105
FXUS65 KBOI 140331
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
831 PM MST TUE JAN 13 2026
DISCUSSION
LATEST HRRR GUIDANCE HAS LESS FOG IN THE LOWER
TREASURE VALLEY OVERNIGHT THAN IT DID BEFORE, BUT NAMNEST HIRES
MODEL STILL HAS IT. OVERALL, WE WOULD EXPECT PERSISTENCE TO BE
A GOOD FORECAST FOR SEVERAL MORE DAYS, SO THE REASONS FOR LESS
FOG IN THE HRRR ARE APPARENTLY SUBTLE. WE ALSO NOTE NBM MOS
GUIDANCE HAS BEEN VARYING FROM HOUR TO HOUR, DENSE FOG ONE HOUR,
LIGHT FOG THE NEXT. CURRENT DENSE FOG ADVISORY WILL THEREFORE
BE ALLOWED TO PLAY OUT AS ISSUED. THE AIR STAGNATION ADVISORY
WILL ALSO CONTINUE THROUGH EARLY MONDAY MORNING IN ALL CWA
VALLEYS EXCEPT SOUTH OF THE SNAKE RIVER IN IDAHO, ALTHOUGH IT
NOW LOOKS LIKE THE STAGNATION MIGHT LAST THROUGH WEDNESDAY.
AVIATION
VFR THIS EVENING. MVFR-LIFR CONDITIONS AND MOUNTAIN
OBSCURATION IN AREAS OF FOG/LOW STRATUS EARLY TUESDAY MORNING,
MAINLY IN SHELTERED MOUNTAIN-VALLEYS AND LOWER BASINS. FOG/LOW
STRATUS WILL BEGIN TO DISSIPATE AFTER SUNRISE. SURFACE WINDS:
VARIABLE UP TO 8 KT. WINDS ALOFT AT 10KFT MSL: NW 5-20 KT.
KBOI...VFR THIS EVENING, WITH MIST EXPECTED NEAR THE TERMINAL
AFTER WED/05Z. A 25% CHANCE OF LIFR/VLIFR CONDITIONS WITHIN 5
MILES WITH A 15% CHANCE OF FOG AT THE TERMINAL. CONFIDENCE IS
HIGHER NEAR KEUL, WITH UNCERTAINTY STEMMING FROM HOW FAR UP
VALLEY THE FOG WILL EXTEND. CONDITIONS IMPROVING BY 18Z.
SURFACE WINDS: LIGHT AND VARIABLE.
AIR STAGNATION
THE STRONG RIDGE ALOFT COMBINED WITH LIGHT
SURFACE WINDS WILL CONTINUE TO SUPPRESS VERTICAL MIXING ACROSS
THE REGION. MIXING HEIGHTS ARE EXPECTED TO REMAIN VERY LOW,
GENERALLY BELOW 1000 FEET AGL IN THE VALLEYS, WITH LIGHT
TRANSPORT WINDS. THESE CONDITIONS WILL LEAD TO A BUILDUP OF
POLLUTANTS NEAR THE SURFACE. THE AIR STAGNATION ADVISORY REMAINS
IN EFFECT IN SOUTHEAST OREGON AND MOST OF SOUTHWEST IDAHO
THROUGH THE WEEK. NO SIGNIFICANT PATTERN CHANGE IS EXPECTED
TO SCOUR OUT THE INVERSIONS UNTIL AT LEAST MONDAY, AND POSSIBLY
NOT UNTIL WEDNESDAY.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT...THE UPPER LEVEL
RIDGE WILL REMAIN THE DOMINANT FEATURE OVER THE REGION THROUGH
THE SHORT TERM PERIOD. THIS PATTERN WILL MAINTAIN DRY AND STABLE
CONDITIONS ACROSS SOUTHEAST OREGON AND SOUTHWEST IDAHO. AS THE
RIDGE STRENGTHENS, VALLEY INVERSIONS WILL DEEPEN, TRAPPING COLD
AIR AND POLLUTANTS NEAR THE SURFACE WHILE TEMPERATURES ALOFT
REMAIN UNSEASONABLY WARM. HIGH RESOLUTION MODELS INDICATE A
HIGHER PROBABILITY OF DENSE FOG REDEVELOPING IN THE LOWER
TREASURE VALLEY LATE TONIGHT. DUE TO THIS SIGNAL AND THE
STRENGTHENING INVERSION, A DENSE FOG ADVISORY HAS BEEN ISSUED
FOR THE LOWER TREASURE VALLEY FROM LATE TONIGHT THROUGH
WEDNESDAY MORNING. CONFIDENCE IN DENSE FOG AT BOISE WEDNESDAY
MORNING IS LOWER, WITH AROUND A 30% CHANCE OF OCCURRENCE.
PATCHY FOG IS ALSO EXPECTED IN THE UPPER TREASURE VALLEY,
WESTERN MAGIC VALLEY, AND SHELTERED MOUNTAIN VALLEYS. STRATUS
AND FOG WILL BE DIFFICULT TO DISSIPATE, ESPECIALLY IN THE LOWER
TREASURE AND LONG VALLEYS ON WEDNESDAY. EXPECT FOG TO RETURN
ACROSS MUCH OF THE SNAKE RIVER PLAIN AND SHELTERED VALLEYS
ACROSS SOUTHEAST OREGON AND SOUTHWEST IDAHO WEDNESDAY NIGHT
INTO THURSDAY. TEMPERATURES WILL REMAIN INVERTED, WITH VALLEYS
SEEING HIGHS NEAR OR SLIGHTLY BELOW NORMAL AND MOUNTAIN
LOCATIONS SEEING HIGHS 5 TO 10 DEGREES ABOVE NORMAL. THE NBM,
ALONG WITH MOST GUIDANCE, HAS STRUGGLED TO RESOLVE THE COLD AIR
TRAPPED WITHIN THE INVERSION IN SHELTERED VALLEYS. CONSEQUENTLY,
AREAS TRAPPED IN STRATUS AND FOG WILL SEE VERY LITTLE DIURNAL
TEMPERATURE RANGE.
LONG TERM...FRIDAY THROUGH TUESDAY...CLUSTERS AND ENSEMBLES
CONTINUE TO POINT AT A HIGH AMPLITUDE RIDGE OVER THE WESTERN
U.S., WITH LITTLE RELIEF IN SIGHT. AIR STAGNATION AND FOG WILL
CONTINUE TO BE HEADLINES THROUGH THE EXTENDED. HIGHER ELEVATIONS
WILL CONTINUE TO HAVE WARMER TEMPERATURES THAN LOWER MOUNTAIN
VALLEYS.
RELIEF FROM THE STAGNANT CONDITIONS LOOKS TO COME LATE NEXT
TUESDAY INTO WEDNESDAY WITH AN UPPER LEVEL TROUGH BRINGING
CHANCES OF PRECIPITATION AND INCREASED MIXING. ENSEMBLE MEMBERS
OF THE ECMWF/GFS SHOW VARYING DEGREES OF PRECIPITATION AND
TIMING OF THE NEXT SYSTEM, BUT THERE IS GENERALLY GOOD AGREEMENT
IN THE BREAKDOWN OF THE RIDGE BY THE END OF NEXT WEEK.
BOI WATCHES/WARNINGS/ADVISORIES
ID...AIR STAGNATION ADVISORY UNTIL 5 AM MST MONDAY
IDZ011>014-016-028-033.
DENSE FOG ADVISORY UNTIL NOON MST WEDNESDAY IDZ012.
OR...AIR STAGNATION ADVISORY UNTIL 5 AM MST /4 AM PST/ MONDAY
ORZ061>064.
DENSE FOG ADVISORY UNTIL NOON MST /11 AM PST/ WEDNESDAY ORZ064.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
DISCUSSION...LC
AVIATION.....NF
AIR STAGNATION...JDS/LC
SHORT TERM...JDS
LONG TERM....CH
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