Hamilton, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

276
FXUS65 KMSO 141928
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
128 PM MDT Mon Jul 14 2025

.DISCUSSION...

KEY MESSAGES:

- Hot today with risk for heat related impacts in north-central
  Idaho

- A potent storm with unusually cold, wet, and windy conditions
  this evening into Tuesday.

- Mostly dry rest of the week, warming back up to near and above
  normal.

Hot temperatures continue this afternoon with many locations warming
well into the 90s (triple-digits in the valleys of north-central
Idaho).

Satellite and webcam imagery this afternoon shows a dispersed
area of elevated smoke drifting slowly eastward out of the state
of Washington due to active wildfires in that region. Surface-
based air quality observations indicate some areas of
deteriorating air quality toward the Moderate category in far
northwestern Montana.

A very unusual storm for this time of year is forecast to move
into the Northern Rockies later this evening through Tuesday. An
upper-level disturbance is noted on water vapor imagery slowly
moving south and east through British Columbia. This disturbance
is pulling in anomalous amounts of precipitable water, near and in
excess of 1, from the Pacific Ocean. HYSPLIT backward trajectory
modeling, for upstream locations, helps identify the Northern
Pacific / Canadian Arctic source of the unseasonably cold air
which is being pulled in on the backside of this disturbance.

As the upper level trough swings through the Canadian border later
this evening, the mid-level low continues to amplify and nearly
cuts off completely from the associated upper level jet as it
pushes into our region. At the surface, a strong cold front will
continue to mature becoming increasingly thermally-packed. This
front will induce a strong northeasterly to southwesterly pressure
gradient across the divide through much of the day on Tuesday
forcing north and easterly winds over and through mountain gaps
similar to a wintertime Arctic cold front. In this environment,
stronger thunderstorms will be able to produce near severe-level
gusts with background winds already elevated in the 20-30 mph
range. Recreators on area lakes should heed wind advisories due to
the potential for large waves and generally choppy/unfavorable
conditions.

Ample moisture availability will help induce shower and
thunderstorm development overnight into Tuesday with heavy
rainfall and small hail potential. There is concern for localized
flooding due to heavier rainfall and mudslide or debris flows in
steep terrain or within and downstream of burn scar perimeters. A
wide range in potential rainfall accumulation exists due to the
convective nature of showers. Generally, 0.2-0.5" of rainfall is
expected across a widespread area north of I-90 with some
locations potentially seeing up to 2.0" of rainfall such as
Glacier N.P., nearby mountains of northwest Montana, and along the
Continental Divide. Some snow may mix down as low as 8,500ft in
the Glacier Region though widespread measurable snowfall remains
unlikely.

A 20-30 degree drop in daytime highs from today to tomorrow will
bring some locations close to record cool high temperatures for
the date. Backcountry users should take into account the cold,
wet, and windy conditions to reduce any risk of prolonged exposure
or hypothermia.

Heading into the rest of the week, a moderating trend in the
weather will follow with daytime highs back near and above normal.
Another disturbance, albeit almost completely dry, will pass
through the region on Thursday bringing another slight uptick to
winds. Warming continues into the weekend.

&&

.AVIATION... A disturbance dropping into the Northern Rockies
from Canada continues to drive gusty winds of 20-30 knots across
north-central Idaho and western Montana. Expect a significant
change later this afternoon or early evening as a potent cold
front sweeps through. This front will usher in strong
northeasterly winds to Kalispell (KGPI), with gusts projected to
intensify to 35-45 knots beginning between 15/0300-0500Z. The
northeasterly wind shift will progress southward throughout the
evening and overnight, eventually reaching Missoula (KMSO) and
Butte (KBTM) by early Tuesday morning. In addition to the strong
winds, sufficient instability accompanying the frontal passage
will spark thunderstorm development across northwest Montana,
including the Kalispell (KGPI) area. These storms will be capable
of producing small hail, heavy rain, and frequent lightning.





&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Wind Advisory from 5 PM this afternoon to 2 PM MDT Tuesday for
     Flathead/Mission Valleys...Kootenai/Cabinet Region...West
     Glacier Region.

     Wind Advisory from 9 PM this evening to 8 PM MDT Tuesday for
     Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...
     Lower Clark Fork Region...Missoula/Bitterroot Valleys...
     Potomac/Seeley Lake Region.

ID...Heat Advisory until 8 PM PDT this evening for Lower Hells
     Canyon/Salmon River Region...Orofino/Grangeville Region.

&&

$$