698
FXUS65 KMSO 270905
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
305 AM MDT Sun Jul 27 2025

.DISCUSSION...

KEY MESSAGES:

-  KMSO Radar or the local Missoula MT weather radar will continue
   to be offline due to scheduled maintenance through 1st week of
   August.

-  Thunderstorm chances continue each day, but Monday through
   Wednesday may become terrain driven.

-  There is a 30 to 40 percent probability for strong thunderstorm
   outflow gusts in excess of 40 mph today.


An area of showers and thunderstorms moved into north-central ID
around midnight and will allow for some nocturnal storms through
mid-morning today, spreading eventually into western MT.

The question now becomes how much residual cloud cover will we
have? With sufficient clearing an analysis of the atmosphere
demonstrates increasing moisture today compared to Saturday.
Threats for today will continue with gusty outflow winds with a 20
to 30% chance of gusts 40+ mph, generally in the Bitterroot and
Missoula Valleys, and I-90 east of Missoula. The increased
moisture and modest shear will allow for small hail and isolated
heavy downpours. Coverage of storms will expand through all but
far NW MT, IE the Yaak and NW portions of US-2.

The overall risk of flash flooding remains low over recent burn
scars and flood-prone terrain due to sufficient steering flow.
However, isolated runoff issues cannot be entirely ruled out.

Overnight Sunday into Monday the signal for nocturnal
thunderstorms is stronger than this evening, so an adjustment to
probability of thunderstorms will be made in the forecast to
reflect the potential.

Monday through Wednesday the forecast becomes intriguing and
challenging. The models would suggest weak high pressure folds
over the region. At the same time atmospheric moisture continues
to increase. Showers and thunderstorms will continue but may
require the lifting of higher terrain to initiate. Also, steering
winds that are currently 35 to 40 mph, will decrease 20 to 25
mph. Any heavy showers that form will move slower over any
location, we`ll continue to monitor concerns for flash flooding,
mainly in vulnerable drainages and new burn scars. The gusty wind
outflow threat will decrease except in cases of thunderstorm cores
that collapse into valleys due to lack of lift. As HIRES models
become available (48-hours or less) they may depict weak waves
ejecting off the overall Pacific trough, these would allow for
valley storms.

By Thursday, atmospheric moisture remains elevated. Models vary
widely on timing and actual feature, but almost all depict
atmospheric waves moving through the region pushing the ridge
east. This will add lift and produce cooler temperatures, with
widespread shower and thunderstorm activity. More to come as the
forecast evolves.




&&

.AVIATION...An area of showers has moved into north-central ID.
Little precipitation is being observed at local weather stations,
however brief terrain obscurations with some lightning can be
expected. This area of showers moves into Western Montana later
this morning.

This afternoon, the atmosphere destabilizes again and strong
storms develop at KSMN, KHRF, KMSO, and KBTM between 27/1900z and
28/0300z. The wide range in times reflects the potential for two
distinct periods of storms to form, early and then again late
afternoon. Gusty outflow winds up to 40 kts and heavy downpours
reducing visibilities are possible, with a low probability of
small hail.


&&

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

$$