FXUS65 KBOI 210845

AFDBOI



Area Forecast Discussion

National Weather Service Boise ID

245 AM MDT Mon Sep 21 2026



.KEY MESSAGES...

- Mostly dry with warming temperatures through Thursday.



- Chance of showers and thunderstorms Tuesday, mostly across

  higher terrain of southwest Idaho.



- Cooler temperatures heading into this weekend with a chance 

  of precipitation across SE Oregon and portions of SW Idaho 

  Friday.



&&



.SHORT TERM /Through Wednesday Night/...

Broad upper ridging will keep warm and dry conditions over the

region on Monday. This morning, some mountain valley fog is

possible in Central Idaho high terrain. But as the sun rises in

clear skies temperatures reach 5-10 degrees above normal, or

about 5 degrees warmer than Sunday. An eastward shift in the 

ridge axis on Tuesday will allow for a closed low to lift 

northeastward through the Great Basin. This will bring a 20-30% 

chance of showers and thunderstorms to higher terrain along the 

Idaho/Nevada border, the Central Idaho mountains and the 

mountains in Baker County Tuesday afternoon. Temperatures may be

a degree or two cooler on Tuesday compared to Monday, but a 

general warming trend continues into Wednesday as the cut off 

low moves east, heights rise, and stronger warm southwesterly 

flow aloft moves in.



&&



.LONG TERM /Thursday through Monday/...

A ridge will remain over the area on Thursday. Thursday will be

the hottest day in the 7-day period, with temperatures near 90

degrees in lower elevations and 80 degrees in higher elevations. 

A trough moves into the Pacific NW Friday/Saturday with cooler 

temperatures and increased chances (15 to 25 percent) of 

precipitation this weekend. Precipitation chances will be 

highest in Northeastern Oregon and West-Central Idaho, with 

generally dry conditions as one approaches the Nevada border. 

Temperatures fall to near normal on Friday, and 5 to 10 degrees

below normal on Saturday and Sunday. The temperature drop may

shift fully to Friday or Saturday as synoptic models come into

better agreement on the cold front passage, causing a sharper

cool off on Friday or prolonged warmness on Friday respectively.

Cooler temperatures remain through the weekend into next Monday

as a trough axis entrenches itself along the coast and the jet

stream stays overhead.



&&



.AVIATION /06Z Monday through Tuesday/...

Issued 1118 PM MDT SUN SEP 20 2026

VFR. Patchy mountain valley fog overnight through Monday 

morning, mainly near KMYL. Surface winds: mainly variable or 

S-SE 5-10kt overnight, then E-SE 5-15 kt in the afternoon. Winds

aloft at 10kft MSL: variable 5-15kt.



KBOI...VFR with clear skies. Surface winds: SE 5-10kt.



&&



.BOI WATCHES/WARNINGS/ADVISORIES...

ID...None.



OR...None.



&&



$$



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SHORT TERM...JM

LONG TERM....JM

AVIATION.....JM