621
FXUS65 KBOI 191645
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
945 AM MST MON JAN 19 2026
DISCUSSION
WIDESPREAD STRATUS DECK REMAINS FIRMLY ENTRENCHED
ACROSS THE LOWER TREASURE VALLEY AND PORTIONS OF THE SNAKE
PLAIN THIS MORNING. PATCHY DENSE FOG REMAINS IN PARTS OF THE
WESTERN MAGIC VALLEY THIS MORNING BUT IS EXPECTED TO LIFT INTO A
LOW STRATUS LAYER EARLY AFTERNOON. HIGH-RES MODELS CONTINUE TO
SUGGEST THAT EROSION OF THE STRATUS WILL OCCUR LATER THIS
AFTERNOON MAINLY EAST AND SOUTH OF MOUNTAIN HOME, THOUGH IT
RETURNS AROUND MIDNIGHT. SHOULD THIS OCCUR, TEMPERATURES WILL BE
ABOUT 5-8 DEGREES WARMER FOLLOWED BY PATCHY DENSE FOG AGAIN FOR
THE WESTERN MAGIC VALLEY. CONFIDENCE IN ANY CLEARING IS LOW
(20% CHANCE), GIVEN MOST OF THE SNAKE RIVER PLAIN IS COVERED BY
STRATUS WITH NO SIGNIFICANT ENOUGH WINDS OR DRYING SEEN TO HELP
CLEAR THE STRATUS. THE CURRENT FORECAST WAS TRENDED TOWARDS
PERSISTENCE OF THE STRATUS SO NO UPDATES NEEDED AT THIS TIME.
AVIATION
MVFR-LIFR BELOW 5KFT MSL IN THE SNAKE PLAIN AND
SURROUNDING BASINS DUR TO PERSISTENT LOW STRATUS AND FOG.
SIMILAR TO PREVIOUS DAYS, A BRIEF SHOT AT CLEARING THIS
AFTERNOON BEFORE REDEVELOPMENT TONIGHT. SURFACE WINDS: VARIABLE
LESS THAN 6 KT. WINDS ALOFT AT 10KFT MSL: N 5-15 KT.
KBOI...MVFR CEILINGS EXPECTED THROUGH THE DAY WITH LOW STRATUS,
BACK DOWN TO IFR-LIFR TONIGHT. SURFACE WINDS: VARIABLE UP TO 6
KT.
AIR STAGNATION
STRONG HIGH PRESSURE ALOFT CONTINUES TO
MAINTAIN A STEEP TEMPERATURE INVERSION ACROSS THE REGION.
SURFACE WINDS ARE EXPECTED TO REMAIN LIGHT, GENERALLY UNDER 10
MPH IN THE VALLEYS, WITH MIXING HEIGHTS STAYING WELL BELOW 1500
FT AGL. THESE CONDITIONS WILL PREVENT THE DISPERSION OF
POLLUTANTS, KEEPING AIR QUALITY STAGNANT IN THE LOWER VALLEYS.
THE AIR STAGNATION ADVISORY REMAINS IN EFFECT THROUGH THURSDAY
MORNING AS LITTLE CHANGE IN THE PATTERN IS EXPECTED.
PREV DISCUSSION
SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT...OVERNIGHT
SATELLITE IMAGERY SHOWING THE INLAND NW BLANKETED IN LOW
CLOUDS/FOG. WEBCAMS AND OBSERVATIONS REVEALING THE DENSE FOG IN
THE WESTERN MAGIC VALLEY IS STARTING TO LIFT INTO A LOW
OVERCAST SO WILL SEE IF TREND HOLDS IN REGARDS TO KEEPING THE
DENSE FOG ADV. HIGH-RES MODELS SHOW A FAIR AMOUNT OF
MIXING/EROSION EAST/SOUTH OF MOUNTAIN HOME-GLENNS FERRY TODAY AS
DRIER AIR WORKS IN ALOFT. FOR NOW HAVE LEANED ON PERSISTENCE
GIVEN THE EXTENTS OF STRATUS IN THE SNAKE PLAIN BUT THERE IS A
CHANCE THAT THESE AREAS BREAK INTO THE SUN. HAVE COUPLED THE
TEMPERATURE FORECAST WITH THE EXPECTED CLOUD COVER SO CERTAINLY
COULD BE WARMER IF THESE AREAS BREAK OUT INTO THE SUN. OTHERWISE
KEPT EXTENSIVE VALLEY CLOUD COVER IN THE FORECAST THROUGH
TUESDAY, WITH SOME IMPROVEMENT STARTING ON WEDNESDAY. BELIEVE
THE CORE OF IT (TREASURE VALLEY) COULD REMAIN INTACT BEYOND
THAT TIME. BY WEDNESDAY MORNING THE LOWER TREASURE VALLEY
(ONTARIO AREA) WOULD BE AT 7 DAYS OF CONTINUOUS LOW CLOUD/FOG
WHICH IF IT HOLDS WOULD BE ONE OF THE LONGER EVENTS ON RECORD
(THE ~12 STRAIGHT DAYS AT THE END OF JANUARY 2014 IS THE
LONGEST OR SECOND LONGEST ON RECORD FOR ONTARIO, CALDWELL AND
BOISE). MOUNTAINS STAY IN THE SUN AND RELATIVELY WARMER
TEMPERATURES THROUGH WED.
LONG TERM...THURSDAY THROUGH MONDAY...THE UPPER RIDGING WILL
GIVE SOME GROUND LATE IN THE WEEK AS A SHORT WAVE TROUGH AND
ACCOMPANYING COLD FRONT SWING THROUGH THE PAC NW. OVERALL THE
MODELS HAVE SHIFTED EAST WITH THE EXTENT OF COLD AIR AND
PRECIPITATION CHANCES LATE IN THE PERIOD (A COMMON THEME THIS
WINTER). FOR NOW IT STILL LOOKS TO GET COLD ENOUGH ALOFT TO AT
LEAST BRIEFLY BREAK THE INVERSION (FRI/SAT) BEFORE THE POTENTIAL
RETURN OF UPPER RIDGING. THE CHANCE FOR SNOW HAS RETRACTED TO
AROUND 20% THROUGH SATURDAY IN THE E-CENTRAL OREGON AND
W-CENTRAL ID MTNS AND NO MORE THAN 30% THROUGH MONDAY. THE SNAKE
PLAIN AND SE OREGON ARE LIKELY TO REMAIN DRY THROUGH THE
WEEKEND, THOUGH WARMER THAN RECENT DAYS.
BOI WATCHES/WARNINGS/ADVISORIES
ID...AIR STAGNATION ADVISORY UNTIL 11 AM MST THURSDAY
IDZ011>014-016-028-033.
DENSE FOG ADVISORY UNTIL 11 AM MST THIS MORNING IDZ016.
OR...AIR STAGNATION ADVISORY UNTIL 11 AM MST /10 AM PST/ THURSDAY
ORZ061>064.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
DISCUSSION...JDS
AVIATION.....JM
AIR STAGNATION...JDS
SHORT TERM...DG
LONG TERM....DG
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