933
FXUS65 KBOI 042204
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
304 PM MST THU DEC 4 2025
SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT
AN ATMOSPHERIC
RIVER IN THE PACIFIC IS STREAMING A RELATIVELY WARM MOISTURE
PLUME UP AROUND A PACIFIC HIGH, AND INTO OUR AREA FROM THE NW.
THE FLOW ALOFT STEADILY INCREASES THROUGH THE SHORT TERM,
MIXING THE WARM AIR DOWN TO THE SURFACE BY FRIDAY AND MIXING
STRONG WINDS AND GUSTS DOWN TO THE SURFACE FRIDAY NIGHT. THERE
WILL BE TWO MAJOR POCKETS OF MOISTURE THAT IMPACT THE AREA, THE
FIRST IS OCCURRING NOW THROUGH FRIDAY MORNING, AND THE SECOND
WARMER, BUT MORE MOIST WILL MOVE THROUGH FRIDAY AFTERNOON
THROUGH FRIDAY NIGHT.
THE FIRST ROUND OF MOISTURE OCCURRING THIS EVENING WILL FEATURE
AN INCREASE IN PW UP TO THE 85TH TO 90TH PERCENTILE, AND THE
REPLACING OF THE COLD AIRMASS WITH THE WARMER AR AIRMASS TONIGHT
THROUGH FRIDAY MORNING. AS WITH MOST ARS THE PRECIPITATION WILL
BE CLOSELY TIED TO TERRAIN DUE TO OROGRAPHY. RAINFALL/LIQUID
EQUIVALENT DURING THIS TIME WILL BE UP TO 0.2" IN LOWER
ELEVATIONS AND UP TO 0.4" IN HIGHER ELEVATIONS. WITH SNOW LEVELS
AT 3-5 KFT MSL, SNOWFALL WILL BE LIMITED TO THE MOUNTAINS AND
HIGHLANDS, WHICH COULD SEE 1-4 INCHES. ADDITIONALLY, THE TIMING
OF THE WARMER AIRMASS MOVING INTO SE OREGON OVERNIGHT MEANS A
LOCALIZED FREEZING/ICY PRECIPITATION THREAT WILL BE PRESENT,
ESPECIALLY THIS EVENING THROUGH MIDNIGHT.
PRECIPITATION WEAKENS BRIEFLY BUT CONTINUES FRIDAY MORNING,
BEFORE THE SECOND ROUND ARRIVES THAT AFTERNOON THROUGH THE
EVENING. WHILE WE ARE NOW WITHIN THE WARMER AIRMASS, PWS RISE TO
NEAR THE 95TH PERCENTILE FOR THIS TIME OF YEAR. RAINFALL/LIQUID
EQUIVALENTS ARE HIGHER, WITH 0.1-0.4" IN LOWER ELEVATIONS AND
0.4-0.8" IN HIGHER ELEVATIONS. WITH SNOW LEVELS NOW AT 5-7 KFT
MSL, INCREASING TO THE SW, SNOW TOTALS RISE BUT ARE LIMITED TO
HIGH MOUNTAIN TOWNS, PASSES, AND RIDGES. AN EXTRA 2-6" OF SNOW
ARE POSSIBLE AROUND 5-6 KFT, BUT UP TO 9" ABOVE 6 KFT.
BOTH ROUNDS OF PRECIPITATION OCCUR IN A 30 HOUR WINDOW, AND
GIVEN THE VERY MOIST SYSTEM WITH IMPACTS TO TRAVEL IN AND OUT OF
MOUNTAIN TOWNS A WINTER WEATHER ADVISORY HAS BEEN ISSUED. STORM
TOTAL RAINFALL/LIQUID EQUIVALENT IS 0.1-0.5" IN LOWER
ELEVATIONS, AND 0.6-1.2" IN HIGHER ELEVATIONS. SIMILARLY
SNOWFALL BELOW 4 KFT MSL WILL BE LESS THAN AN INCH TO FLURRIES
WITH MIXED PRECIP. ABOVE 4KFT TO 6KFT STORM TOTAL SNOW OF 4-7"
IS EXPECTED, AND ABOVE 6KFT IT COULD BE AS HIGH AS 8-12". BEHIND
THE MOISTURE, WIND GUSTS SATURDAY MORNING THROUGH THE DAY REMAIN
25-35 MPH. WINDS HIGHEST IN SE OREGON, SW IDAHO HIGHLANDS, AND
RIDGETOPS. THE WEISER BASIN AND TREASURE VALLEY MAY END UP BEING
JUST SHELTERED ENOUGH FROM THE WIND TO SEE TOO MANY IMPACTS.
LONG TERM...SUNDAY THROUGH THURSDAY
A STRONG UPPER-LEVEL JET WILL
RIDE OVERTOP A STRONG UPPER-LEVEL RIDGE, EXISTING IN THE EASTERN
PACIFIC, AND INTO THE PACIFIC NORTHWEST. PACIFIC MOISTURE AND
EMBEDDED UPPER-LEVEL SHORTWAVE DISTURBANCES AMID THE NORTHWESTERLY
FLOW WILL BRING PERIODIC RAIN AND MOUNTAIN SNOW. OUR AREA WILL BE ON
THE EDGE OF THE STORM TRACK FOR MUCH OF THE PERIOD, AND A STRONG
TEMPERATURE GRADIENT WILL EXIST OVER THE AREA. THIS INCREASES
UNCERTAINTY IN PRECIPITATION AMOUNTS AND TEMPERATURES. HOWEVER,
OVERALL THE PATTERN STRONGLY LEANS MILD AND WET WITH TEMPERATURES
WELL ABOVE NORMAL AND PERIODIC CHANCES OF PRECIPITATION.
A DISTURBANCE AFTERNOON INTO EVENING SUNDAY WILL BRING A 20-50%
CHANCE OF VALLEY RAIN AND A 50-80% CHANCE OF MOUNTAIN RAIN AND SNOW.
SNOW LEVELS WILL BE AROUND 4000-6000 FEET, LOWEST IN THE MORNING
ACROSS THE NORTH. PRECIPITATION AMOUNTS SHOULD BE LIGHT TO MODERATE.
PRECIPITATION CHANCES WILL DIP BRIEFLY ON MONDAY WITH THE UPPER-
LEVEL RIDGE AXIS BUILDING OVERHEAD BEFORE INCREASING ONCE AGAIN
TUESDAY AND WEDNESDAY AS AN ATMOSPHERIC RIVER MOVES INTO THE PACIFIC
NORTHWEST. OUR AREA WILL BE ON THE SOUTHERN EDGE OF THE MOISTURE,
RESULTING IN SOME UNCERTAINTY IN PRECIPITATION AMOUNTS. HOWEVER,
MODERATE PRECIPITATION TOTALS ARE POSSIBLE, ESPECIALLY IN THE
MOUNTAINS, AND THE AIR MASS IS EXPECTED TO BE VERY MILD WITH SNOW
LEVELS PUSHING UP TO 6500-8000 FEET. BY WEDNESDAY, HIGH TEMPERATURES
ARE FORECAST TO REACH 15-20 DEGREES ABOVE NORMAL. STRONG
WESTERLY/NORTHWESTERLY FLOW WILL ALSO BRING BREEZY TO WINDY
CONDITIONS. FORECAST CONFIDENCE IS LOWER ON THURSDAY, BUT STRONG,
MOIST WESTERLY/NORTHWESTERLY FLOW WILL PERSIST ACROSS THE PACIFIC
NORTHWEST. CURRENTLY THIS FORECAST PATTERN LOOKS TO EXIST BEYOND THE
EXTENDED AS WELL.
AVIATION
VFR. CLOUDS INCREASING TODAY AND GRADUALLY LOWERING,
WITH WIDESPREAD RAIN/SNOW ARRIVING FROM THE NORTHWEST THIS AFTERNOON
AND EVENING. MVFR/IFR IN RAIN AND IFR/LIFR IN SNOW. SNOW LEVELS 2.5-
3.5 KFT MSL TODAY, RISING TO 3-5 KFT MSL ACROSS SW ID AND 7-8 KFT
MSL ACROSS SE OR LATE TONIGHT. MOUNTAINS BECOMING OBSCURED. SURFACE
WINDS: LIGHT AND VARIABLE BELOW 10 KTS, EXCEPT KTWF/KJER GUSTING
NEAR 25 KTS OVERNIGHT. AREAS OF LOW-LEVEL WIND SHEAR DEVELOPING
TONIGHT. WINDS AT 10 KFT MSL: NW 20-30 KT, INCREASING TO 35-55 KT
AFTER FRI/00Z.
KBOI...VFR THROUGH MID-AFTERNOON TODAY. INCREASING CLOUDS WITH
LOWERING CEILINGS LATER THIS AFTERNOON, THEN RAIN DEVELOPING AROUND
22-01Z LATE THIS AFTERNOON AND CONTINUING TONIGHT. AROUND A 10%
CHANCE OF RAIN MIXING WITH SNOW TO START, BECOMING PREDOMINANTLY
RAIN LATER TONIGHT. MVFR/IFR CONDITIONS IN PRECIPITATION. SURFACE
WINDS: VARIABLE AROUND 5 KT OR LESS.
WEEKEND OUTLOOK...WIDESPREAD RAIN AND SNOW ON FRIDAY WITH SNOW
LEVELS 6-8 KFT MSL, EXCEPT 4.5-6 KFT ACROSS CENTRAL IDAHO. LIGHTER
PRECIPITATION IS EXPECTED SATURDAY AND SUNDAY WITH SNOW LEVELS 4-6
KFT MSL. MVFR TO LIFR CONDITIONS IN PRECIPITATION WITH MOUNTAINS
OBSCURED. SURFACE WINDS SW-NW 5-15 KT, EXCEPT 15-20 KT WITH GUSTS 25-
40 KT LATE FRIDAY INTO SATURDAY ACROSS HIGHER TERRAIN.
BOI WATCHES/WARNINGS/ADVISORIES
ID...WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 11 PM MST
FRIDAY IDZ011-013.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
SHORT TERM...JM
LONG TERM....CH
AVIATION.....CH
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