324
FXUS65 KBOI 170346
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
846 PM MST FRI JAN 16 2026
DISCUSSION
STRONGER NORTHERLY FLOW ALOFT THROUGH EASTERN
IDAHO HAS BROUGHT IN COLDER AIR ABOVE OUR EASTERN ZONES,
SLIGHTLY WEAKENING THE INVERSION AND DECREASING THE FOG IN THE
SNAKE BASIN VS LAST NIGHT. SO FAR, STRATUS AND FOG HAVE BEEN
MINIMAL, AND THE DECISION TO NOT ISSUE ANOTHER DENSE FOG
ADVISORY IS PROVING CORRECT. SOME HI-RES MODELS STILL FORM
SHOW FOG OVERNIGHT IN THE LOWER TREASURE VALLEY, BUT LESS
THAN LAST NIGHT. ON SATURDAY, MODELS WEAKEN THE NORTHERLY FLOW,
WITH WARMING ALOFT MAKING THE INVERSION STRONGER AGAIN AND
LIKELY INCREASING FOG IN THE SNAKE BASIN AGAIN SATURDAY NIGHT.
OTHERWISE, PERSISTENCE THROUGH AT LEAST TUESDAY. NO UPDATES.
AVIATION
FOG/LOW STRATUS EXPECTED TO FILL IN SNAKE PLAIN
AGAIN OVERNIGHT AND RETURN IFR-LIFR CONDITIONS. VFR CONDITIONS
IN THE MTNS AND ACROSS SE OREGON. SURFACE WINDS: W-NW 5-10 KT
IN THE SNAKE PLAIN, AND VARIABLE ELSEWHERE OVERNIGHT. WINDS
ALOFT AT 10KFT MSL: N-NW 15-30 KT.
KBOI...FOG/LOW STRATUS AND IFR-VLIFR CONDITIONS EXPECTED TO
RETURN OVERNIGHT AND CONTINUE THROUGH SATURDAY MORNING.
SURFACE WINDS: LIGHT AND VARIABLE OVERNIGHT, BECOMING SE 5-10
KT SATURDAY MORNING.
SUNDAY OUTLOOK...AREAS OF IFR-LIFR IN VALLEY FOG/LOW STRATUS
WITH BREAKS DURING THE AFTERNOONS SAT/SUN, EXCEPT LIKELY
PERSISTING IN SE OREGON (ESPECIALLY KONO). LOCAL MTN VALLEY
FOG THROUGH NIGHTS/MORNINGS, WITH VFR CLEAR SKIES ABOVE VALLEY
FLOORS. LIGHT AND VARIABLE SURFACE WINDS THROUGH SAT/SUN. N-NW
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.
PREV DISCUSSION
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.
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
DISCUSSION...LC
AVIATION.....JY
AIR STAGNATION...ST
SHORT TERM...ST
LONG TERM....CH
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