Hamilton, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

403
FXUS65 KMSO 230815
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
115 AM MST Mon Dec 23 2024

.DISCUSSION...

KEY MESSAGES:

-  Risk for pockets of freezing rain this morning for valleys
   below 4000 feet, mainly affecting western Montana.

-  Pattern will remain active through the week, with mountainous
   terrain receiving persistent snow, affecting travel over mountain
   passes.

Persistent low pressure over the northeast Pacific Ocean is
keeping the upper level jet pointed at the Pacific Northwest.
Shorter wave disturbances will move through the large scale flow,
bringing periods of unsettled weather to the Northern Rockies
throughout the coming holiday week. In general, moisture is
arriving from the southwest, keeping temperatures moderate enough
to support valley rain and mountain snow. While no single
disturbance is looking terribly impressive, mountain snowpack will
benefit as persistence pays off.

The latest disturbance is moving into the Idaho Panhandle early
this morning. Valley locations should expect rain below about 4500
feet. Lookout, Lolo, and Lost Trail Passes could pick up a few
inches of snow by this evening. The higher elevations of most
mountain ranges will see a little more. Freezing rain will remain
in the forecast this morning for valleys able to hold on to
colder temperatures such as the Libby area and the Flathead,
Missoula, and Bitterroot Valleys, as well as the Elk City, ID
area.

The upper level jet will split on Tuesday, with the Northern
Rockies stuck in the middle. This scenario will keep dynamics for
lift out of the picture. Moisture will still be present though,
so light snow showers stay in the forecast for the Clearwaters and
along the Idaho-Montana border where the terrain will provide
some vertical motion. The active pattern takes Christmas Day off,
and gets back to work on Thursday.

Thursday into the weekend is when things become more interesting
as a more potent weather system moves in from the west. As of now,
this system also looks cold enough to produce snow down to valley
floors. There is much higher confidence that moderate to heavy
snowfall will occur above 4500 feet during a period from late
Thursday through Sunday (Dec 29), which could create difficult
travel over mountain passes for those traveling during the
holiday travel period. The most snowfall looks .

For I-90 over Lookout Pass, there is currently an 80% chance of
at least 6 inches of snow accumulating by Saturday afternoon, and
a 60% probability of one foot of accumulation. Both Lolo Pass and
Lost Trail pass show a 65% probability of 6 inches occurring by
Saturday afternoon.



&&

.AVIATION...Mixed precipitation starting early this morning by
about 23/1000Z to 23/1200Z will affect all terminals across the
Northern Rockies air space. Expect rain, with slight chances for
freezing rain at KGPI and KMSO. Precipitation will result in
decreases in visibility and ceiling through this morning and will
obscure terrain across all mountain ranges in the Northern
Rockies.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$