310
FXUS65 KBOI 190347
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
847 PM MST SUN JAN 18 2026
DISCUSSION
THE BROAD AREA OF LOW STRATUS AND FOG REMAINS
WELL-ESTABLISHED ACROSS THE LOWER VALLEYS TONIGHT, WHILE ALSO
EXPANDING ACROSS SOUTH-CENTRAL ID AND UP THE VALLEYS IN THE
BOISE MOUNTAINS. WEBCAMS AND OBSERVATIONS DEPICT AREAS OF DENSE
FOG ACROSS THE MAGIC VALLEY AND IMPACTING I-84 AND US-93, WHICH
HAS WARRANTED A DENSE FOG ADVISORY TO REMAIN IN EFFECT THROUGH
AT LEAST MONDAY MORNING. FOG IS EXPECTED TO LIFT ABOVE THE
SURFACE THROUGH MONDAY AFTERNOON FOR MOST AREAS AS GENTLE
VERTICAL MIXING OCCURS. HI-RES MODELS SUGGEST THE STRATUS WILL
TEMPORARILY RETREAT FROM E TO W FOR THE MAGIC VALLEY AND
PORTIONS OF THE UPPER TREASURE VALLEY THROUGHOUT THE AFTERNOON
AND EVENING, AS A WEAK UPPER DISTURBANCE PASSES THROUGH EASTERN
IDAHO.
AVIATION
WIDESPREAD IFR/LIFR BELOW 5000FT MSL FROM THE MAGIC
VALLEY OF IDAHO TO THE LOWER TREASURE VALLEY OF OREGON.
MOUNTAIN OBSCURATION BELOW APPROX 5000FT MSL, WHILE HIGHER
ELEVATIONS REMAIN CLEAR. SURFACE WINDS: VARIABLE LESS THAN 6 KT.
WINDS ALOFT AT 10KFT MSL: N-NW 10-25 KT.
KBOI...GENERALLY IFR/LIFR IN PERSISTENT LOW STRATUS ALONG WITH
VISIBILITY RESTRICTIONS AT TIMES DUE TO MIST. BEST CHANCE FOR
LIFR CEILINGS WITH REDUCED VISIBILITY 08Z-17Z MONDAY. SURFACE
WINDS: VARIABLE UP TO 5 KT.
AIR STAGNATION
DOMINATING HIGH PRESSURE WILL CONTINUE TO
PROMOTE STAGNANT CONDITIONS ACROSS THE REGION THROUGH THURSDAY.
EXPECT LIGHT WINDS AND LITTLE VERTICAL MIXING AS MIXING HEIGHTS
REMAIN AT/BELOW 2000 FEET AGL. THE TEMPERATURE INVERSION WILL
CONTINUE TO TRAP POLLUTANTS NEAR THE SURFACE WHILE LOW CLOUDS
AND FREEZING FOG REMAIN ENTRENCHED ACROSS LOWER VALLEYS AND
BASINS.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT...STRATUS HELD ON
REALLY STRONG TODAY, IN LINE WITH THINKING FROM YESTERDAY, BUT
SHOWING ALMOST NO SIGNS OF DISSIPATION. IT'LL LIKELY STICK
AROUND THROUGH TONIGHT, WITH SLIGHT LOWERING TO BRING FOG BACK
TO SOME RELATIVE HIGH POINTS AROUND THE SNAKE PLAIN AND
SURROUNDING BASINS, ESPECIALLY NEAR THE EDGE OF THE STRATUS SUCH
AS IN THE MAGIC VALLEY. THIS MORNING'S DENSE FOG ADVISORY WAS
EXPIRED AFTER AN EXTENSION, AND WE ANTICIPATE MORE DENSE FOG TO
FORM TONIGHT. THE OVERALL PATTERN REMAINS THE SAME, A RIDGE SITS
OVER US, KEEPING CONDITIONS DRY AND INVERTED. STAGNANT AIR IS
PRESENT IN MANY OF OUR VALLEYS. WE EXPECT THE VALLEY FOG/STRATUS
TO CONTINUE THROUGH THE SHORT TERM WITH DAILY HIGH TEMPERATURES
5-10 DEGREES COLDER THAN NORMAL UNDER THE STRATUS.
LONG TERM...WEDNESDAY THROUGH SUNDAY...THE UPPER LEVEL RIDGE
WILL REMAIN OVERHEAD THROUGH THURSDAY MORNING. THE PATTERN GETS
A LITTLE TRICKY AS THE UPSTREAM WAVE BREAKS INTO A CUT OFF LOW
OFF THE CALIFORNIAN COAST. AMONGST MOST GUIDANCE THIS INCREASES
CLOUD COVER FOR OUR AREA BRINGING A WEAK TROUGH AXIS THROUGH
FROM A DEEP HUDSON BAY LOW. HOWEVER, COMPARED TO PREVIOUS RUNS
THIS IS A LESS SIGNIFICANT SET UP FOR OUR AREA. THE CUT OFF LOW
WOULD CARRY MOST OF ITS ENERGY AWAY FROM OUR AREA, PREVENTING
PRECIPITATION THURSDAY-FRIDAY MORNING. BY FRIDAY EVENING THE CUT
OFF LOW BEGINS MAKING LANDFALL IN SOCAL AS IT REJOINS THE
PRIMARY LOW, TOO FAR EAST TO CARRY PRECIP THROUGH THE AREA
AGAIN. DETERMINISTIC GUIDANCE FOR SATURDAY-SUNDAY HAS TRENDED
TOWARDS A SLIGHT RIDGE. WHILE THIS SEEMS TO BE THE MEAN OUTCOME,
THERE IS STILL A STRONG CONTINGENT OF GUIDANCE SHOWING A MORE
UNSETTLED PATTERN WITH ZONAL FLOW ALOFT. IF WE DON'T GET A
PRECIPITATION EVENT OR A DECENT WAVE THROUGH THE AREA, WE COULD
SEE THE INVERSION HANG ON FOR A FEW MORE DAYS.
BOI WATCHES/WARNINGS/ADVISORIES
ID...AIR STAGNATION ADVISORY UNTIL 11 AM MST THURSDAY
IDZ011>014-016-028-033.
DENSE FOG ADVISORY UNTIL 11 AM MST MONDAY IDZ016.
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.....MC
AIR STAGNATION...SH
SHORT TERM...JM
LONG TERM....JM
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page