622
FXUS65 KMSO 292039
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
239 PM MDT Mon Jun 29 2026

.DISCUSSION...

KEY MESSAGES:

- Flooding of small streams and creeks due to ongoing heavy rain
  is imminent or occurring in the Mission valley and in Glacier
  National Park

- Strong showers and thunderstorms capable of rainfall rates of
  0.50" to 0.75" per hour possible for locations along and north
  of I90 in northwest Montana through this evening

- Widespread heavy rain tapers off late tonight, however an active
  pattern supportive of showers and thunderstorms with locally heavy
  rain continues through Friday

Widespread prolonged rainfall continues this afternoon as
anomalous moisture (200 percent of normal) continues to rotate
around an upper level low pressure system moving slowly through
central Montana. Observed 24 hour precipitation amounts of 1 to 2
inches of rain are common across much of western Montana and
north central Idaho with focused amounts of 3 to 6 inches
occurring in the higher terrain along the Continental Divide in
Glacier National Park as well as the Mission and Swan Ranges. With
additional amounts of 1 to 3 inches of rain possible through
Tuesday morning in these locations, areal flood warnings have been
posted for small streams and creeks of Glacier National Park and
in the Mission valley. High resolution forecast models show an
area of instability through portions of Sanders, Lake, Lincoln,
Flathead and Missoula counties this afternoon and evening, which
may allow for convective precipitation (thunderstorms and strong
showers) to develop. This activity will be capable of 0.50 to
0.75 inch per hour rainfall rates, which could accentuate ongoing
flooding or potentially impact additional flood prone basins/burn
scars.

Precipitation intensity is expected to decrease late tonight into
Tuesday morning as the low pressure system exits the region.
However, a general trough with a wave of energy will move through
the region Tuesday afternoon and evening. Anomalous moisture will
remain in the atmosphere, which may allow for thunderstorms
capable of localized heavy rain. This will mainly be focused
through Idaho county, Lemhi County and southwest Montana.

A moderating trend is expected later this week with possible
thunderstorms each day. With the added low-level moisture from all
the rain, this could enhance instability each day through Friday.

&&

.AVIATION...Low pressure continues to spin east of the Continental
Divide this afternoon, sending wraparound moisture into the
Northern Rockies airspace. Precipitation will continue, lowering
visibility and ceilings into Tuesday morning. Heavier rainfall
producing short bursts of 0.50 inches per hour rates will last
through about 30/0400Z, reducing visibility down to IFR at times.
Expect terrain to be obscured over the entire Northern Rockies
airspace well into Tuesday. Fog could also form over KMSO and
KGPI early Tuesday morning, though confidence was not yet high
enough to include fog in the 29/1800Z TAFs.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch through late tonight for Flathead/Mission Valleys...
     West Glacier Region.

ID...None.
&&

$$