Wind Advisory 9, NWS Missoula, MT

053 
WWUS75 KMSO 240150
NPWMSO

URGENT - WEATHER MESSAGE
National Weather Service Missoula MT
750 PM MDT Fri Aug 23 2024

IDZ009-010-240300-
/O.CAN.KMSO.WI.Y.0009.000000T0000Z-240824T0300Z/
Western Lemhi County-Eastern Lemhi County-
750 PM MDT Fri Aug 23 2024

...WIND ADVISORY IS CANCELLED...

The threat has ended.

$$

Area Forecast Discussion
National Weather Service Missoula MT
158 AM MDT Fri Aug 23 2024

.DISCUSSION...

Key Messages:

- Thunderstorms return this afternoon. Few strong/severe
  thunderstorms into early evening, with potential gusts over 60
  mph along with hail.

- Strong southerly wind gusts 35-45 mph for Lemhi County and
  southwest Montana today.

- Much cooler and showery this weekend.

- Frost potential Monday morning, again late next week.

Here are the details:

Southerly flow really picks up today as a large Pacific trough
comes onshore. The first impact will be strong southerly winds
(gusts 30-45 mph) late morning through early evening, especially
across Lemhi County and southwest Montana. Thunderstorms will also
return by early afternoon, quickly spreading northward. Shear and
instability parameters will be sufficient for a few strong/severe
storms. Isolated severe wind gusts over 60 mph are showing up in
some high resolution models, especially along the Divide and in
northwest Montana. A secondary threat will be hail. Winds and
thunderstorms diminish quickly by sunset.

The Pacific trough comes through the Northern Rockies over the
weekend with much cooler temperatures (valley highs in the 70s for
north-central Idaho and 60s/low 70s across western Montana). It
will also be showery and breezy. There is a 30-40% probability of
over 0.10 inch of rain for valleys north of I-90, 50-60% from I-90
southward. The heaviest rain totals are forecast for the terrain
of north-central Idaho and west-central Montana with average
values of 0.25-0.45 inch.

The upper level flow becomes zonal (westerly) for Monday afternoon and
Tuesday which allows for warming and drying across the Northern
Rockies. This flow pattern does allow for gusty westerly winds to
potentially mix down to the surface during the afternoon and
evening hours. There is good agreement on a trough dropping out of
Canada by Wednesday for a chance of showers and a brief cool down.
Snow levels drop to 7500 feet in the Glacier Region, thus a light,
fresh coat of snow is possible on the higher peaks. Behind the
trough, a ridge builds up again (85% chance) with high
temperatures warming to seasonable levels, along with drier
conditions.

Another potential impact is frost. Monday morning will feature a
50-70% probability of frost for the higher valleys along the
Divide such as Seeley Lake and Deer Lodge. There is a 10-20%
chance for Butte and the Bitterroot Valley. Thursday morning looks
to be slightly cooler with frost probabilities of 30% for the
Bitterroot Valley, 10-20% for Missoula and Kalispell.

&&

.AVIATION...Southerly winds really pick up late this morning into
the afternoon with gusts of 25-40 kts for terminal sites.
Shear and instability will also increase as a disturbance lifts
across the Northern Rockies and interacts with monsoonal moisture.
Scattered thunderstorms look to initiate around 23/20Z and quickly
spread northward. Isolated severe wind gusts over 50 kts are
showing up in some high resolution models, especially along the
Divide and in northwest Montana. A secondary threat will be hail.
Southerly winds will be replaced by westerly winds later in the
afternoon as a cold front presses west to east across the region.
Winds and thunderstorms diminish quickly by sunset.

&&

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