972
FXUS65 KMSO 280813
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
213 AM MDT Tue May 28 2024

...STRONG THUNDERSTORMS CAPABLE OF GUSTY WINDS, HEAVY RAIN THIS
AFTERNOON/EVENING ...

.DISCUSSION...The ridge of high pressure over the Northern Rockies
on Monday will shift eastward today as a trough of low pressure
deepens over the West Coast. This will place the Northern Rockies
under moist southwesterly flow. While today will be the warmest
day of the work week, a lot of factors are pointing towards the
development 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 damaging wind gusts over 60
mph. Outflow winds from storms could cause damage to outdoor
property, trees, and powerlines.

Heavy rain: The heavy rain threat will 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 pressure system currently over the west coast will
arrive in the Northern Rockies on Wednesday, bringing widespread
precipitation to the region. Expect temperatures 5-10 degrees
below normal, gusty westerly winds (20-35 mph in valleys), and
widespread shower activity. Upper level flow turns northwesterly
on the tails of the departing trough on Thursday. The upper level
jet will remain in a favorable position for gusty west winds to
mix down to the surface. Precipitation will mostly be limited to
the Continental Divide.

Model ensemble solutions are leaning towards high pressure or
westerly flow by next weekend.


&&

.AVIATION...Widespread thunderstorms will be the primary impact to
aviation this afternoon from about 28/2100Z through about
29/0400Z. The main threat with thunderstorms today will be
erratic, gusty outflow winds over 35 kts, lightning, and CIG/VIS
reductions due to heavy rain and small hail. Cloud cover, gusty
winds, and chances for rain will remain in the TAFs through
Wednesday under a trough of low pressure.


&&

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

$$