092
FXUS65 KBOI 200352
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
852 PM MST MON JAN 19 2026
DISCUSSION
DESPITE SLIGHT COOLING ALOFT FROM A WEAK CANADIAN
DISTURBANCE, MOUNTAIN TEMPERATURES STILL ROSE ABOVE FREEZING
FOR MANY SITES THIS AFTERNOON. THIS EVENING, MOUNTAINS ARE NOW
RUNNING A FEW DEGREES COOLER THAN THIS TIME YESTERDAY WITH THE
ENHANCED NORTHERLY FLOW. THE VALLEY COLD POOLS AND ASSOCIATED
STRATUS/FOG PREVAIL, WHICH HAS EVEN EXPANDED IN SOME AREAS SUCH
AS HARNEY COUNTY, BOISE MOUNTAINS, CAMAS PRAIRIE, ETC. PATCHY,
DENSE, FREEZING FOG CAN BE SEEN ON WEBCAMS IN THE BOISE
FOOTHILLS, EAST-CENTRAL OREGON, AND PORTIONS OF THE MAGIC
VALLEY, AS WELL...AND IS UNDOUBTEDLY DEPOSITING ICE ON ROADWAYS
AND SIDEWALKS. THERE IS LOW FORECAST CONFIDENCE THAT TUESDAY'S
WEAK TROUGH WILL ERODE MUCH OF THE STRATUS DECK.
AVIATION
MVFR-LIFR BELOW 5K-6K FEET MSL IN THE SNAKE PLAIN
AND SURROUNDING BASINS DUE TO PERSISTENT LOW STRATUS AND FOG.
STRATUS/FOG MAY REACH KBNO OVERNIGHT AS IT CREEPS WESTWARD.
LOWER MOUNTAINS/FOOTHILLS OBSCURED. SURFACE WINDS: VARIABLE LESS
THAN 8 KT. WINDS ALOFT AT 10KFT MSL: NW 10-20 KT, INCREASING TO
NW-N 15-30 KT AROUND TUE/15Z.
KBOI...IFR-LIFR CEILINGS EXPECTED OVERNIGHT, RISING TO MVFR-IFR
BY LATE TUE MORNING. EXPECT OCCASIONAL SNOW GRAINS OUT OF THE
STRATUS. SURFACE WINDS: LIGHT AND VARIABLE OVERNIGHT, THEN NW
AROUND 5 KT TUE AFTERNOON.
AIR STAGNATION
A STRONG TEMPERATURE INVERSION WITH LIGHT
BOUNDARY LAYER WINDS WILL CONTINUE TO SUPPORT STAGNANT VALLEY
CONDITIONS ACROSS SOUTHEAST OREGON AND SOUTHWEST IDAHO. MIXING
HEIGHTS ARE EXPECTED TO REMAIN AT OR BELOW 2000 FT AGL THROUGH
THURSDAY MORNING, AND THEREFORE AN AIR STAGNATION ADVISORY
REMAINS IN EFFECT UNTIL THEN. COOLING ALOFT SHOULD WEAKEN THE
INVERSION LATE IN THE WEEK AS UPPER LEVEL DISTURBANCES ARRIVE
FROM CANADA.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT...A STRONG UPPER
LEVEL RIDGE REMAINS THE DOMINANT FEATURE OVER THE REGION,
MAINTAINING A STEEP TEMPERATURE INVERSION AND STAGNANT
CONDITIONS. VISIBLE SATELLITE IMAGERY SHOWS NO SIGNIFICANT
CHANGES TO THE PERSISTENT STRATUS DECK ENTRENCHED ACROSS THE
SNAKE PLAIN AND THE LOWER VALLEYS OF SOUTHEAST OREGON. NO
EROSION HAS BEEN OBSERVED, AND THE STRATUS IS ACTUALLY SHOWING
SIGNS OF EXPANSION ACROSS SOUTHEAST OREGON. THIS EXPANSION IS
EXPECTED TO REACH THE LOWER VALLEYS OF HARNEY COUNTY, INCLUDING
BURNS, TONIGHT AND PERSIST THROUGH THE SHORT TERM.
A WEAK SHORTWAVE TROUGH PASSING WELL EAST OF THE FORECAST AREA
EARLY TUESDAY IS UNLIKELY TO BE STRONG ENOUGH TO ERODE THE
STRATUS DECK. THUS, WIDESPREAD LOW CLOUDS WILL REMAIN TRAPPED
WITHIN THE COLD POOLS OF THE TREASURE VALLEY, SNAKE PLAIN, AND
BAKER VALLEY. PATCHY DENSE FOG IS LIKELY AGAIN DURING THE LATE
NIGHT AND MORNING HOURS WHERE THE STRATUS INTERSECTS THE
TERRAIN. AN INCREASE IN MID-LEVEL CLOUDS TUESDAY MORNING COULD
HELP PRODUCE FLURRIES IN THE LOWER STRATUS-FILLED VALLEYS AS THE
HIGHER CLOUDS SEED THE LOWER DECK.
MODELS HAVE POORLY HANDLED THE STRATUS AND RESULTING
TEMPERATURES THUS FAR, PARTICULARLY THE NBM WHICH HISTORICALLY
UNDER-PERFORMS WITH VALLEY INVERSION EVENTS. CONSEQUENTLY, THE
FORECAST WEIGHS PERSISTENCE HEAVILY AGAINST STATISTICAL
GUIDANCE. TEMPERATURES WILL REMAIN INVERTED, WITH VALLEY
LOCATIONS STRUGGLING TO WARM OUT OF THE FREEZING RANGE, WHILE
MOUNTAIN LOCATIONS ABOVE THE INVERSION LAYER (ROUGHLY 5000 TO
6000 FEET MSL) EXPERIENCE MOSTLY SUNNY SKIES AND MILD
TEMPERATURES IN THE 40S AND LOW 50S. LITTLE CHANGE IS EXPECTED
THROUGH WEDNESDAY AS THE RIDGE AXIS SHIFTS SLOWLY OVERHEAD, WITH
VALLEY STRATUS AND FOG HEAVILY INFLUENCING DAILY HIGH AND LOW
TEMPERATURES IN THE LOWER ELEVATIONS.
LONG TERM...THURSDAY THROUGH MONDAY...THE LATEST MODEL TRENDS SEEM
TO BE HOLDING FIRM, AS A CUTOFF LOW SETS UP OFF THE CALIFORNIA COAST
AND A GREAT LAKES LOW BECOMES THE PRIMARY DRIVER OF WEATHER OVER THE
CONUS. FOR US, HOWEVER, THIS MEANS INSIGNIFICANT WEATHER IN THE
DEFORMATION ZONE WITH SOME INCREASED CLOUDS AND A REDEVELOPED RIDGE
OFF THE PACNW COAST. THE LAKES LOW'S LARGE PRESSURE GRADIENT MOVES
INTO THE MID-LEVELS, AND WITH SOME CLOUD COVER AND COLDER AIR
ALOFT, THIS MAY BE ENOUGH TO BRIEFLY WEAKEN OR BREAK THE
INVERSION ON FRIDAY AND SATURDAY BEFORE THAT RIDGE RETURNS ON
SUNDAY. THE POTENTIAL PRECIP HAS BEEN PUSHED BACK TO
SUNDAY/MONDAY, WITH THE MAIN COMPONENT BEING WARM AND MOIST
ZONAL FLOW SETTING UP ON MONDAY. THIS IS AT LEAST A MORE
RELIABLE SOURCE OF PRECIPITATION THAN THE WESTERN EDGE OF A
LAKES LOW WOULD BE, BUT IN THE CURRENT FORECAST WE ARE JUST ON
THE SOUTHERN EDGE OF THE MOISTURE WITH SOME HINTS OF RIDGING
STILL OFF THE COAST.
BOI WATCHES/WARNINGS/ADVISORIES
ID...AIR STAGNATION ADVISORY UNTIL 11 AM MST THURSDAY
IDZ011>014-016-028-033.
OR...AIR STAGNATION ADVISORY UNTIL 11 AM MST /10 AM PST/ THURSDAY
ORZ061>064.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
DISCUSSION...SH
AVIATION.....SH
AIR STAGNATION...SH
SHORT TERM...JDS
LONG TERM....JM
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