598
FXUS65 KBOI 250329
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
829 PM MST WED DEC 24 2025
DISCUSSION
MOIST SOUTHERLY FLOW ALOFT ABOVE A WEAK SURFACE
COLD FRONT WERE PRODUCING RAIN IN MOST OF WESTERN ID THIS
CHRISTMAS EVE, BUT SHOULD DECREASE OVERNIGHT (EXCEPT IN THE
CENTRAL ID MOUNTAINS) AS THE MAIN UPPER TROUGH ALONG THE COAST
MOVES INLAND. THE SURFACE PRESSURE GRADIENT HAS ALSO RELAXED AND
WINDS HAVE SUBSIDED. SCATTERED RAIN SHOWERS WILL CONTINUE
CHRISTMAS DAY, WITH EVEN A SLIGHT CHANCE OF THUNDERSTORMS ON
THE IDAHO SIDE. AFTER RECORD-SETTING WARMTH THE LAST TWO DAYS,
TEMPS WILL LOWER SLIGHTLY CHRISTMAS DAY AND FRIDAY, THEN FASTER
FRIDAY NIGHT AND SATURDAY UNDER NORTHERLY FLOW ALOFT BEHIND THE
EASTWARD-DEPARTING UPPER TROUGH. SNOW LEVEL WILL LOWER ENOUGH
TO PRODUCE SEVERAL INCHES ACCUMULATION IN ID ABOVE 4500 FEET
NORTH OF THE SNAKE BASIN FRIDAY NIGHT. COLDER, DRIER AIR WILL
COME IN SATURDAY AS A NEW UPPER TROUGH COMES IN FROM BC. THE
SOUTH END OF THE ORIGINAL UPPER TROUGH WILL CLOSE OFF A LOW IN
CALIF THAT WILL GO SW-WARD BACK OUT INTO THE SUBTROPICAL PACIFIC
SUNDAY. WHILE THAT LOW IS MOVING SW- WARD AN UPPER RIDGE IN THE
NORTH PACIFIC WILL BE MOVING EASTWARD. THE RIDGE WILL COME
INLAND MONDAY AND OUR HIGHER ELEVATIONS WILL GET WARMER AGAIN,
BUT VALLEYS WILL STAY COLD AND LIKELY FOGGY FOR SEVERAL DAYS,
I.E., INVERSION. LONGEST RANGE MODELS SHOW THE INVERSION ENDING
AROUND NEW YEARS DAY AS A PACIFIC STORM COMES INLAND. CURRENT
FORECAST MATCHES UP WELL WITH LATEST MODELS. NO UPDATES PLANNED
FOR NOW.
AVIATION
WIDESPREAD PRECIPITATION ACROSS E OREGON AND SW IDAHO,
BECOMING SCATTERED OVERNIGHT AND THU. PERIODS OF MVFR-IFR IN
HEAVIER RAIN, IFR-LIFR IN SNOW. MTNS OBSCURED. SNOW LEVELS:
5500-7000FT MSL. AREAS OF FOG/LOW STRATUS OVERNIGHT. SLIGHT
CHANCE OF LIGHTNING OVER WEST-CENTRAL ID AND BOISE MOUNTAINS
THURSDAY. SURFACE WINDS: GENERALLY E-S 5-15 KT OVERNIGHT, THEN
15-25 KT WITH 25-45 KT GUSTS BY LATE THU AM. WINDS ALOFT AT
10KFT MSL: S-SW 30-50 KT OVERNIGHT/THU.
KBOI...GENERALLY VFR. PERIODS OF RAIN, TAPERING OFF BY THURSDAY
SUNRISE. THEN, CONVECTIVE SHOWERS DEVELOPING LATE THU AFTERNOON/
EVE. SLIGHT CHANCE OF LIGHTNING IN SHOWER ACTIVITY. FLIGHT
CATEGORY DEGRADING IN HEAVIER SHOWERS. SURFACE WINDS: SE-E 5-15
KT. GUSTS TO 20-30 KT RETURNING AROUND THU/16Z.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...DEEP MOIST SOUTHERLY
FLOW ON THE EAST SIDE OF AN UPPER LEVEL TROUGH AND STORM SYSTEM
WILL CONTINUE OVER SOUTHWESTERN IDAHO AND SOUTHEASTERN OREGON
TONIGHT THROUGH CHRISTMAS. THE STRONG SURFACE PRESSURE GRADIENT
RESPONSIBLE FOR WINDY CONDITIONS WILL RELAX A BIT TONIGHT AND
WINDS WILL SUBSIDE THIS EVENING. THE MOIST FLOW WILL BRING
INTERMITTENT PERIODS OF RAIN TO THE AREA AS WELL, EVEN IN THE
MOUNTAINS WHERE SNOW LEVELS WILL REMAIN ABOVE 6500 FEET THROUGH
CHRISTMAS. TEMPERATURES WILL COOL A FEW DEGREES IN THE RAIN BUT
WILL STILL BE ABOUT 15 DEGREES ABOVE NORMAL. TEMPERATURES WILL
COOL ANOTHER BY ANOTHER 5 TO 10 DEGREES ON FRIDAY AND SNOW LEVELS
WILL COME DOWN TO THE 4000 TO 5000 FOOT RANGE AS THE MAIN UPPER
LEVEL TROUGH AND STORM SYSTEM MOVE THROUGH THE AREA. THIS WILL
ALLOW FOR SOME ACCUMULATIONS OF SNOW ABOVE THESE ELEVATIONS.
THE BOISE AND WEST CENTRAL MOUNTAINS WILL SEE THE MOST SNOW ON
FRIDAY WITH SNOW EXPECTED ON ROADS AND IN MOUNTAIN COMMUNITIES.
LONG TERM...SATURDAY THROUGH WEDNESDAY...TWAS THE DAY BEFORE
CHRISTMAS, WHEN ALL THROUGH THE OFFICE, NOT A CREATURE WAS
STIRRING... EXCEPT FOR YOUR FRIENDLY NEIGHBORHOOD METEOROLOGISTS
OF COURSE! SATURDAY WILL FEATURE LINGERING PRECIPITATION OVER
THE MOUNTAINS AS AN UPPER LEVEL TROUGH MOVES EAST, DETERIORATING
UPPER LEVEL FORCING AND MOISTURE WILL LEAVE THE LOCAL
OROGRAPHIC FORCING AS THE MAIN DRIVER OF PRECIPITATION. WITH
SNOW LEVELS AT VALLEY FLOORS, SNOW IS LIKELY TO BE THE DOMINANT
PRECIP TYPE. WITH DECREASING MOISTURE IN NORTHWEST FLOW ALOFT,
MINIMAL ADDITIONAL ACCUMULATIONS ARE EXPECTED SATURDAY, WITH UP
TO 1.5 INCHES ACROSS THE HIGHEST PEAKS.
SUNDAY AND BEYOND, CONSENSUS IS HIGH ON A SIGNIFICANT PATTERN
CHANGE. AS THE TROUGH PROPAGATES EAST, IT WILL UNDERGO A WAVE-
BREAK, CLOSING OFF INTO A RETROGRADING LOW OVER THE PACIFIC.
WITH RIDGING BUILDING IN OVER IT, OUR AREA WILL GET PLACED IN
THE DRY REGION OF A REX BLOCK. WITH STRONG SUBSIDENCE UNDER THE
HIGH PRESSURE, LIGHT WINDS, AND A LOW SUN ANGLE, MIXING HEIGHTS
WILL TANK AND GIVE WAY FOR A PROLONGED VALLEY INVERSION. THIS
INVERSION, PAIRED WITH INCREASED SURFACE MOISTURE FROM THE
ACTIVE PATTERN AS OF LATE, MEAN THAT FOG/LOW STRATUS WILL LIKELY
BE IN PLAY THROUGHOUT THE MAJORITY OF THE LONG TERM PERIOD.
THIS SET UP ALSO FAVORS COLD POOLING IN THE VALLEYS, WHICH WOULD
LOWER TEMPERATURES VERSUS WHAT IS CURRENTLY FORECAST, ESPECIALLY
IF IT IS COMBINED WITH REDUCED SOLAR HEATING UNDER A STRATUS
CLOUD DECK. GUIDANCE HAS BEEN TRENDING DOWNWARD WITH THE HIGH
TEMPERATURES, PERHAPS A SIGN THAT THEY ARE STARTING TO PICK UP
ON A COLD POOL? EITHER WAY, HIGH TEMPERATURES MAY STILL BE A
TAD TOO HIGH IN THE LONG TERM, WHILE LOW STRATUS COULD ALSO
KEEP NIGHTTIME TEMPERATURES A FEW DEGREES WARMER THAN THE
CURRENT FORECAST.
BOI WATCHES/WARNINGS/ADVISORIES
ID...NONE.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
DISCUSSION...LC
AVIATION.....SH
SHORT TERM...JB
LONG TERM....NF
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