217
FXUS65 KBOI 152153
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
253 PM MST SUN DEC 15 2024
SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT
THE NEXT STORM TO
IMPACT THE AREA IS PUSHING ONTO THE COAST THIS AFTERNOON. LIGHT
PRECIPITATION WILL OVERSPREAD SOUTHEAST OREGON LATE THIS
EVENING, ADVANCING INTO SOUTHWEST IDAHO OVERNIGHT. THE FORECAST
REMAINS CONSISTENT IN PLACING THE AXIS OF HEAVIER PRECIPITATION
FROM NORTHERN HARNEY/MALHEUR COUNTIES INTO THE WEST-CENTRAL
IDAHO MOUNTAINS. SNOW LEVELS WILL START AT VALLEY FLOORS AND
REMAIN LOW THROUGH EARLY AFTERNOON MONDAY, RISING INTO THE
EVENING AS UPPER TROUGH PASSES. THIS WILL TRANSLATE TO LIGHT-
MODERATE SNOWFALL OVER NORTHERN HARNEY AND MALHEUR COUNTIES FROM
ALONG AND NORTH OF HIGHWAY 20. BAKER COUNTY AND THE UPPER WEISER
BASIN WILL ALSO SEE WIDESPREAD ACCUMULATING SNOW. AMOUNTS IN
THESE AREAS WILL GENERALLY RANGE 1 TO 4 INCHES ON VALLEY FLOORS,
TO INCLUDE INTERSTATE 84 WEST OF ONTARIO TO BAKER CITY, AND
HIGHWAY 20 FROM RILEY TO VALE. PROBABILITIES FOR 2 INCHES OR
MORE IN THIS AREA RUN 60-80%, DROPPING TO 20-40% FOR 4" OR MORE.
GUSTY EASTERLY WILL ACCOMPANY THE SNOWFALL IN BAKER COUNTY WHICH
WILL FURTHER IMPACT TRAVEL.
ON THE IDAHO SIDE OF THE SNAKE PLAIN PRECIPIATION WILL START AS
SNOW OR A RAIN/SNOW MIX, BUT EXPECT TEMPERATURES TO BE AT OR
SLIGHTLY ABOVE FREEZING WHICH WILL LIMIT ACCUMULATION,
ESPECIALLY SITES FROM CALDWELL EASTWARD WHICH HOLD ONTO A
STEADY TO SOUTHEAST WIND OVERNIGHT. THESE DOWNSLOPE WINDS WILL
ALSO ACT TO CUT DOWN ON PRECIPITATION REACHING THE GROUND. THE
NBM SHOWS PROBABILITY OF MEASUREABLE SNOW (0.1") RANGING FROM 40
TO 70% THROUGH THE SNAKE PLAIN FROM TWIN/JEROME TO ONTARIO.
MOVING TO AN INCH OR MORE AND THE PROBABILITES DROP TO LESS THAN
10%. THE HREF PAINTS A SIMILAR PICTURE FROM MOUNTAIN HOME TO
ONTARIO, WITH LOWER PROBABILITES IN THE WESTERN MAGIC VALLEY.
THE MOUNTAINS START AS ALL SNOW, WITH SOME LOWER VALLEYS IN THE
BOISE MOUNTAINS MIXING WITH OR CHANGING TO RAIN ON MONDAY AS
SNOW LEVELS RISE TO AROUND 4500 FEET.
RAIN AND SNOW CONTINUE THROUGH TUESDAY MORNING AS A TRAILING
UPPER WAVE CROSSES THE REGION. WITH LITTLE CHANGE IN THE AIR
MASS, VALLEYS WILL STAY RAIN OR RAIN/SNOW MIX WHERE ANY COLD
AIR REMAINS TRAPPED. NO FURTHER ACCUMULATION IS EXPECTED AFTER
TUESDAY AFTERNOON ACROSS LOWER ELEVATIONS. MOUNTAINS WILL
MAINTAIN SNOW LEVELS OF 3500-4500 FEET. MOUNTAIN VALLEYS WILL
SEE 2 TO 5 INCHES THROUGH MONDAY EVENING WITH LIGHT ADDTIONAL
ACCUMUATIONS INTO TUESDAY. HIGHER ELEVATIONS ARE IN LINE FOR
ANOTHER 5 TO 10 INCHES THROUGH TUESDAY AFTERNOON.
LONG TERM...WEDNESDAY THROUGH SUNDAY
AN UPPER LEVEL RIDGE
WILL BUILD IN ON WEDNESDAY MORNING, BRINGING DRY CONDITIONS TO
THE REGION THROUGH SATURDAY. AN INVERSION WILL LIKELY DEVELOP
OVER THE SNAKE RIVER VALLEY, WITH LOW LEVEL STRATUS AND
POTENTIAL FOG IN ADDITION TO BELOW NORMAL TEMPERATURES LIKELY
ACROSS THOSE LOWER ELEVATIONS. CLUSTER SOLUTIONS FAVOR THIS
OUTCOME HEAVILY, WITH MORE UNCERTAINTY PRESENT IN THE
DETERMINISTIC MODELS, WITH SLIGHT VARIATIONS IN TEMPERATURES AND
RIDGE EXTENT OVER THE REGION ON SATURDAY.
BY LATE SATURDAY, MODELS AGREE ON AN INCOMING SYSTEM WEAKENING
SLIGHTLY AS IT MOVES INTO THE RIDGE, BUT BRINGING INCREASED
WESTERLY WINDS AND MOUNTAIN PRECIPITATION. THESE WINDS LOOK TO
SCOUR OUT THE INVERSION, BUT FORECAST CONFIDENCE IS LOW DUE TO
THE LARGE UNCERTAINTY IN POSITION AND STRENGTH OF THE TROUGH.
AVIATION
VFR FOR MOST LOCATIONS. CONTINUING IFR/LIFR AND
MTN OBSCURATION IN SNOW SHOWERS AND LOW STRATUS OVER MOUNTAIN
VALLEYS NEAR KBKE/KMYL. PRECIPITATION SPREADING FROM W TO E
PROMOTING MVFR TO LIFR CONDITIONS AFTER MON/04Z. SNOW LEVELS AT
VALLEY FLOORS, RISING TO 3000-4000 FEET MSL TOMORROW AFTERNOON.
SURFACE WINDS: SW-NW 5-15 KT SHIFTING TO SE-NE 5-15 KT AFTER
MON/03Z. WINDS ALOFT AT 10KFT MSL: W-SW 20-35 KT.
KBOI...VFR TODAY. RAIN/SNOW MIX ARRIVING EARLY MONDAY, WITH A
LOW CHANCE OF A BRIEF SWITCH TO SNOW EARLY MORNING, THEN ALL
RAIN MONDAY AFTERNOON. LOW VFR/MVFR IN PRECIPITATION. LIGHT SNOW
ACCUMULATIONS POSSIBLE EARLY MON. SURFACE WINDS: NW 5-10 KT,
BECOMING SE 5-10 KT AFTER SUNSET.
BOI WATCHES/WARNINGS/ADVISORIES
ID...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 2 PM MST
MONDAY IDZ033.
OR...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 1 PM PST
MONDAY ORZ062.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.TWITTER.COM/NWSBOISE
SHORT TERM...DG
LONG TERM....SA
AVIATION.....SA
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