FXUS65 KMSO 201821

AFDMSO



Area Forecast Discussion

National Weather Service Missoula MT

1221 PM MDT Sat Jun 20 2026



.DISCUSSION...



KEY MESSAGES:



- Thunderstorms return to Lemhi County, Idaho, and southwest

  Montana with the weather pattern during weekend, bringing 

  lightning and brief, erratic wind gusts



- Warming trend Tuesday through Thursday



- Cooler and showery conditions expected next weekend



A disturbance passing to the south of our region will interact

with another more northern disturbance that will drop out of 

British Columbia. Shower and thunderstorm activity is likely 

across northwest Montana this afternoon and evening, along with 

ongoing shower and thunderstorms across southwest Montana and 

southeast Idaho. In addition, a few storms could develop as far 

north as Missoula and up to the Seeley Lake/Ovando region. Any 

storms that occur today will be capable of producing gusty erratic

winds, lightning, and brief heavy rain. The shower activity is 

expected to diminish after sunset this evening. 



The British Columbia disturbance will continue to track along the

Canadian border on Sunday, keeping the chance for wrap-around 

shower activity across northwest Montana. It will also bring in 

cooler air, causing temperatures to be near seasonal averages for 

Sunday and Monday.



A ridge of high pressure will be building over the region Tuesday

through Thursday. Temperatures will be steadily climbing each day

with Wednesday and Thursday being the warmest days so far this 

year. Most valley locations should be in the upper 80s to low 90s 

by Wednesday afternoon, with the lower elevation valleys of north

central Idaho breaking 100 degrees.



The vast majority (over 75%) of the long term models are showing 

a trough of low pressure moving into the Pacific Northwest by next

weekend, causing cooler conditions along with widespread shower 

activity.



&&



.AVIATION...Moisture will continue across Lemhi county, ID and 

southwest Montana today, causing scattered showers. Instability 

this afternoon will lead to the potential development of 

thunderstorms that could impact KSMN and KBTM. These storms will 

be capable of producing gusty erratic winds, lightning, and brief

heavy rain. KMSO, KHRF, and KGPI have a lower probability of 

being impacted by these storms. The shower activity is expected to

diminish after sunset this evening.



&&



.MSO WATCHES/WARNINGS/ADVISORIES...

MT...None.

ID...&&



$$