422
FXUS65 KBOI 112104
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
204 PM MST SUN JAN 11 2026
SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT
A STRONG UPPER
LEVEL RIDGE WILL REMAIN IN PLACE AS THE DOMINANT FEATURE OVER
THE INTERMOUNTAIN WEST THROUGH THE PERIOD. THIS FEATURE WILL
KEEP THE STORM TRACK WELL TO OUR NORTH AND PROMOTE DRY
CONDITIONS ACROSS SOUTHEAST OREGON AND SOUTHWEST IDAHO. AS THE
RIDGE STRENGTHENS, VALLEY INVERSIONS WILL DEEPEN AND TRAP COLD
AIR NEAR THE VALLEY FLOORS WHILE TEMPERATURES ALOFT WARM
SIGNIFICANTLY. THIS SETUP WILL RESULT IN A CONTINUATION OF NEAR
NORMAL TEMPERATURES IN THE LOWER VALLEYS, PARTICULARLY THE SNAKE
PLAIN AND BAKER VALLEY, WHILE MOUNTAIN LOCATIONS AND RIDGETOPS
EXPERIENCE UNSEASONABLY WARM CONDITIONS. WITH LIGHT WINDS AND
CLEAR SKIES EXPECTED OVERNIGHT, RADIATIONAL COOLING WILL BE
EFFICIENT. THIS WILL LEAD TO THE DEVELOPMENT OF PATCHY FOG AND
LOW STRATUS IN SHELTERED VALLEYS AND BASINS, INCLUDING THE
TREASURE VALLEY AND LOWER SNAKE PLAIN, BY MONDAY MORNING. ANY
FOG THAT FORMS MAY BE SLOW TO ERODE UNDER THE STRENGTHENING
SUBSIDENCE INVERSION. WINDS WILL REMAIN GENERALLY LIGHT AND
TERRAIN DRIVEN, THOUGH A WEAK SOUTHEASTERLY DRAINAGE WIND MAY
PERSIST IN THE MAGIC VALLEY.
LONG TERM...WEDNESDAY THROUGH SUNDAY
THE FORECAST PERIOD
WILL CONTINUE TO BE DRY UNDER HIGH PRESSURE, WITH CONTINUED AIR
STAGNATION CONCERNS UNDER AN INVERSION. VALLEY COLD POOLS WILL
KEEP LOWER ELEVATION TEMPERATURES LEANING NEAR TO ABOVE NORMAL
(UP TO AROUND 5 DEGREES ABOVE), WHILE HIGHER ELEVATIONS WILL BE
10-15 DEGREES ABOVE NORMAL. HAVE ADJUSTED HIGHER ELEVATION TEMPS
UP TO BETTER CAPTURE THE INVERSION AFFECTS. DAYTIME HIGHS WILL
BE ABOVE FREEZING ACROSS MUCH OF OUR AREA, BARRING THE HIGHEST
PEAKS. ANOTHER IMPLICATION OF THE VALLEY COLD POOL, PAIRED WITH
LIGHT WINDS AND GENERALLY CLEAR SKIES, WILL BE PATCHY FOG EACH
MORNING. THE FAVORED LOCATIONS FOR FOG DEVELOPMENT WILL BE
SHELTERED MOUNTAIN VALLEYS AND LOWER BASINS.
UNCERTAINTY STILL REMAINS COME LATE THURSDAY/FRIDAY. AS HAS BEEN
ADVERTISED, GUIDANCE HAS BEEN IN GOOD AGREEMENT OF A DRY COLD
FRONT/SHORTWAVE CROSSING TO OUR EAST...WITH THE UNCERTAINTY IN THE
WESTWARD EXTENT OF IT. THE GFS HAS BEEN THE MOST AMBITIOUS IN ITS
WESTERN EXTEND, WHICH WOULD BRING INCREASED WINDS AND HELP MIX SOME
OF THE VALLEY INVERSIONS, BUT APPEARS TO BE TRENDING EAST TOWARDS
THE EURO AND EC-AI SOLUTIONS. THE MAJORITY OF THE GRAND ENSEMBLE
MEMBERS STILL FAVOR THAT FARTHER EAST TRACK. EITHER WAY, THE RIDGING
IS EXPECTED TO PERSIST THROUGHOUT THE LONG-TERM WITH NO
PRECIPITATION CHANCES TO BE FOUND. BEYOND THE LONG-TERM PERIOD,
EARLY NEXT WEEK, THERE ARE SOME HINTS THAT WE MAY FINALLY BREAK OUT
OF THIS PATTERN. STAY TUNED!
AVIATION
VFR. AREAS OF FOG/LOW STRATUS WILL REDEVELOP OVERNIGHT,
MOSTLY IN SHELTERED MTN VALLEYS AND LOWER BASINS. MVFR/LIFR IN
FOG/LOW STRATUS WITH MOUNTAIN OBSCURATION. SURFACE WINDS: VARIABLE
UP TO 10KT. WINDS ALOFT AT 10KFT MSL: W-NW 5-25 KT.
KBOI...VFR. SURFACE WINDS: LIGHT AND VARIABLE.
AIR STAGNATION
THE BUILDING HIGH PRESSURE RIDGE WILL MAINTAIN
A STRONG TEMPERATURE INVERSION ACROSS THE REGION THROUGH THE
REMAINDER OF THE WEEK. TRANSPORT WINDS ARE FORECAST TO REMAIN
VERY WEAK, GENERALLY LESS THAN 10 MPH, WITH MIXING HEIGHTS
STRUGGLING TO EXCEED 1500 FEET AGL IN VALLEY LOCATIONS. THESE
CONDITIONS WILL SEVERELY LIMIT ATMOSPHERIC VENTILATION AND LEAD
TO A BUILDUP OF POLLUTANTS NEAR THE SURFACE. THERE IS LOW
CONFIDENCE (20 PERCENT CHANCE) IN THE INVERSION BREAKING LATE
THIS WEEK WITH A WEAK COLD FRONTAL PASSAGE. THE AIR STAGNATION
ADVISORY REMAINS IN EFFECT FOR ALL VALLEY ZONES IN SOUTHEAST
OREGON AND SOUTHWEST IDAHO UNTIL FRIDAY MORNING.
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...JDS
LONG TERM....NF
AVIATION.....NF
AIR STAGNATION...JDS
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page