038
FXUS65 KBOI 190415
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
915 PM MST WED DEC 18 2024
DISCUSSION
A STRONG SYSTEM TO THE NORTH BROUGHT STRONG WINDS
ALOFT OF W-NW 70-80 MPH AT 10,000FT MSL TO SOUTHWEST IDAHO AND
SOUTHEAST OREGON. HIGH CLOUDS LAST NIGHT KEPT TEMPERATURES
RELATIVELY MILD, THIS ALLOWED FOR GOOD MIXING THIS AFTERNOON
WITH MOSTLY SUNNY SKIES. BOISE REACHED 59F DEGREES, BREAKING THE
OLD RECORD OF 58F SET IN 1917. UPPER LEVEL WINDS WILL SLOWLY
SUBSIDE OVERNIGHT. THIS WILL ALLOW TEMPERATURES FALLING INTO THE
DEWPOINTS TONIGHT, WITH LOW CLOUDS AND FOG DEVELOPING ACROSS
THE VALLEYS, ESPECIALLY IN THE LOWER TREASURE AND EASTERN OR
BASINS, ALONG WITH MOUNTAIN VALLEYS. HRRR MODEL SHOWS
TEMPERATURES REACHING THE LOW TO MID 50S AGAIN AT BOI TOMORROW,
BUT WITH THE WINDS ALOFT SUBSIDING, THINK IT WILL BE HARDER TO
WARM THAN IT WAS TODAY. AS THE RIDGE MOVES OVERHEAD, THIS WILL
ALLOW FOG AND STRATUS TO EXPAND EACH NIGHT IN THE LOWEST
ELEVATIONS, ESPECIALLY BELOW 4000 FEET MSL. FOG AND STRATUS WILL
KEEP TEMPERATURES COOLER, WITH ABOVE NORMAL AND SUNNY CONDITIONS
IN THE MOUNTAINS ABOVE THE TEMPERATURE INVERSION. NO UPDATES TO
THE FORECAST.
AVIATION
GENERALLY VFR. LIFR FOG DEVELOPING IN BASINS AND VALLEYS
NEAR KBNO KONO KEUL KMYL KBKE TONIGHT. SOME IMPROVEMENT TO VFR
POSSIBLE THU AFTERNOON, BUT CONFIDENCE LOW. SURFACE WINDS 10KT
OR LESS. WINDS ALOFT AT 10KFT MSL: NW 25-35KT EASING TO NW
15-25KT BY THU MORNING.
KBOI...VFR. LIFR FOG WEST OF THE AIRPORT, BUT 10% CHANCE THAT
IT WILL REACH TERMINAL. SURFACE WINDS: SE 5-10KT SHOULD KEEP FOG
WEST OF AIRPORT.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...WE HAVE MIXED OUT
TODAY MORE THOROUGHLY THAN EXPECTED, WITH TEMPERATURES RISING
ABOVE FORECAST HIGHS. THIS HAS IMPLICATIONS FOR THE FORECAST
GOING FORWARD, SUCH AS LOWERED EXPECTATIONS FOR FOG TONIGHT, AND
A SLOWER RE-DEVELOPMENT OF AN INVERSION. WE STILL SEE AN
INVERSION FORMING, BUT HAVE REDUCED THE AMOUNT OF COOLING IN THE
LOWER TREASURE VALLEY AND SURROUNDING AREAS FOR THU AND FRI.
OTHERWISE, AN UPPER LEVEL RIDGE WILL MOVE ACROSS THE AREA
THURSDAY, BRINGING MOSTLY CLEAR SKIES TO MOST AREAS. SW FLOW
ALOFT WILL MOVE IN BEHIND THIS, WITH WARMER AIR ADVECTING INTO
THE REGION ALOFT WHILE THE INVERSION FORMS AT THE SURFACE. AFTER
A VERY WEAK AND DRY TROUGH SLIDES ACROSS OUR NORTHERN AREA THU,
A SECOND RIDGE AXIS WILL RACE OVERHEAD EARLY FRIDAY. WINDS WILL
INCREASE FRIDAY AFTERNOON GENERALLY FROM THE WESTERN MAGIC
VALLEY WEST INTO THE UPPER TREASURE VALLEY. FRIDAY NIGHT WILL BE
DRY WITH AN INCREASING CHANCE OF LOW CLOUDS AND FOG IN LOWER
ELEVATIONS.
LONG TERM...SATURDAY THROUGH WEDNESDAY...THE BREAKDOWN OF A
PERSISTENT LOW OVER THE HUDSON BAY HAS FINALLY ALLOWED THE STORM
TRACK TO MOVE OVER OUR AREA, KEEPING THINGS WET AND ACTIVE IN THE
LONG TERM. EACH LOW WILL BE WORKING TO BREAK DOWN A RIDGE IN THE
SHORT TERM, SO THE FIRST FEW SYSTEMS, THIS WEEKEND AND MONDAY, ARE
LIKELY TO BE ON THE WEAKER SIDE. ONLY A FEW HUNDREDTHS EXPECTED TO
FALL WITH A SYSTEM LATE SATURDAY INTO EARLY SUNDAY IN THE VALLEYS AS
RAIN. IN THE MOUNTAINS 0.1-0.3 INCHES OF RAINFALL BECOMING A FEW
INCHES OF SNOW ABOVE 5-6 KFT MSL. LATER SUNDAY INTO MONDAY ANOTHER
TROUGH ANOTHER SYSTEM MOVES IN. THIS ONE APPEARS A BIT WETTER,
LIKELY KEYING INTO SOME WEAKENING OF THE POSITIVE HEIGHT
ANOMALIES AFTER SATURDAY, WITH ABOUT 0.1 INCHES OF RAINFALL FOR
VALLEYS AND AGAIN 0.1-0.3 INCHES OF RAIN IN MOUNTAINS WITH A
FEW INCHES OF SNOW ABOVE 5-7 KFT MSL. A THIRD TROUGH IS SLATED
TO MOVE THROUGH TUESDAY EVENING THROUGH CHRISTMAS MORNING, AGAIN
TRENDING WETTER. IN THE VALLEYS 0.1 TO 0.4 INCHES OF RAINFALL,
AND 0.5 TO 1 INCH OF RAINFALL IN THE MOUNTAINS BECOMING 2-8
INCHES OF SNOW ABOVE 5-6 KFT MSL. TEMPS HOLD FAIRLY STEADY
AROUND 5 DEGREES ABOVE NORMAL, WITH SLIGHT COOLING AFTER EACH
TROUGH. UNLESS THE TUESDAY NIGHT TROUGH BECOMES VERY COLD IN THE
NEXT FEW MODEL RUNS, A WHITE CHRISTMAS FOR SNAKE PLAIN
LOCATIONS IS LOOKING UNLIKELY.
BOI WATCHES/WARNINGS/ADVISORIES
ID...NONE.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.TWITTER.COM/NWSBOISE
DISCUSSION...KA
AVIATION.....KA
SHORT TERM...SP
LONG TERM....JM
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