460
FXUS65 KBOI 251635
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
935 AM MST THU DEC 25 2025
DISCUSSION
RADAR IS BEGINNING TO LOOK RATHER QUIET THIS
MORNING WITH A BRIEF LULL IN PRECIPITATION. HOWEVER, UPPER LEVEL
DYNAMICS AND MOISTURE WILL INCREASE AS A JET MAX AND SURFACE
COLD FRONT ENCROACH UPON THE AREA. LOOKING UPSTREAM THIS
MORNING, THIS SYSTEM PERFORMED QUITE WELL OVER CALIFORNIA WITH
NUMEROUS LIGHTNING FLASHES OBSERVED. INCREASING INSTABILITY AND
STEEPING LAPSE RATES WILL SUPPORT MORE CONVECTIVE NATURED
SHOWERS THIS AFTERNOON, WITH LOCALLY ENHANCED PRECIP, GUSTY
WINDS, AND LIGHTNING IN PLAY. INSTABILITY LOOKS TO BE RATHER
WEAK WHEN COMPARED TO THE SHEAR THAT WILL OVERSPREAD OUR AREA
(50-60+ KNOTS). WHILE THAT RATIO OF SHEAR TO CAPE MAY HINDER
SUSTAINED UPDRAFT DEVELOPMENT, THE HAZARDS ABOVE WILL STILL BE
AT PLAY. THIS THREAT CONTINUE FRIDAY MORNING IN THE WEST CENTRAL
AND BOISE MOUNTAIN ZONES, AS INSTABILITY HANGS ON A LITTLE BIT
LONGER AND A SECOND FRONTAL PASSAGE CROSSES OVER THE AREA.
TEMPERATURES REMAIN ON TRACK TO BE WITHIN THE RANKS OF THE
WARMEST CHRISTMASES ON RECORD. WITH HIGHS IN THE SNAKE RIVER
PLANE FORECAST TO BE IN THE MID-55S, AND MOUNTAIN VALLEYS
FORECASTED TO BE IN THE 40S. TEMPERATURE TOMORROW COOL BEHIND
THE COLD FRONT. CURRENT FORECAST LOOKS TO BE ON TRACK, WILL
EVALUATE ADDING THUNDER INTO THE WEST CENTRAL/BOISE MOUNTAIN
ZONES IN THE AFTERNOON PACKAGE.
.AVIATION..MOSTLY VFR. SCATTERED RAIN/SNOW SHOWERS TODAY THROUGH
TOMORROW AM BRINGING PERIODS OF MVFR/IFR CONDITIONS. SNOW LEVELS: 5K-
7KFT MSL DROPPING TO 3K-6KFT MSL OVERNIGHT. AREAS OF FOG/LOW STRATUS
IN SHELTERED VALLEYS OVERNIGHT. LOW CONFIDENCE IN LIGHTNING (20%
CHANCE) AND GUSTY OUTFLOW WINDS UP TO 40 KT, PRIMARILY OVER HIGH
TERRAIN IN BOISE MTNS. MTNS OBSCURED. SURFACE WINDS: SE-SW 15-25 KT
WITH 25-45 KT GUSTS. STRONGEST GUSTS UP TO 55 KT WILL BE NEAR THE NV
BORDER. WINDS ALOFT AT 10KFT MSL: SW 35-60 KT.
KBOI...GENERALLY VFR. BRIEF MVFR/IFR CONDITIONS IN CONVECTIVE
SHOWERS DEVELOPING LATE THIS AFTERNOON/EVENING. LOW CONFIDENCE IN
LIGHTNING AND GUSTY OUTFLOW WINDS UP TO 40 KT (20% CHANCE) WITH
STRONGER SHOWERS THIS EVENING. SURFACE WINDS: SE-E 5-15 KT. GUSTS TO
20-30 KT BY LATE MORNING.
WEEKEND OUTLOOK...WIDESPREAD 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 SHOWERS IN LOWER
ELEVATIONS DURING THIS TIME. PRECIP CLEARS BY SAT NIGHT WITH PATCHY
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.
PREV DISCUSSION
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.
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
DISCUSSION...NF
AVIATION.....SA
AIR STAGNATION...JDS
SHORT TERM...JDS
LONG TERM....JM
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