905
FXUS65 KBOI 251007
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
307 AM MST THU DEC 25 2025
SHORT TERM...TODAY THROUGH SATURDAY NIGHT
ISOLATED SHOWERS
WILL CONTINUE THIS MORNING AS A WEAK WARM FRONT PASSES THROUGH
THE REGION. THIS ACTIVITY WILL SHIFT NORTHWARD THROUGH THE
MORNING HOURS, LEADING TO A BRIEF BREAK IN PRECIPITATION FOR THE
LATE MORNING AND EARLY AFTERNOON. HOWEVER, MOISTURE AND
DYNAMICS WILL INCREASE LATER TODAY AS AN UPPER LEVEL JET MAX
SPREADS INLAND ACROSS THE INTERMOUNTAIN WEST. THIS WILL SUPPORT
MORE CONVECTIVELY DRIVEN SHOWERS AND THUNDERSTORMS THIS
AFTERNOON AND EVENING ACROSS MUCH OF THE AREA. MODERATE
RAINFALL, GUSTY WINDS, AND EVEN LIGHTNING WILL BE POSSIBLE WITH
THE STRONGEST SHOWERS. SNOW LEVELS REMAIN UNSEASONABLY HIGH,
STAYING ABOVE 6500 FEET THROUGH CHRISTMAS DAY. TEMPERATURES WILL
COOL SLIGHTLY IN THE RAIN BUT REMAIN ROUGHLY 15 DEGREES ABOVE
NORMAL. THERE IS A 30 PERCENT CHANCE THAT BOISE REACHES 60
DEGREES TODAY, WHICH WOULD TIE THE RECORD SET IN 1885.
ON FRIDAY, TEMPERATURES WILL COOL ANOTHER 5 TO 10 DEGREES AS
THE PRIMARY UPPER LEVEL TROUGH AND COLD FRONT MOVE THROUGH THE
REGION. SNOW LEVELS WILL DROP INTO THE 4000 TO 5000 FOOT RANGE
BY FRIDAY AFTERNOON, BRINGING ACCUMULATIONS TO THE MOUNTAINS AND
MOUNTAIN COMMUNITIES. THE BOISE AND WEST CENTRAL MOUNTAIN
VALLEYS COULD SEE 4 TO 7 INCHES OF SNOW, WITH UP TO 16 INCHES
POSSIBLE AT BANNER SUMMIT THROUGH FRIDAY NIGHT. CONSEQUENTLY, A
WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR THE WEST CENTRAL
MOUNTAINS.
PRECIPITATION WILL BEGIN TO TAPER OFF SATURDAY AS THE TROUGH
SHIFTS EAST. LINGERING MOISTURE AND NORTHWEST FLOW ALOFT WILL
MAINTAIN LIGHT SNOW SHOWERS OVER THE MOUNTAINS, BUT ADDITIONAL
ACCUMULATIONS SHOULD BE MINIMAL. WITH SNOW LEVELS FALLING TO
VALLEY FLOORS, ANY LIGHT PRECIPITATION IN THE LOWER ELEVATIONS
WOULD LIKELY BE SNOW OR A RAIN AND SNOW MIX, THOUGH NO
ACCUMULATION IS EXPECTED. HIGH PRESSURE BEGINS TO BUILD SATURDAY
NIGHT, LEADING TO CLEARING SKIES AND THE POTENTIAL FOR A
PROLONGED VALLEY INVERSION TO DEVELOP. TEMPERATURES WILL
CONTINUE A COOLING TREND, RETURNING CLOSER TO SEASONAL AVERAGES
BY SATURDAY NIGHT.
LONG TERM...SUNDAY THROUGH THURSDAY
SANTA'S SLEIGH HAS PASSED
OVER THE REGION, NO REPORTS YET OF PRESENTS BEING DELIVERED, AN
INDICATOR THAT THE KIDS OF SE OREGON AND SW IDAHO ARE FAST ASLEEP
WITH A 99.9% CHANCE OF BEING ON THE NICE LIST. UNFORTUNATELY, IT
SEEMS LIKE THE PRESENT THAT WAS LEFT AT THE OFFICE WAS A REX BLOCK
NEXT WEEK, WHICH WE DEFINITELY DIDN'T ON THE CHRISTMAS LIST. BUT
THAT'S EXACTLY WHAT THE ATMOSPHERE IS UNWRAPPING AS A RETROGRADING
CUT OFF LOW SUPPORTS HIGH PRESSURE BUILDING OVER THE AREA. THIS HIGH
PRESSURE WILL PUSH THE STORM TRACK NORTH IN A TEXTBOOK REX BLOCK. ON
THE SURFACE, THIS WILL MEAN QUICKLY DEVELOPING INVERSIONS UNDER
SUBSIDENCE WITH MIXING HEIGHTS MOST OF THE WEEK AROUND 800-1000 FT
AGL. SOME MODELS SHOW A SLOW START TO THE INVERSION WITH MIXING
HEIGHTS AT 2000 FT AGL, BUT EVEN THIS WOULD SUPPORT STAGNANT
CONDITIONS, REGARDLESS OF THE FACT THAT MODELS MIGHT BE TOO SLOW IN
BUILDING THE INVERSION. FOG/LOW STRATUS IS LIKELY EACH DAY, WITH WET
SOILS FROM RECENT RAINS AND COLDER TEMPERATURES THAN WE'VE SEEN
RECENTLY (THOUGH STILL NEAR TO JUST ABOVE NORMAL IN THE FORECAST).
TEMPS CONTINUE TO TREND DOWN EACH FORECAST RUN AS MODELS RESOLVE THE
INVERSION BETTER. MODEL CONSENSUS IS HIGH IN A BREAKDOWN OF THE
RIDGE AND INVERSION LATER NEXT WEEK.
AVIATION
ISOLATED PRECIP CONTINUES IN SE OR AND SW
ID THROUGH FRIDAY MORNING WITH SNOW LEVELS 5-7 KFT MSL. FOG/LOW
STRATUS THIS MORNING IN SHELTERED VALLEYS CAUSING LOCAL IFR-LIFR.
PRECIP COVERAGE INCREASES THIS AFTERNOON AND BECOMES MORE SHOWERY
WITH BRIEF LIGHT TO MODERATE RAINFALL FOR VALLEYS AND MIXED/SNOW FOR
MOUNTAINS. FOG/LOW STRATUS REDEVELOPMENT IS POSSIBLE FRIDAY MORNING.
SURFACE WINDS: S-SE 5-15 KT THIS MORNING INCREASING TO 10-20 KT WITH
GUSTS TO 25-35 KT THIS AFTERNOON. WINDS ALOFT AT 10 KFT MSL: S-SW 30-
60 KT.
KBOI...VFR LIKELY THROUGH THE MORNING, BUT WITH A 15% CHANCE OF IFR-
LIFR FOG/STRATUS NEAR OR AT THE TERMINAL. THIS AFTERNOON BRIEF LIGHT
TO MODERATE RAIN SHOWERS MAY DEVELOP IN THE AREA BEFORE ANOTHER 20%
CHANCE OF FOG/STRATUS FRIDAY MORNING. SURFACE WINDS: SE 8-12 KT.
WEEKEND OUTLOOK...PERSISTENT SNOW SHOWERS IN HIGH TERRAIN FRI THRU
SAT AFTERNOON, WITH IFR-LIFR CONDITIONS IN SNOW. SNOW LEVELS 3-4 KFT
MSL DROP TO VALLEY FLOORS SAT MORNING. SCATTERED PRECIPITATION IN
LOWER ELEVATIONS DURING THIS TIME. PRECIP CLEARS BY SAT NIGHT AS SUN
IS DRIER, BUT WITH POSSIBLE FOG/STRATUS THAT MORNING AS AN INVERSION
BUILDS. SURFACE WINDS: SE-SE 15-20 KT WITH GUSTS TO 30 KT ON RIDGES
FRI, BECOMING W 15-25 KT SATURDAY, AND FINALLY LIGHT AND VARIABLE
SUNDAY.
AIR STAGNATION
HIGH PRESSURE IS FORECAST TO BUILD OVER THE
REGION BEGINNING SATURDAY NIGHT AND WILL STRENGTHEN THROUGH THE
EARLY PART OF NEXT WEEK. THIS PATTERN WILL FAVOR THE DEVELOPMENT
OF A STRONG AND PERSISTENT SURFACE BASED TEMPERATURE INVERSION
FROM SUNDAY THROUGH AT LEAST NEXT TUESDAY. WITH LIGHT WINDS AND
LOW MIXING HEIGHTS (1000-2000 FEET) EXPECTED UNDER THE RIDGE,
THERE IS INCREASING CONCERN FOR DETERIORATING AIR QUALITY AND
POOR VENTILATION IN THE SHELTERED VALLEYS OF SOUTHEAST OREGON
AND SOUTHWEST IDAHO. WHILE IT MAY BE TOO EARLY FOR A FORMAL
ADVISORY, CONDITIONS WILL BE MONITORED CLOSELY AS THE STAGNANT
AIR MASS BECOMES ESTABLISHED.
BOI WATCHES/WARNINGS/ADVISORIES
ID...WINTER WEATHER ADVISORY FROM 5 AM FRIDAY TO 5 AM MST SATURDAY
IDZ011.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
SHORT TERM...JDS
LONG TERM....JM
AVIATION.....JM
AIR STAGNATION...JDS
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