National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KMSO 150955
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
355 AM MDT Mon Apr 15 2024

.DISCUSSION...We had some pretty good slow-moving thunderstorms
last evening that brought heavy rainfall to portions of north-
central Idaho and also in Mineral County, Montana. In fact,
Highway 162 southwest of Kamiah,Idaho was closed due to a
mudslide near Fort Misery Road. Radar rainfall estimates showed
between 1 and 2 inches fell in that location in a matter of a few
hours! Also to note, thunderstorms formed over the higher terrain
west of Flathead Lake, then shifted over the lake just before
midnight...producing a few lightning strikes and gusty south winds
to 35 mph in Kalispell. High temperatures yesterday were well
into the 70s with a few 80s...only several degrees away from tying
with the daily records. It sure felt summer-like.

If yesterday was summer, then today will be more like spring and
tomorrow through Thursday will be back to winter for some folks in
the Northern Rockies. With the atmosphere in transition today
with the influx of cooler air, a decent westerly pressure/wind
gradient will set up over the region. Even though temperatures
will rise into the lower to mid 60s for valleys today, the gusty
winds between 25 and 35 mph later this afternoon and evening will
make it feel kind of chilly...enough to possibly need a wind
breaker! A 1 to 2 foot chop is expected on area lakes, especially
on parts of Flathead Lake. The stronger wind probabilities are
higher more towards the western part of the lake towards Big Arm
and also in the northwest where wind gusts near or over 25 mph are
more likely.

Then in comes the well-advertised, cold upper level trough on
Tuesday...the mountains will feel it first as temperatures plummet
down into the teens and 20s with wind chill temperatures in the
single digits Tuesday morning. As the day wears on, high
temperatures will struggle to get to 50 degrees for many locations
and when you combine the gusty westerly winds, it`s going to feel
even more chilly than Monday! Snow showers can be expected,
especially later Tuesday into Tuesday night across northwest
Montana. Models depict a backdoor type cold front feature with
gusty northeast winds from the Glacier region into the Flathead
Valley towards Wednesday morning, and also snow down to valley
floors across western Montana. The statistical ranges for snow
amounts range from a quarter of an inch up to an inch in the
valleys, then between 2 to 5 inches along the Divide including
Marias Pass. The upper end depicts close to 9 inches in the
higher elevations of Glacier National Park.

With such an unstable atmosphere, snow showers will persist during
the day on Wednesday through Thursday. So there could be periodic
slush at area passes and even for lower elevation travel corridors
like Evaro Hill and upper benches of the Bitterroot, and points
east across southwest Montana.

By Thursday and Friday, a milder ridge will build over the Pacific
coast into Washington and Oregon. This will present lower pressure
due to the milder conditions there, but meanwhile, colder high
pressure over central Montana will set up a moderately strong
north to east wind gradient over Idaho and western Montana. This
may need to be watched as gusty east winds could be an impact to
area lakes. There is a 20 to 30 percent chance for lingering
mountain snow showers on Thursday.

Models diverge for next weekend (Apr 14-15)...so we look to the
ensemble cluster analysis to see if there are any insights.
Setting the stage leading up the weekend, a temporary high-
latitude omega blocking pattern sets up(which is part of the
reason why the cold trough stays with us for about 4 days)and
models have different takes on how the energy pinwheeling around
the next northeastern Pacific trough will evolve. Around 70% of
the ensemble members depict that energy moving over the region by
Sunday which would bring unsettled and cooler weather for us. In
fact, the NBM forecast ramps up the chance for precipitation for
us. But to be fair, the other 30% of the members (which is still a
plausible outcome), depict a milder and dry ridge over us
followed by a cooler trough into the following week. Let`s hope
that after this chilly week, that the milder pattern will come to
fruition!

&&

.AVIATION...The main story will be the increasing westerly winds
across the region both today and Tuesday. Lingering showers can
be expected over the southern Clearwater and Bitterroot mountains
through early afternoon today. Otherwise gusty winds will ramp up
by this afternoon. Gusty winds will continue in the higher
elevations tonight through Tuesday morning, especially over the
Divide.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Lake Wind Advisory from noon today to 9 PM MDT this evening for
     Flathead/Mission Valleys.

ID...None.
&&

$$