462
FXUS65 KMSO 272041
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
241 PM MDT Mon May 27 2024

.DISCUSSION...On Tuesday, the ridge of high pressure will continue
to amplify and shift eastward as a trough of low pressure deepens
over the West Coast. This will place the Northern Rockies under
moist southwesterly flow. While Tuesday will be the warmest day of
the work week, a lot of factors are pointing towards good
likelihood of afternoon thunderstorms. Pacific moisture, along
with good instability and shear, and a dry lower atmosphere, will
fuel storms capable of producing strong, gusty outflow winds,
heavy rain, lightning, and small hail in the late afternoon and
evening hours. Details on timing and specific threats follow:

Gusty outflow winds: Gusty outflow winds look most likely between
3pm and 10pm MDT, particularly across west-central Montana
including Ravalli, Missoula, Lake, Granite, Powell, Mineral and
Sanders Counties. The probability of seeing storms capable of
gusts over 40 mph within this area is around 40 to 60 percent.
Some high resolution guidance shows the potential (10-20 percent
chance) for a few storms capable of wind gusts over 60 mph.
Outflow winds from storms could cause damage to outdoor property,
trees, and powerlines. One interesting note, the most recent high
resolution models seem to be singling out the Missoula valley for
strong winds late tomorrow afternoon (5pm-7pm time period) with a
nearly 70 percent chance of gusts over 40 mph and a 30 percent
chance of gusts over 50 mph.

Heavy rain: The heavy rain threat seems to increase during the
Tuesday evening hours, most likely between 6pm MDT and midnight.
Forecast models indicate a very moist airmass moving into the
region with precipitable water values approaching 1.00" through
north central Idaho. There is a 40 to 60 percent chance that
thunderstorms will be capable of producing 0.50" in 30 minutes
under the stronger storms. High resolution forecast models even
show a 10 to 20 percent chance of 1.00" per 30 minutes through
portions of Idaho county. Ponding of water in urban areas will be
possible if they take a direct hit. In addition, burn scars and
flood prone basins in Idaho county may be susceptible to debris
flows.

The low over the west coast arrives in the Northern Rockies on
Wednesday, bringing widespread precipitation to the region.
Impacts under this pattern will be characterized by temperatures
5-10 degrees below normal, gusty westerly winds (20-35 mph in
valleys), and widespread shower activity.

Model ensemble solutions are leaning towards a return to high
pressure by next weekend, with about 85 percent showing a broad
ridge over the western U.S.

&&

.AVIATION...High pressure today will keep visibility and ceilings
at VFR across the Northern Rockies with light to moderate winds.
The next chance for impactful weather will be on Tuesday as clouds
increase and there will be chances for afternoon thunderstorms
across the Northern Rockies. The main threat with thunderstorms on
Tuesday will be gusty outflow winds over 35 kts, lightning, heavy
rain and small hail. Thunderstorms are most likely between
28/2100z and 29/0400z.



&&

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

$$