163
FXUS65 KMSO 261909
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
109 PM MDT Sun May 26 2024

.DISCUSSION...GOES Satellite imagery this afternoon shows numerous
fair weather cumulus clouds across the Northern Rockies. Forecast
soundings suggest surface heating will allow for just enough
instability for isolated showers to develop across eastern
portions of Lake and Flathead Counties. Otherwise, valley areas
can expect a mix of clouds and sun through the rest of the
evening.

A significant warming trend remains on track Monday into Tuesday
as high pressure amplifies across the Great Basin and Northern
Rockies. Confidence is high (probability >90%) for temperatures to
reach into the 80s across valleys in western MT, with the lowest
elevations in Idaho and Clearwater Counties hitting 90.

Forecast models continue to highlight an increased risk for strong
to potentially severe thunderstorms late Tuesday afternoon and
evening. A Pacific trough will move onshore along the OR/WA coast,
with atmospheric moisture, instability, shear, and lift within
southwesterly flow creating a favorable set up for thunderstorms
to develop across northeast OR during the early afternoon.
Guidance suggests storms will then track northeastward into
central Idaho and west-central and northwest Montana during the
evening hours. The probability for strong thunderstorms,
characterized by gusts greater than 40 mph, brief heavy rain, and
small hail (0.75" or less in diameter), has increased into the
20-30% range across central Idaho and northwest Montana.

Forecast details Wednesday into Thursday are beginning to become
more clear. Ensemble guidance is trending away from a closed low
scenario, with 70% of members suggesting a progressive trough
passage, as seen in the 12z GFS/ECMWF. Impacts under this pattern
will be characterized by temperatures 5-10F below normal, gusty
westerly winds (20-35 mph in valleys), and widespread shower
activity, with snow levels of 5,500-6,500 feet. The closed low
scenario as seen with 20% of the members still brings the
possibility for more widespread precipitation, with snow levels
falling closer to 4,000-5,000 feet and pass level travel impacts.

In the far extended, the dice are loaded towards above normal
temperatures during the first week of June. This is well supported
by ensemble means in strong agreement for high pressure across the
Rockies, with a trough of low pressure remaining well off the west
coast. /Lukinbeal

&&

.AVIATION...Satellite imagery as of 26/1900Z shows widespread
fair weather cumulus clouds tracking west to east across the air
space. Westerly flow across mountain barriers is contributing to
the development of mountain wave activity. Surface heating this
afternoon will contribute to shallow instability across Flathead
and Lake Counties, where isolated showers will periodically
obscure terrain. Westerly wind gusts will continue through
27/0200-0400Z, with gusts of 15-20kts for area terminals.
Stronger gusts of 25-30kts are expected along the divide and over
the terrain. /Lukinbeal

&&

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

$$