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FXUS65 KBOI 111649

AFDBOI



Area Forecast Discussion

National Weather Service Boise ID

949 AM MST Thu Dec 11 2025



.DISCUSSION...Today through Friday afternoon...High pressure

over the region will continue through the remainder of the week,

keeping warm and dry conditions over most areas. Temperatures 

are expected to remain on the warmer end today and tomorrow, 

with peak valley temperatures climbing in the mid to upper 50s 

today and in the lower to mid 50s tomorrow. The West-Central ID 

mountains (near McCall) may see up to 20% chance of light rain 

this afternoon. Winds will stay on the weaker end from the 

Southeast/Southwest for most areas, except in the Magic Valley 

where Southwest gusts up to and around 20 mph are likely this 

afternoon. Patchy morning fog possible in sheltered mountain 

valleys Friday morning. Low mixing heights are still expected 

tonight through the weekend, so an air stagnation advisory 

remains intact Friday 12Z through Sunday 12Z. 





&&



.AVIATION...Mainly VFR with high clouds. Patchy fog will 

persist across sheltered valleys of SE Oregon and SW Idaho 

through 19z. Scattered light showers returning to the west-

central Idaho mountains this afternoon, with MVFR/IFR conditions

and mountain obscuration in precipitation. Snow levels 

7500-8500 ft MSL. Surface winds: W-SE 5-15 kt. Winds aloft at 

10kft MSL: W-NW 25-40 kt. 



KBOI...VFR. Surface winds: SE less than 10 kt, becoming NW 4-8 kt 

this afternoon.



Weekend Outlook...Mostly VFR with low confidence in low stratus and 

fog in sheltered valleys each morning. Winds will generally be from 

W-SW less than 10 kt. 





&&



.AIR STAGNATION...A broad upper-level ridge will continue, with

mixing heights lowering to 1,500 to 2,500 feet AGL today and to

1,000 to 2,000 feet AGL Friday through Sunday. At the same 

time, winds are expected to be less than 10 mph resulting in 

sustained poor ventilation. An Air Stagnation Advisory will 

remain in effect Friday through Sunday. A system early next week

may provide increased mixing and winds, ending the air 

stagnation, with an active pattern expected beyond.





&&



.PREV DISCUSSION...

SHORT TERM...Today through Saturday night...Continued warm and 

dry several more days under a broad long wave upper ridge anchored

over the eastern Pacific and western US. The atmospheric river in

the north Pacific has shifted north and now comes inland across

WA and northern ID. A surface inversion, along with light winds,

has created air stagnation in the valleys that will continue 

through at least Sunday night. High temps will continue 15 to 

20 degrees above normal, but not quite as warm as yesterday. 

Low temps should get gradually colder in the valleys as the 

inversion persists, but not as cold as it would be with snow 

cover. We should also have less valley fog than Wednesday 

morning as the air mass continues to slowly dry out.



LONG TERM...Sunday through Thursday...Above normal temperatures 

with clearing skies will continue air stagnation concerns as high 

pressure remains over the Intermountain West through Monday. The 

ridge axis will gradually move east on Sunday, bringing a slight 

reduction in temperatures and an increase in clouds as a weak low 

skirts to our south over southern Nevada. This low will bring a 

slight uptick in westerly winds, but likely won't bring enough 

mixing to clear out any lingering low clouds or stagnant air in 

sheltered valleys. That pattern shift looks to come on Tuesday 

with another atmospheric river. This plume of moisture is poised

to move into the Pacific Northwest on Tuesday, bringing high 

terrain showers primarily in southeast Oregon and central Idaho.

Snow levels will likely remain elevated around 7000-8500 feet 

MSL thanks to warm southwest flow initially, but could lower 

back to 5000-6000 feet MSL by Wednesday. There is slight 

disagreement among long range models in the strength of the 

Pacific High, with some ensemble solutions showing the ridge 

maintaining strength over the region and keeping showers to the 

north and west of southeast Oregon and southwest Idaho Tuesday 

through Thursday.



With some lingering uncertainty in the evolution of the pattern, 

current forecast chances for any significant accumulation of rain 

or snow are minimal over our region. Temperatures look to remain

around 10-20 degrees above normal through the long term period 

with later weekdays showing the best potential for significant 

cooling.



&&



.BOI WATCHES/WARNINGS/ADVISORIES...

ID...Air Stagnation Advisory from 5 AM Friday to 5 AM MST Monday 

     IDZ012-014-016-033.

OR...Air Stagnation Advisory from 5 AM MST /4 AM PST/ Friday to 5 

     AM MST /4 AM PST/ Monday ORZ061>064.



&&



$$



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DISCUSSION...JY

AVIATION.....JDS

AIR STAGNATION...JY

SHORT TERM...LC 

LONG TERM....SA