834
FXUS65 KBOI 150355
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
855 PM MST SUN DEC 14 2025
DISCUSSION
MOSTLY CLEAR SKIES TONIGHT SHOULD ALLOW
TEMPERATURES TO REACH OR FALL BELOW FREEZING IN MOST PLACES. THE
UPPER-LEVEL RIDGE WILL CONTINUE TO WEAKEN OVERNIGHT AS THE NEXT
SYSTEM MOVES INLAND ACROSS THE PACIFIC NORTHWEST. A WEAK
ASSOCIATED COLD FRONT WILL PUSH EAST LATE MONDAY MORNING,
BRINGING LIGHT, ISOLATED SHOWERS. PRECIPITATION AMOUNTS ARE
EXPECTED TO BE MINIMAL, WITH ONLY A FEW HUNDREDTHS OF AN INCH OF
RAINFALL FORECAST, MAINLY BELOW 4,500 FEET ACROSS BAKER COUNTY
AND INTO THE CENTRAL IDAHO MOUNTAINS. POCKETS OF COLD AIR
TRAPPED IN THE LOWER VALLEYS OF EASTERN OREGON AND FAR WESTERN
IDAHO LATE MONDAY MORNING WILL CREATE A SLIGHT CHANCE OF
FREEZING RAIN SHOULD PRECIPITATION REACH THE SURFACE. SNOW
LEVELS WILL QUICKLY RISE, HOWEVER, TO 7,000 TO 9,000 FEET BY
MONDAY AFTERNOON. BECAUSE THIS FRONTAL SYSTEM DOES NOT APPEAR
STRONG ENOUGH TO FULLY CLEAR THE VALLEY INVERSION, THE AIR
STAGNATION ADVISORY WILL CONTINUE THROUGH TUESDAY MORNING.
A MUCH STRONGER, MORE MOIST SYSTEM REMAINS ON TRACK FOR LATE
TUESDAY INTO WEDNESDAY, WHICH WILL BRING BREEZY CONDITIONS AND
WIDESPREAD PRECIPITATION FAVORING THE CENTRAL IDAHO MOUNTAINS.
DUE TO PERSISTENTLY HIGH SNOW LEVELS (ABOVE 7,000 FEET FOR MOST
OF THE EVENT), AREAS BELOW 7,000 FEET ARE LIKELY TO SEE MODERATE
RAINFALL, TOTALING 0.50 TO 1.00 INCH. STRONG WESTERLY FLOW ALOFT
WILL CREATE A RAIN-SHADOWING EFFECT ON THE TREASURE VALLEY,
LIMITING TOTAL PRECIPITATION TO AROUND 0.10 INCHES. THERE IS
STRONG POTENTIAL FOR WIND HEADLINES ON TUESDAY, ESPECIALLY SOUTH
OF THE SNAKE RIVER PLAIN, WHERE GUIDANCE OVER THE PAST 48 HOURS
CONTINUES TO SHOW ADVISORY-LEVEL WINDS (GUSTS OF 45 TO 57 MPH).
THE FORECAST REMAINS ON TRACK, AND NO SIGNIFICANT UPDATES ARE
NEEDED AT THIS TIME.
AVIATION
MVFR-LIFR CONDITIONS IN PATCHY VALLEY FOG/STRATUS
TONIGHT INTO MONDAY MORNING, MAINLY BETWEEN KONO-KEUL. CLOUDS
INCREASE AS PRECIPITATION MOVES WEST-TO-EAST IN SE OR STARTING MON
MORNING AND IN SW ID MON AFTERNOON. SNOW LEVELS 4-6 KFT MSL RISE TO
7-9 KFT MSL MONDAY EVENING. 15-30% CHANCE OF FREEZING RAIN ACROSS
VALLEYS MON 12-18Z. SURFACE WINDS: LIGHT/VARIABLE. WINDS ALOFT AT
10KFT MSL: W-SW 15-25 KT.
KBOI...VFR. CLOUDS INCREASE WITH A SLIGHT CHANCE OF RAIN BEGINNING
MONDAY AFTERNOON. SURFACE WINDS BECOMING SOUTHEAST TONIGHT, BUT
GENERALLY LIGHT AND VARIABLE.
AIR STAGNATION
A SYSTEM WILL MOVE ACROSS THE AREA ON MONDAY,
WEAKENING THE RIDGE THAT HAS BEEN IN PLACE AND BRINGING LIGHT
PRECIPITATION TO THE AREA. HOWEVER, THIS SYSTEM IS NOT EXPECTED
TO BE STRONG ENOUGH TO REMOVE THE INVERSION. AS A RESULT, MIXING
HEIGHTS WILL REMAIN LESS THAN 1,500 FEET AGL ON MONDAY, AND
WINDS WILL GENERALLY REMAIN LESS THAN 10 MPH RESULTING IN POOR
VENTILATION. AN ACTIVE PATTERN WILL BRING INCREASED MIXING AND
WINDS, AS WELL AS WIDESPREAD PRECIPITATION, TUESDAY AND
WEDNESDAY WHICH WILL END THE STAGNANT CONDITIONS.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT...A TREND TOWARD
MORE ACTIVE WEATHER WILL DEVELOP OVER THE NEXT COUPLE OF DAYS.
AN UPPER LEVEL RIDGE WILL REMAIN IN PLACE TONIGHT, WITH PATCHY
FOG REDEVELOPING IN THE LOWER TREASURE VALLEY. ON MONDAY
MORNING, A SYSTEM WILL BEGIN TO MOVE INLAND AND BRING LIGHT
PRECIPITATION TO EASTERN OREGON AND WEST-CENTRAL IDAHO. IT WILL
WEAKEN AS IT ENCOUNTERS THE RIDGE, SO AMOUNTS FROM THIS
ACTIVITY WILL BE MINIMAL (TRACE UP TO 0.05"). COLD AIR TRAPPED
IN THE LOWER VALLEYS OF EASTERN OREGON AND FAR WESTERN IDAHO
WILL RESULT IN A SLIGHT CHANCE OF FREEZING RAIN. HOWEVER, ANY
AMOUNTS WILL BE VERY LIGHT, LIMITING ANY IMPACTS. LIGHT SNOW
WILL BE POSSIBLE DOWN TO AROUND 4000 FEET BEFORE SNOW LEVELS
RISE TO 6500-8000 FEET NORTH AND 7500-9500 FEET SOUTH BY MONDAY
EVENING. THE SYSTEM WILL CONTINUE TO BRING A CHANCE OF RAIN AND
HIGH ELEVATION SNOW INTO TUESDAY WITH LIGHT AMOUNTS EXPECTED.
TEMPERATURES ON MONDAY WILL COOL SEVERAL DEGREES FROM TODAY, BUT
REMAIN 5-15 DEGREES ABOVE NORMAL. HOWEVER, ON TUESDAY, HIGH
TEMPERATURES ESPECIALLY AT LOWER ELEVATIONS WILL RISE BY 5-10
DEGREES AS THE INVERSION IS FINALLY ERODED.
A DEEP TROUGH WILL MOVE ONSHORE INTO BRITISH COLUMBIA TUESDAY
NIGHT, SENDING A MORE SIGNIFICANT PLUME OF MOISTURE INTO OUR
REGION. PRECIPITATION CHANCES WILL RISE TO 40-60% IN THE LOWER
ELEVATIONS, AND 60-90% IN THE MOUNTAINS. SNOW LEVELS WILL REMAIN
HIGH THROUGH TUESDAY NIGHT AT AROUND 6500-8000 FEET, BUT 2-4
INCHES OF SNOW ARE EXPECTED BY LATE TUESDAY NIGHT ON HIGHER
PEAKS. MEANWHILE, A TIGHT SURFACE PRESSURE GRADIENT WILL DEVELOP
OVER OUR AREA AS A DEEP SURFACE LOW TRACKS INLAND NEAR THE
U.S./CANADA BORDER. THIS WILL COMBINE WITH STRONG WINDS ALOFT
(50-70KT AT 700 MB) TO PRODUCE WINDY CONDITIONS TUESDAY NIGHT,
STRONGEST ON RIDGELINES AND ACROSS SOUTHEAST OREGON AND FAR
SOUTHWEST IDAHO SOUTH OF THE SNAKE RIVER WHERE GUSTS 40-60 MPH
WILL DEVELOP. WIND HEADLINES WILL LIKELY BE NEEDED IN SOME AREAS
AS THIS SYSTEM APPROACHES.
LONG TERM...WEDNESDAY THROUGH SUNDAY...A POTENT, UPPER-LEVEL
DISTURBANCE WILL MOVE OVER THE AREA ON WEDNESDAY. SIGNIFICANT
PACIFIC MOISTURE WILL ACCOMPANY THIS TROUGH, BUT SO WILL A VERY
STRONG MID-LEVEL JET. PRECIPITATION WILL BE UNDER THE EFFECTS OF
SHADOWING IN VALLEY AREAS CAUSING LOWER AMOUNTS, HOWEVER, A
COLD FRONT MOVING THROUGH THE AREA WEDNESDAY MORNING AND
AFTERNOON SHOULD HELP POP CHANCES AREAWIDE. SNOW LEVELS WILL
BEGIN AROUND 6000-8000 FT MSL WEDNESDAY MORNING AND RAPIDLY DROP
FROM NORTH TO SOUTH TO 3000-5000 FT MSL BY AFTERNOON. SURFACE
WINDS WILL RESPOND ACCORDINGLY TO THIS STRONG MID-LEVEL JET AND
COLD FRONT WEDNESDAY MORNING AND AFTERNOON, WITH WIDESPREAD WIND
GUSTS OF 30+ MPH (WITH HIGHER RIDGETOPS GETTING 50+ MPH) ACROSS
EASTERN OREGON AND THE MOUNTAINS OF SOUTHWEST IDAHO. THIS WOULD
RESULT IN BLOWING/DRIFTING SNOW AND VISIBILITY ISSUES FOR THE
HIGHER TERRAIN. ADDITIONALLY, TEMPERATURES WILL BECOME SEVERAL
DEGREES COOLER ON WEDNESDAY/WEDNESDAY NIGHT COMPARED TO TUESDAY,
PARTICULARLY FOR THE NORTHERN AREAS AND ALSO THE MOUNTAINS
WHERE PRECIPITATION IS HEAVIEST. COMPARED TO THE NORMAL,
HOWEVER, IT WILL STILL BE ABOVE AVERAGE TEMPERATURES.
DRIER NORTHWESTERLY FLOW WILL ESTABLISH BEHIND THE TROUGH
WEDNESDAY NIGHT INTO EARLY THURSDAY, WITH A CHANCE (10-25%) OF
LINGERING SHOWERS. THIS BRIEF RESPITE FROM PRECIPITATION WILL BE
SHORT LIVED, AS A SIGNIFICANT PLUME OF SUBTROPICAL MOISTURE
(ATMOSPHERIC RIVER) IMPACTS THE PACIFIC NW ON THURSDAY. THIS
EVENT WILL BE LONGER DURATION THAN THE PREVIOUS, LASTING FROM
THURSDAY THROUGH AT LEAST EARLY SATURDAY. SNOW LEVELS WILL
OSCILLATE QUITE A BIT DURING THIS PERIOD: STARTING 3000-5000 FT
MSL THURSDAY MORNING, APPROXIMATELY 4500-6500 FEET ON THURSDAY
INTO FRIDAY, THEN LOWERING TO 2500-5000 FEET (LOWEST ALONG
NORTHERN CWA BORDER) BY LATE FRIDAY/EARLY SATURDAY WITH ANOTHER
COLD FRONT AS PRECIP BEGINS TO DECREASE. OVERALL, MOUNTAINS
COULD SEE 1 TO 2 INCHES OF LIQUID EQUIVALENT THROUGHOUT THIS
PERIOD, ALONG WITH HEFTY SNOWFALL TOTALS DEPENDING ON THE SNOW
LEVEL. NOTABLE RAINFALL OVER SATURATED, STEEP TERRAIN WILL ALSO
INTRODUCE ROCKSLIDE CONCERNS. WHILE FLOODING IS CURRENTLY NOT
EXPECTED, RIVERS AND STREAMS AT LOW/MID ELEVATIONS WILL SWELL
RESULTING FROM MULTIPLE DAYS OF ABOVE AVERAGE RAINFALL.
MEANWHILE, TEMPERATURES WILL STAY ABOVE NORMAL FOR MOST AREAS
THURSDAY AND FRIDAY, WITH THE COLDEST AIR EXPECTED ACROSS WEST-
CENTRAL/CENTRAL IDAHO.
BOI WATCHES/WARNINGS/ADVISORIES
ID...AIR STAGNATION ADVISORY UNTIL 5 AM MST TUESDAY
IDZ011>014-016-028-033.
OR...AIR STAGNATION ADVISORY UNTIL 5 AM MST /4 AM PST/ TUESDAY
ORZ061>064.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
DISCUSSION...JDS
AVIATION.....JM
AIR STAGNATION...ST
SHORT TERM...ST
LONG TERM....CH
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page