338
FXUS65 KBOI 202106
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
206 PM MST TUE JAN 20 2026
SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT
FORECAST REMAINS
STRONGLY TIED TO PERSISTENCE, WITH ALL MODEL ELEMENTS AND MOS
VALUES ESSENTIALLY UNCHANGED FROM DAY TO DAY THROUGH THROUGH
THURSDAY NIGHT. WE MERELY CORRECTED THEM TO RECENT OBSERVED
VALUES. THE TOP OF THE VALLEY INVERSION WILL STAY NEAR 4000
FEET MSL IN OREGON, SLOPING TO 4500 FEET MSL IN IDAHO, WITH
CLOUDY, COLD WEATHER AND PATCHY NIGHT/MORNING FOG BELOW THOSE
LEVELS, BUT MOSTLY CLEAR SKIES AND MILD DAYTIME TEMPS ABOVE.
NIGHTS WILL BE COLD, THOUGH, WITH GOOD RADIATIONAL COOLING
UNDER THE MOSTLY CLEAR SKIES. LIGHT WINDS.
LONG TERM...FRIDAY THROUGH TUESDAY
THE BACK END OF A MOSTLY
DRY LONGWAVE TROUGH WILL STEER OUT EAST FRIDAY THROUGH THE
WEEKEND, CONTINUING NORTHWEST FLOW AND DRY CONDITIONS THROUGH
EARLY NEXT WEEK. THE NORTHWEST FLOW WILL BRING COOLER AIR ALOFT,
WHICH MAY HELP MIX OUT VALLEY STRATUS AND FOG. UNCERTAINTY OVER
THIS REMAINS HIGH, AS A LARGE UPPER LEVEL RIDGE WILL BUILD INTO
THE REGION LATE SUNDAY THROUGH TUESDAY. THIS STRONG RIDGING
PATTERN WILL LIKELY RETURN WARM AIR ALOFT AND VALLEY INVERSIONS.
IF THIS PROJECTED PATTERN HOLDS, VALLEYS WOULD AGAIN SEE BELOW
NORMAL TEMPERATURES AND INVERSION STRATUS WHILE MOUNTAINS SEE
ABOVE NORMAL TEMPERATURES THROUGHOUT THE EXTENDED PERIOD. FOR
NOW, AN INVERSION PATTERN REMAINS IN PLACE FOR EARLY NEXT WEEK.
MOST GUIDANCES ALSO SUGGEST THE RIDGE STEERING IN SOME REMNANT
PACIFIC MOISTURE OVER THE CENTRAL MOUNTAINS OF EASTERN OR AND
WESTERN ID, FAVORING SMALL CHANCES OF MOUNTAIN SNOWFALL LATE
MONDAY.
AVIATION
MVFR-IFR BELOW 5K-6K FEET MSL IN THE SNAKE PLAIN
AND SURROUNDING BASINS DUE TO PERSISTENT LOW STRATUS AND FOG.
SURFACE WINDS: W-NW 5-10 KT IN SNAKE PLAIN, BECOMING VARIABLE
UNDER 7 KT LATE AFTERNOON/EVENING. WINDS ALOFT AT 10KFT MSL:
NW-N 15-30 KT.
KBOI...MVFR-IFR LOW STRATUS/FOG TO PERSIST THROUGH AFTERNOON/
EARLY EVENING TODAY. SURFACE WINDS: NW AROUND 5 KT, BECOMING
LIGHT AND VARIABLE AFTER 00Z.
AIR STAGNATION
A STRONG TEMPERATURE INVERSION, ALONG WITH
LIGHT BOUNDARY LAYER WINDS, WILL CONTINUE THE STAGNANT AIR IN
THE VALLEYS OF SOUTHEAST OREGON AND SOUTHWEST IDAHO. MIXING
HEIGHTS WILL REMAIN BELOW 2000 FEET AGL THROUGH AT LEAST
THURSDAY NIGHT, SO THE AIR STAGNATION ADVISORY HAS BEEN EXTENDED
UNTIL 5 AM MST FRIDAY. COOLING ALOFT LATER FRIDAY WILL WEAKEN
THE INVERSION AND MAY PROVIDE TEMPORARY IMPROVEMENT, BUT THE
INVERSION IS EXPECTED TO STRENGTHEN AGAIN THROUGH THE WEEKEND.
BOI WATCHES/WARNINGS/ADVISORIES
ID...AIR STAGNATION ADVISORY UNTIL 5 AM MST FRIDAY
IDZ011>014-016-028-033.
OR...AIR STAGNATION ADVISORY UNTIL 5 AM MST /4 AM PST/ FRIDAY
ORZ061>064.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
SHORT TERM...LC
LONG TERM....JY
AVIATION.....JY
AIR STAGNATION...LC
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