928
FXUS65 KBOI 260958
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
258 AM MST FRI DEC 26 2025
SHORT TERM...TODAY THROUGH SUNDAY NIGHT
AN UPPER LEVEL
TROUGH ALONG THE WEST COAST THIS MORNING WILL PUSH INLAND TODAY,
MOVING ACROSS THE NORTHERN ROCKIES TONIGHT. THIS WILL BRING
PERIODS OF MODERATE SNOWFALL TO THE CENTRAL IDAHO MOUNTAINS.
ISOLATED SHOWERS CONTINUE ACROSS THE REGION AND WILL EXPAND IN
COVERAGE, PARTICULARLY ACROSS SOUTHEAST OREGON AND THE CENTRAL
IDAHO MOUNTAINS, AFTER SUNRISE AS AN EMBEDDED UPPER LEVEL
SHORTWAVE TRAVERSES THE PACIFIC NORTHWEST. SNOW LEVELS AROUND
5000 FEET THIS MORNING SHOULD BE LOW ENOUGH FOR WET ACCUMULATING
SNOW IN THE MOUNTAINS AS TEMPERATURES HOVER NEAR FREEZING
THROUGH EARLY AFTERNOON. THIS WILL LARGELY LIMIT ACCUMULATIONS
BELOW 5500 FEET THIS MORNING, WITH THE HIGHER MOUNTAIN VALLEYS
SEEING UP TO 4 INCHES OF SNOW.
THE NEXT PUSH OF PRECIPITATION ARRIVES LATER THIS EVENING AHEAD
OF A COLD FRONTAL PASSAGE EXPECTED SATURDAY MORNING. THIS WILL
SUPPORT MORE ACCUMULATING SNOW IN THE MOUNTAINS, PARTICULARLY IN
THE WEST CENTRAL AND BOISE MOUNTAINS WHERE A WINTER WEATHER
ADVISORY REMAINS IN EFFECT. EXPECT AN ADDITIONAL 2 TO 5 INCHES
OF SNOW IN THE MOUNTAIN VALLEYS. LOWER VALLEYS CAN EXPECT RAIN
SHOWERS MIXING WITH OR CHANGING TO WET SNOW EARLY SATURDAY
MORNING, THOUGH LITTLE TO NO ACCUMULATION IS EXPECTED ON VALLEY
FLOORS. IN THE MOUNTAINS, SNOW ACCUMULATING ON ROAD SURFACES
WILL CREATE DIFFICULT TRAVEL CONDITIONS. GUSTY WINDS WILL
ACCOMPANY THE FRONTAL PASSAGE, PARTICULARLY OVER EXPOSED
TERRAIN, THROUGH SATURDAY. HOWEVER, BLOWING OR DRIFTING SNOW
APPEARS UNLIKELY AS THE COLDER AIR WILL NOT REACH THE AREA
UNTIL WELL AFTER THE SNOW HAS ENDED.
SATURDAY WILL SEE LINGERING LIGHT SNOW SHOWERS OVER THE
MOUNTAINS UNDER NORTHWEST FLOW ALOFT, WHILE VALLEY PRECIPITATION
CHANCES DECREASE SIGNIFICANTLY. BREEZY CONDITIONS WILL CONTINUE
THROUGH SATURDAY EVENING ACROSS THE AREA WITH GUSTS UP TO 40 MPH,
THOUGH SPEEDS SHOULD REMAIN WELL BELOW ADVISORY CRITERIA. BY
SATURDAY NIGHT AND SUNDAY, AN UPPER LEVEL RIDGE WILL BEGIN TO
BUILD OVER THE INTERMOUNTAIN WEST. THIS WILL STABILIZE THE
ATMOSPHERE, LEADING TO DRY CONDITIONS BUT INCREASING THE
POTENTIAL FOR VALLEY FOG AND LOW STRATUS AS INVERSIONS
STRENGTHEN. TEMPERATURES WILL TREND COOLER, RETURNING TO NEAR
SEASONAL NORMALS BY SUNDAY.
LONG TERM...MONDAY THROUGH FRIDAY
STRONG HIGH PRESSURE WILL
DOMINATE THE WEATHER PATTERN THROUGH MUCH OF THE LONG TERM
PERIOD. THIS SETUP WILL FOSTER THE DEVELOPMENT OF STRONG VALLEY
INVERSIONS, LIKELY RESULTING IN AREAS OF PERSISTENT FOG AND LOW
STRATUS IN THE SHELTERED VALLEYS OF SOUTHWEST IDAHO AND
SOUTHEAST OREGON. UNDER THIS REGIME, VALLEY TEMPERATURES WILL
REMAIN SUPPRESSED WITH LIMITED MIXING, WHILE HIGHER ELEVATIONS
EXPERIENCE MILDER, SUNNY CONDITIONS. THIS PATTERN RAISES
CONCERNS FOR AIR STAGNATION AND DETERIORATING AIR QUALITY IN
VALLEY LOCATIONS THROUGH AT LEAST WEDNESDAY. VALLEY TEMPERATURES
WILL BE DIFFICULT TO FORECAST, WITH LITTLE DIURNAL VARIATION
EXPECTED SHOULD STRATUS OR FOG DEVELOP.
MODELS SHOW DIVERGENCE REGARDING THE BREAKDOWN OF THE RIDGE LATE
IN THE WEEK. SOME GUIDANCE SUGGESTS A TROUGH MAY BRUSH THE
REGION BY THURSDAY OR FRIDAY, POTENTIALLY WEAKENING THE
INVERSION AND INTRODUCING A CHANCE OF PRECIPITATION. HOWEVER,
OTHER CLUSTERS MAINTAIN THE RIDGE, KEEPING THE AREA DRY AND
STABLE. GIVEN THE UNCERTAINTY, THE FORECAST REFLECTS A GRADUAL
TREND TOWARD CLIMATOLOGICAL NORMALS WITH SLIGHT CHANCES FOR
PRECIPITATION RETURNING TOWARDS THE END OF THE PERIOD.
AVIATION
SCATTERED SHOWERS OVERNIGHT INTO FRIDAY AFTERNOON,
INCREASING COVERAGE FRI NIGHT. ISOLATED LIGHTNING. MVFR-LIFR
CONDITIONS IN PRECIP/LOW CLOUDS. SNOW LEVELS: 4.5K-6.5K FT MSL
THIS MORNING, LOWERING TO 3.5K-4.5K FT MSL BY MID-DAY FRI. MTNS
OBSCURED. POTENTIAL FOR LLWS THIS MORNING. SURFACE WINDS: SW-S
15-25 KT WITH 25-45 KT GUSTS. WINDS ALOFT AT 10KFT MSL: SW 35-55
KT.
KBOI...VFR. INTERMITTENT RAIN SHOWERS THROUGH MID-MORNING FRI,
THEN DRY. POTENTIAL FOR LOW-LEVEL WIND SHEAR THIS MORNING.
SURFACE WINDS: SE- SW 5-15 KT. OCCASIONAL GUSTS TO 20-25 KT
THROUGH FRI AFTERNOON.
WEEKEND OUTLOOK...SNOW LEVELS LOWERING TO VALLEY FLOORS
SATURDAY. SCATTERED TO NUMEROUS SNOW SHOWERS SATURDAY, WITH
MVFR-LIFR CONDITIONS IN PRECIP. MTNS OBSCURED. SHOWERS ENDING
SATURDAY EVENING. VFR, COLD, DRY SUNDAY. SURFACE WINDS: W TO
NW 15-25 KT SATURDAY WITH 25-35 KT GUSTS. LIGHT WINDS SUNDAY.
AIR STAGNATION
HIGH PRESSURE IS STILL FORECAST TO BUILD OVER
THE REGION BEGINNING SATURDAY NIGHT AND WILL STRENGTHEN THROUGH
THE EARLY PART OF NEXT WEEK. THIS PATTERN FAVORS 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 UNTIL 5 AM MST SATURDAY IDZ011-013.
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....JDS
AVIATION.....JDS
AIR STAGNATION...JDS
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