277
FXUS65 KMSO 131954
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
154 PM MDT Sun Jul 13 2025

.DISCUSSION...

KEY MESSAGES:

-  Moderate heat risk impacts across low elevations of north-
   central Idaho and western Montana this afternoon, and also on
   Monday in Idaho.

-  Strong northeast winds 30-45+ mph Monday and Monday night, with
   risk for spotty power outages, tree damage, and dangerous
   conditions for boaters on area lakes of northwest Montana.

-  Strong northeast winds 30 to 45 mph are possible across Lemhi
   County Tuesday evening.

The hottest temperatures of the week are expected today, as highs
reach into the low-100s for lower elevations of central Idaho and
low/mid-90s across western Montana valleys. These temperatures
will bring a moderate risk of heat impacts. Consider practicing
heat safety by drinking plenty of fluids, and resting in shaded or
air conditioned environments when working outside. Furthermore,
breezy westerly winds will lead to elevated fire weather
conditions.

Latest weather model guidance is showing a strong cold front
plowing southwards through northwest Montana Monday evening.
Three-hour pressure rises range from 6 to 11 millibars which is
impressive for this time of year! As mentioned in the early
morning discussion, mountain wave activity could enhanced
localized wind gusts, reaching well over 40 mph. We have issued
high wind watches in these areas for Monday evening through
Tuesday morning. These types of winds could cause weakened tree
limbs to break off, or even cause some treefall. If you are
camping or recreating outdoors, avoid setting up tents or campers
near trees. Also you may want to avoid recreating on area lakes.
The rainfall on Tuesday morning could help stabilize the wind
gradient a bit across northwest Montana.

Thunderstorms are the next impact with this system. High
resolution guidance depict storms forming along the cold front
from Yaak to Eureka to Glacier National Park Monday afternoon and
evening. The HRRR model depicts small hail generally less than
0.50" in diameter with the stronger storms. As this front pushes
south, isolated storms could be possible Monday night. Also heavy
downpours and lightning can be expected. Behind the front, while
northeast winds continue in Glacier National Park, heavy rain showers
are possible over the higher terrain of the Divide. There could be
some sloughing off of some debris on the upper portions of the Going-
To-The-Sun Road, but it would occur during the overnight hours
Monday night. One other note is the atmospheric moisture
content(Precipitable water)that this system will be able to work
with is around +3 standard deviations, or around 200 percent of
normal. So any embedded storm could be a decent rain producer. On
Tuesday afternoon and evening thunderstorm chances shift
southwards towards southwest Montana and Lemhi County.

The cold, wet and windy conditions in the backcountry will be
another impact. Even with the downsloping northeast winds,
rainfall will still occur at times. Once the main upper level
forcing/lift weakens, there could be more dry periods by Tuesday
morning across northwest Montana.

The wind gradient may be strong across southern Idaho County,
southern Ravalli County and Lemhi County Tuesday evening. With
nightfall, there could be enhanced wind through the channeled
terrain in the Bitterroot Mountains, generally gusting 30 to 45
mph. This gradient is expected to relax with time by Wednesday
morning.

By Wednesday morning there will be a 1022 millibar high pressure
over western Montana. With any clearing, some of the high valley
locations could dip down into the lower 30s along and west of the
Divide... 45 percent chance of that occurring in Polebridge, 33
percent chance in Olney, and 52 percent chance between Anaconda
and Georgetown Lake. These probabilities are similar for Thursday
morning as well.




&&

.AVIATION...Surface observations reveal gradually increasing
winds this afternoon with gusts of 15-20 kts expected through the
afternoon. These winds will decrease through the evening. A
weather system approaches the region on Monday, and west winds
are forecast to begin in the morning, increasing to 15-25 kts by
the afternoon. A strong front, arriving from the northeast, will
bring an abrupt wind shift to northeast Monday evening through
Monday night. Wind gusts of 35-45 kts will be common with the
frontal passage.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Watch from Monday afternoon through Tuesday morning
     for Kootenai/Cabinet Region...West Glacier Region.

     High Wind Watch from Monday evening through Tuesday morning for
     Flathead/Mission Valleys.

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

&&

$$