121
FXUS65 KBOI 162151
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
251 PM MST FRI JAN 16 2026
SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT
HIGH PRESSURE ALOFT
WILL REMAIN CENTERED ALONG THE WEST COAST THROUGH THE SHORT TERM
WITH DRY NORTHERLY FLOW OVERHEAD. THE MAIN STORY WILL CONTINUE
TO BE VALLEY INVERSIONS WITH PERIODS OF FOG AND LOW CLOUDS. FOG
LAST NIGHT ACROSS THE TREASURE AND MAGIC VALLEYS LIFTED TO LOW
STRATUS AS SURFACE WINDS INCREASED. LOW CLOUDS HAVE GRADUALLY
DECREASED IN COVERAGE THIS AFTERNOON, BUT ARE EXPECTED TO
EXPAND ONCE AGAIN OVERNIGHT. AS TEMPERATURES COOL, AREAS OF FOG
WILL REDEVELOP, BUT CONFIDENCE IN DENSE FOG IS LOWER AS LOW
CLOUDS MAY PROVIDE ENOUGH INSULATION TO KEEP CLOUD BASES OFF THE
GROUND (AROUND A 50% CHANCE OF THIS OCCURRING). HOWEVER, WINDS
WILL BE LIGHT OVERNIGHT WHICH FAVORS AT LEAST SOME FOG
DEVELOPMENT.
CONDITIONS OVER THE WEEKEND WILL BE VERY SIMILAR TO TODAY, WITH
FOG AND LOW CLOUDS EACH NIGHT AND MORNING WITH IMPROVEMENT EACH
AFTERNOON. THE TEMPERATURE INVERSION WILL KEEP LOWER VALLEY
TEMPERATURES NEAR OR SLIGHTLY BELOW NORMAL, WHILE THE MOUNTAINS
ABOVE THE INVERSION WILL SEE TEMPERATURES SEVERAL DEGREES ABOVE
NORMAL UNDER MOSTLY CLEAR SKIES.
LONG TERM...MONDAY THROUGH FRIDAY
PERSISTENT UPPER-LEVEL
RIDGING WILL REMAIN OVER THE AREA MONDAY AND TUESDAY. BEGINNING
LATE TUESDAY INTO WEDNESDAY, THE HIGH PRESSURE ALOFT WILL BEGIN
TO WEAKEN, ALLOWING THE PATTERN TO START CHANGING. WEAK UPPER-
LEVEL RIDGING WILL STILL BE IN PLACE WEDNESDAY, INDICATED BY THE
CLUSTERS AND 500 MB HEIGHT CLIMATOLOGY. LARGER IMPACTS FROM
THIS PATTERN CHANGE WILL BEGIN TO ARRIVE MIDDAY THURSDAY INTO
FRIDAY, WHEN A SHORTWAVE TROUGH SYSTEM WILL MOVE NW TO SE, FROM
THE PACIFIC NW TO THE GREAT BASIN REGION. THOUGH A 20-30% CHANCE
OF SHOWERS SHOWS UP IN THE MTNS FOR THUR/FRI, THE DEEPEST
MOISTURE WILL CONTINUE TO BE ROUTED AROUND US (NORTH AND SOUTH)
THROUGH NEXT WEEK (AND LIKELY NEXT WEEKEND). TEMPERATURES WILL
FLIP AS THE INVERSION BREAKS, WARMING ACROSS THE LOWEST
ELEVATIONS, WHILE COOLING IN THE MOUNTAINS.
AVIATION
IFR-LIFR CONDITIONS WILL PERSIST NEAR KONO.
IMPROVEMENT TO VFR-MVFR CONDITIONS IS BEING SEEN FROM KEUL TO
KTWF/KJER AND WILL REMAIN THROUGH AFTERNOON. VFR CONDITIONS IN
THE MTNS AND ACROSS SE OREGON. FOG/LOW STRATUS EXPECTED TO FILL
IN SNAKE PLAIN AGAIN OVERNIGHT CREATING IFR-LIFR CONDITIONS
AGAIN. SURFACE WINDS: E 5-15 KT IN THE SNAKE PLAIN, VARIABLE
ELSEWHERE. WINDS BECOMING LIGHT AND VARIABLE OVERNIGHT AREA-
WIDE. WINDS ALOFT AT 10KFT MSL: N 15-30 KT.
KBOI...MVFR-VFR THROUGH AFTERNOON. FOG/LOW STRATUS AND IFR-
VLIFR CONDITIONS WILL RETURN FRIDAY NIGHT, THOUGH EXPECT A
DELAYED START UNTIL AFTER 03Z, WITH 60% CHANCE BY 05Z. SURFACE
WINDS: SE 9-14, BECOMING LIGHT AND VARIABLE AFTER SUNSET.
WEEKEND OUTLOOK...AREAS OF IFR-LIFR IN VALLEY FOG/CLOUDS WITH
BREAKS DURING THE AFTERNOONS. SOME AREAS OF SE OREGON (INCLUDING
KONO) COULD SEE AN EXTENDED PERIOD OF IFR IN FOG/CLOUDS. LOCAL
MTN VALLEY FOG, WITH VFR ABOVE VALLEY FLOORS. LIGHT SURFACE
WINDS AND N 5-20 KT WINDS AT 10KFT MSL.
AIR STAGNATION
A SYSTEM WELL TO OUR EAST BROUGHT INCREASED
WINDS DRAINING DOWN THE SNAKE BASIN TODAY. WINDS WILL BE LIGHTER
ON SATURDAY, THEN VERY LIGHT SUNDAY INTO EARLY NEXT WEEK AS HIGH
PRESSURE ALOFT REMAINS ENTRENCHED. THIS WILL KEEP THE
TEMPERATURE INVERSION IN PLACE. MIXING HEIGHTS WILL REMAIN
BELOW 2KFT THROUGH EARLY NEXT WEEK, AND THE AIR STAGNATION
ADVISORY HAS BEEN EXTENDED THROUGH TUESDAY AFTERNOON TO REFLECT
THIS. HOWEVER, THERE IS POTENTIAL FOR STAGNANT CONDITIONS TO
PERSIST FOR A COUPLE OF DAYS BEYOND TUESDAY BEFORE A MORE ACTIVE
PATTERN RETURNS.
BOI WATCHES/WARNINGS/ADVISORIES
ID...AIR STAGNATION ADVISORY UNTIL 5 PM MST TUESDAY
IDZ011>014-016-028-033.
OR...AIR STAGNATION ADVISORY UNTIL 5 PM MST /4 PM PST/ TUESDAY
ORZ061>064.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
SHORT TERM...ST
LONG TERM....CH
AVIATION.....CH
AIR STAGNATION...ST
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