838
FXUS65 KBOI 192111
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
211 PM MST MON JAN 19 2026
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
UNDERPERFORMS 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
EASTERN 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.
AVIATION
MVFR-LIFR BELOW 5KFT MSL IN THE SNAKE PLAIN AND
SURROUNDING BASINS DUE TO PERSISTENT LOW STRATUS AND FOG. CLOUDS
WILL LOWER AGAIN TONIGHT, PUSHING CONDITIONS BACK DOWN TO IFR-LIFR.
STRATUS/FOG MAY REACH KBNO TONIGHT. SURFACE WINDS: VARIABLE LESS
THAN 6 KT. WINDS ALOFT AT 10KFT MSL: N 5-15 KT.
KBOI...MVFR CEILINGS EXPECTED THROUGH THE DAY WITH LOW STRATUS, BACK
DOWN TO IFR-LIFR TONIGHT. SURFACE WINDS: VARIABLE UP TO 6 KT.
AIR STAGNATION
THE STRONG TEMPERATURE INVERSION WILL REMAIN
IN PLACE THROUGH AT LEAST THURSDAY MORNING. ATMOSPHERIC MIXING
HEIGHTS ARE FORECAST TO REMAIN VERY LOW, GENERALLY BELOW 1500
FEET, WITH WEAK TRANSPORT WINDS. THIS SETUP WILL CONTINUE TO
TRAP POLLUTANTS NEAR THE SURFACE IN VALLEY LOCATIONS, LEADING TO
DETERIORATING AIR QUALITY OVER TIME. AN AIR STAGNATION ADVISORY
REMAINS IN EFFECT FOR ALL VALLEY ZONES IN SOUTHEAST OREGON AND
SOUTHWEST IDAHO THROUGH THURSDAY MORNING. RELIEF IS NOT EXPECTED
UNTIL A PATTERN CHANGE ARRIVES LATE IN THE WEEK.
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
SHORT TERM...JDS
LONG TERM....JM
AVIATION.....JM
AIR STAGNATION...JDS
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