630
FXUS66 KOTX 212227
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
227 PM PST SAT DEC 21 2024
SYNOPSIS
UNSETTLED WEATHER WILL RETURN THIS WEEKEND AND CONTINUE INTO NEXT
WEEK. MILD TEMPERATURES WILL RESULT IN PRECIPITATION FALLING
PRIMARILY AS VALLEY RAIN AND MOUNTAIN SNOW. CHECK MOUNTAIN PASS
FORECASTS AND CONDITIONS OFTEN BEFORE TRAVELING. PERIODS OF HEAVY
MOUNTAIN SNOW WILL BE POSSIBLE LATE NEXT WEEK.
DISCUSSION
TONIGHT THROUGH MONDAY: A LARGE LOW NEAR THE ALEUTIAN ISLANDS WILL
SEND ADDITIONAL WEATHER SYSTEMS IN FROM THE SOUTHWEST RESULTING IN
A MILD AND WET PATTERN. THE FIRST WAVE MOVING IN TODAY WILL BRING
CONTINUED WIDESPREAD PRECIPITATION WITH THE MAIN FOCUS THIS
EVENING SHIFTING FROM EASTERN WASHINGTON INTO THE ID PANHANDLE
WHILE CENTRAL WA BEGINS TO DRY OUT. PRECIPITATION WILL FALL MAINLY
AS VALLEY RAIN AND MOUNTAIN SNOW AS SNOW LEVELS FALL TO 3500-4000
FEET. THIS WILL RESULT IN LIGHT ACCUMULATIONS FOR MANY OF THE
PASSES IN THE CASCADES, SHERMAN PASS, AND LOOKOUT PASS. MODELS
SHOW THE BRUNT OF THE PRECIPITATION OVER LOOKOUT PASS FALLING
PRIOR TO SNOW LEVELS FALLING WITH ACCUMULATIONS LESS THAN 1 INCH.
FOR THE NORTHERN VALLEYS, A FEW POCKETS OF NEAR FREEZING
TEMPERATURES REMAIN WHERE LOCALIZED FREEZING RAIN IS POSSIBLE. A
WINTER WEATHER ADVISORY REMAINS IN PLACE FOR THE OKANOGAN VALLEY
THROUGH 6 PM FOR A WINTRY MIX. A SHORT WAVE RIDGE MOVES IN
OVERNIGHT INTO SUNDAY MORNING WHICH WILL PROMOTE AN ABUNDANCE OF
STRATUS AND AREAS OF FOG AND FREEZING FOG. THE NEXT SYSTEM SPREADS
MORE VALLEY RAIN AND MOUNTAIN SNOW ACROSS THE REGION STARTING IN
THE CASCADES SUNDAY AFTERNOON BEFORE SPREADING INTO EASTERN WA/N
IDAHO SUNDAY NIGHT. SNOW AMOUNTS IN THE MOUNTAINS WILL GENERALLY
BE 1 TO 3 INCHES, EXCEPT CLOSER TO 4-5 INCHES FOR STEVENS PASS.
ONE EXCEPTION TO THE VALLEY RAIN IS THE METHOW VALLEY, AND EAST
SLOPE VALLEYS. NAM SOUNDINGS AS WELL AS HREF SUGGEST A MAINLY SNOW
EVENT FOR THE METHOW VALLEY WITH 1-3 INCHES, WITH PRECIPITATION
POSSIBLY STARTING AS SNOW AROUND LAKE WENATCHEE WITH 1-2", AND A
RAIN/SNOW MIX FOR LEAVENWORTH AREA. JW
MONDAY NIGHT THROUGH SATURDAY: MUCH OF NEXT WEEK LOOKS TO BE QUITE
UNSETTLED WITH THE GREATEST POTENTIAL FOR SNOW BEING WEDNESDAY
NIGHT THROUGH THURSDAY. CHRISTMAS EVE (MONDAY) WILL FEATURE SOME
CHANCES FOR SNOW AS A COMPACT LOW PRESSURE SYSTEM APPROACHES THE
SW BC COAST. SNOW LEVELS WILL BE AROUND 2000 FEET IN THE EAST
SLOPES OF THE CASCADES AND NORTHERN MOUNTAINS OVERNIGHT.
PRECIPITATION TYPE WILL BE RAIN MOSTLY EVERYWHERE ELSE. LOW LEVEL
UPSLOPE FLOW AND WEAK ISENTROPIC ASCENT IN THE 290-295K LAYER
SUPPORT A LIGHT BURST OF SNOW OVERNIGHT MONDAY IN THE EAST SLOPES
OF THE CASCADES. THE GREATEST CHANCES FOR 1+” OF SNOW IS FROM
LEAVENWORTH TO STEVENS PASS ON US-2 (40-90% CHANCE), TWISP TO
MAZAMA ON HIGHWAY 20 (90% CHANCE), AND WAUCONDA PASS TO SHERMAN
PASS ON HIGHWAY 20 (70% CHANCE).
CHRISTMAS DAY APPEARS TO FEATURE A SHORT BREAK FOR SOME IN BETWEEN
SYSTEMS WITH A SHORTWAVE RIDGE QUICKLY TRAVERSING THROUGH THE
REGION. THE EAST SLOPES OF THE CASCADES HAS THE BEST CHANCE OF
SEEING SNOWFALL ON CHRISTMAS NIGHT AS THE NEXT SYSTEM MOVES IN.
THIS NEXT SYSTEM LOOKS MORE ROBUST FOR SNOWFALL PER ENSEMBLE
GUIDANCE. ISENTROPIC ASCENT LOOKS STRONGER THAN THE TUESDAY
SYSTEM. FROM 4PM WED - 4 PM THURSDAY, STEVENS PASS HAS A 50%
CHANCE OF 12+” OF SNOW. THE SNOWFALL HAS BEEN TRENDING UP ON THE
CMC/EC ENSEMBLES BUT THE GEFS IS HOLDING STEADY BELOW 12” AS THE
MOISTURE PLUME GOES SOUTH OF US. DETAILS WILL BE IRONED OUT AS THE
EVENT COMES CLOSER. LOWLAND LOCATIONS ALSO CARRY LARGE ENSEMBLE
SPREAD, BUT THE 10TH PERCENTILE ACCUMULATIONS ARE 2+” FOR
LEAVENWORTH, WINTHROP, AND REPUBLIC.
THE PARENT TROUGH STILL LINGERS OVER THE NORTHERN PACIFIC INTO THE
LATE WEEK AND NEXT WEEKEND, KEEPING THE ACTIVE WINTRY-ISH PATTERN
ALIVE AND WELL. DB
AVIATION
18Z TAFS: FOG AND LOW STRATUS IS EXPECTED TO LINGER OVER PORTIONS
OF NE WA/N IDAHO PANHANDLE INTO THE AFTERNOON, WITH A TENDENCY TO
BREAKUP AT KGEG/KSFF/KCOE AHEAD OF AN INCOMING WEATHER SYSTEM.
LIGHT RAIN HAS ALREADY STARTED AT WENATCHEE AND WINTHROP AND WILL
SPREAD EAST TROUGH THE AFTERNOON. WIDESPREAD MVFR CONDITIONS AND
LOCALIZED IFR CONDITIONS ARE EXPECTED WITH PRECIPITATION THIS
AFTERNOON AND EVENING WITH AN ABUNDANCE OF IFR STRATUS TONIGHT
INTO SUNDAY MORNING DUE TO A SATURATED BOUNDARY LAYER. THE ONE
EXCEPTION IS PULLMAN AND LEWISTON WHERE THE HREF GUIDANCE IS
FAVORING A BETTER CHANCE FOR VFR CONDITIONS.
FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
POCKETS OF FREEZING TEMPERATURES AROUND OMAK THIS MORNING HAS
RESULTED IN -FZRA REPORTED AT 18Z. THIS ACTIVITY MAY CONTINUE
THROUGH 20Z AND THEN A WINTRY MIX RAIN AND SNOW 20Z-24Z.
CONFIDENCE IS HIGH THAT PRECIPITATION WILL FALL AS RAIN FOR ALL
TAF SITES. JW
-----------------------
CONFIDENCE DESCRIPTORS:
LOW - LESS THAN A 30 PERCENT CHANCE
MODERATE - 30 TO 70 PERCENT CHANCE
HIGH - GREATER THAN A 70 PERCENT CHANCE
FOR ADDITIONAL PROBABILISTIC INFORMATION FOR NWS SPOKANE AIRPORTS,
PLEASE REFER TO THE AVIATION DASHBOARD ON OUR WEBPAGE:
HTTPS:/WWW.WEATHER.GOV/OTX/AVNDASHBOARD
PRELIMINARY POINT TEMPS/POPS
SPOKANE 33 40 36 40 35 41 / 90 10 100 10 40 70
COEUR D'ALENE 32 40 34 41 34 40 / 100 10 100 30 30 70
PULLMAN 33 44 38 45 37 41 / 90 10 100 20 40 70
LEWISTON 36 48 40 50 39 46 / 70 10 90 20 30 60
COLVILLE 29 36 33 38 32 36 / 100 30 100 10 40 80
SANDPOINT 31 37 33 39 33 36 / 100 10 100 70 30 80
KELLOGG 34 40 34 39 33 39 / 100 10 100 80 30 80
MOSES LAKE 32 40 35 42 36 45 / 20 40 80 0 70 60
WENATCHEE 31 36 32 39 34 40 / 10 70 80 0 80 50
OMAK 29 35 32 38 34 37 / 50 40 90 0 70 60
OTX WATCHES/WARNINGS/ADVISORIES
ID...NONE.
WA...WINTER WEATHER ADVISORY UNTIL 6 PM PST THIS EVENING FOR OKANOGAN
VALLEY.
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