426 
FXUS65 KMSO 091005
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
405 AM MDT Tue Sep 9 2025

.DISCUSSION...

KEY MESSAGES:

-  Thunderstorms each day through Thursday featuring gusty outflow 
   winds and heavy rain, focused afternoon/evening hours 

-  80% chance for wetting rains most areas, except 30 to 50%
   chance for less than 0.10" from Lemhi County to Southwest
   Montana(Butte and south), and far Northwest Montana. 

-  40-50% chance for an inch or greater of total rainfall across
   Clearwater and Idaho Counties, and from Seeley Lake northwards
   to Glacier National Park through Saturday morning.

-  Patchy morning fog could pose an issue late week due to 
   increased moisture from rain. 

The upper low over California, Nevada and Oregon today, will 
begin to split into multiple pieces: the southern energy digging 
into southern California, and a northern piece breaking off and 
wobbling northeastwards towards central Montana by 
Friday/Saturday. This will bring widespread showers and 
thunderstorms to the Northern Rockies Thursday into Friday. 

In the short-term, a weak wave has initiated a few nocturnal
thunderstorms early this morning near Plains and points northeast.
A more organized wave is expected to move north across our region
today, and current satellite and radar imagery depicts this 
across southern Idaho, edging closer to Idaho and Lemhi counties
as of 4 am MDT. High resolution weather models depict widely 
scattered storms tracking south to north into this afternoon and 
evening. The main threats will be gusty winds to 40 mph, heavy 
rain, small hail, and lightning. If the storms hit burn scars or 
flood prone areas, debris flows or flash flooding could occur. 
Yesterday, storms produced 1 to 1.40 inch per hour rates between 
Happy's Inn and Flathead Lake. One storm just dumped 0.35" in 15
minutes at Lakeside. Atmospheric moisture levels this week will 
generally be around 200% of average, so thunderstorms will be able
to produce a ton of rain in a short amount of time. 

The latest HRRR smoke model depicts residual smoke moving up here
from the central California fires later today. Much of this will
be lofted into the atmosphere, so higher elevation locations 
could experience an uptick in smoke. 

With the anticipated moisture increase, and cooler temperatures by
Friday, fog could become more of an issue especially as we might
get more clearing at times by Friday and Saturday nights with the
low pressure system pulling away.

Just when you think we might get a break(Sunday) from the 
moisture when this first system pulls away, another trough is 
forecast to move onshore by next Monday and bring another shot of 
widespread precipitation!


&&

.AVIATION...Thunderstorms will develop by 18z (12 pm MDT) today
and continue through midnight tonight across the Northern Rockies.  
Gusty outflow winds to 35 kts, small hail, heavy rain, lightning,
and brief terrain obscuration will be the concerns. Watch for 
patchy valley fog development tonight, especially where rain 
occurs today. Showers and thunderstorms are expected again on
Wednesday.

&&

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

$$