had a
blanket of stratus clouds keeping it warmer. This is important as
these are the antecedent conditions prior to our next system.
Temperatures have been well below normal, which in turn has cooled
sub surface temperatures.

This will change over the next couple days as a warmer and
moister air mass is ushered in from the southwest. There is still
considerable uncertainty with precipitation type in western MT at
the onset of Precipitation Friday. North-central ID there is less
uncertainty as snow levels will be above 3500 feet, snow is
only expected in higher valleys and Whitebird Hill Friday morning.

Western MT is more complicated, today will begin very cold
everywhere but the Flathead Valley. A southerly gradient is
expected to develop which could disrupt many cold pools, except
locations like the Missoula and Flathead Valleys, along with the
valleys of MT-200 and US-2 west of Kalispell, where cold pools
may survive. If they do survive a period of mixed precipitation
will be possible as early as the morning rush hour in NW MT. Plan
accordingly for difficult driving conditions Friday into
Saturday, especially if the precipitation type trends towards
freezing rain or rain freezing on contact with very cold surfaces.
Overnight Friday, travel over Lookout Pass may become very
difficult with snowfall rates in excess of 0.50" per hour, 40%
probability.

Gusty southwesterly winds will begin to downslope valleys on
Saturday as mountains continue with moderate to heavy snow. Snow
levels drop rapidly during the day under a very cold trough. All
locations could end with snow. With the cold ground and some
strong winds, snow squalls are a concern for Saturday afternoon
and evening. Under the pattern that is emerging, the areas of the
most concern for snow squalls currently are from Missoula to
Butte along Interstate-90, then south into the Bitterroot Valley.

Models are in good agreement with the Arctic pushing across the
divide Sunday afternoon. Along the boundary there could be a brief
but heavy period of snow.

Overnight Sunday into Tuesday there is model consensus that a
Arctic overrunning event will happen, there are differences
between models where it will happen. The European Community (EC)
model ensemble is in very good agreement that moderate to heavy
snow will fall in the mountains and valleys from the eastern
Clearwater Mountains of ID, through the Bitterroot and Missoula
Valleys, northeast into the Swan Valley. The GFS ensemble keeps
this area of overrunning further south out of our forecast area.
Our current forecast, driven by the National Blend of Models (NBM)
has trended towards the EC solution. Future forecasts will
hopefully bring a better consensus between models.


&&

.AVIATION...With strong high pressure continuing, low stratus and
fog will be possible across the region. So far, the Flathead and
Mission valleys have experienced the brunt of the lower ceilings
and visibility. A pattern change is expected to start on Friday as
a moist system will bring periods of moderate precipitation to the
region through Saturday.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from Friday afternoon through Monday
     afternoon for Bitterroot/Sapphire Mountains...Lower Clark
     Fork Region...Potomac/Seeley Lake Region.

     Air Stagnation Advisory until 5 AM MST Friday for
     Kootenai/Cabinet Region...Lower Clark Fork Region...
     Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region.

     Winter Storm Watch from Friday evening through Monday afternoon
     for Missoula/Bitterroot Valleys.

     Winter Storm Watch from Friday morning through Monday afternoon
     for Flathead/Mission Valleys...Kootenai/Cabinet Region...
     West Glacier Region.

ID...Winter Storm Watch from Friday afternoon through Monday
     afternoon for Northern Clearwater Mountains...Southern
     Clearwater Mountains.

     Air Stagnation Advisory until 5 AM MST /4 AM PST/ Friday for
     Eastern Lemhi County...Orofino/Grangeville Region.

     Winter Storm Watch from Friday evening through Monday afternoon
     for Eastern Lemhi County...Western Lemhi County.

&&

$$