098
FXUS66 KOTX 210547
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
947 PM PST FRI DEC 20 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
SUNDAY THROUGH TUESDAY: SEVERAL WEAK STORM SYSTEMS WILL PASS THROUGH
THE PACNW DELIVERING LOWLAND RAIN AND MOUNTAIN SNOW. THIS IS WELL
AGREED UPON AMONGST THE ENSEMBLE FORECAST SUITES AND CONFIDENCE
IS ABOVE NORMAL. THE MAIN CHALLENGE WITH THESE SYSTEMS WILL BE
FLUCTUATING SNOW LEVELS, PARTICULARLY IN THE VALLEYS OF THE
CASCADE EAST SLOPES AND AROUND THE COMMUNITIES NEAR THE CANADIAN
BORDER INCLUDING REPUBLIC, LAURIER, METALINE FALLS, AND BONNERS
FERRY. PRECIPITATION TYPE IN THESE AREAS CARRIES THE MOST
UNCERTAINTY WITH THE POTENTIAL TO FALL AS SNOW, WET SNOW, OR
POTENTIALLY SWITCH TO ALL RAIN. NATIONAL BLEND OF MODELS IS
INDICATING ALL RAIN BUT TENDS TO STRUGGLE WITH THE THERMAL
PROFILES IN THESE VALLEYS AND FORECAST SNOW LEVELS WERE TRENDED
DOWN CLOSER TO THE MAXIMUM WET BULB TEMPERATURES IN THE LAYER.
THINKING THERE WILL BE SEVERAL PERIODS WHEN THE TEMPERATURES RISE
ABOVE FREEZING AND WET, NON-ACCUMULATING SNOW FALLS. ON THE
CONTRARY, PERIODS WHEN LIFT IS MAXIMIZED IN THE ATMOSPHERE (AKA
OMEGA IN THE DENDRITIC LAYER IS HIGH), WET SNOW ACCUMULATIONS WILL
BE A STRONG POSSIBILITY EVEN WITH TEMPERATURES OF 32-34F. MOST
OTHER AREAS WILL BE MAINLY RAIN.
CONFIDENCE IS HIGHER FOR SNOW TO FALL ON THE PASSES BUT GIVEN THE
RISING SNOW LEVELS, SNOW WILL AT TIMES ONLY RESULT IN WET, SLUSHY
ACCUMULATIONS AND OTHER TIMES, WINTER DRIVING CONDITIONS. IF YOU
ARE TRAVELING OVER THE PASSES, BE SURE TO KEEP UP TO DATE ON THE
LATEST FORECAST AND CONDITIONS AND PLAN ACCORDINGLY TO MEET YOUR
NEEDS.
AS FOR TIMING, THE FIRST SYSTEM WILL ARRIVE IN THE CASCADES ON SUNDAY
AND EXPAND ACROSS EASTERN WA AND NORTH IDAHO SUNDAY NIGHT.
PRECIPITATION INTENSITIES IN THE CASCADES WILL BE LIGHT THROUGH
SUNSET AND INCREASE SUNDAY EVENING. A COLD FRONT SWEEPING THROUGH
WILL END PRECIPITATION IN THE LEE OF THE CASCADES BY MONDAY
MORNING WITH SNOW SHOWERS CONTINUING ON THE CREST AND POSSIBLY THE
PASSES. IDAHO AND SOUTHEASTERN WA WILL HAVE THE BEST POTENTIAL
FOR MODERATE PRECIPTIATION RATES WHICH COME EARLY MONDAY MORNING.
MUCH OF THE INW WILL DRY OUT FOR MONDAY AFTERNOON.
THE SECOND SYSTEM ARRIVES MONDAY NIGHT INTO TUESDAY MORNING. THERE
WILL BE A STRONGER EASTERLY WIND GRADIENT WITH THIS WAVE SO ANY
COLD AIR TRAPPED IN THE LEE OF THE CASCADES WILL REMAIN FIRMLY IN
PLACE AND KEEP SNOW LEVELS STATUS QUO THROUGH THE PRECIPITATION
AND BASED HOW SNOW LEVELS ARE TRENDING MONDAY AFTERNOON, MODEST
CHANGES TO THE FORECAST P-TYPE ARE A STRONG POSSIBILITY. THIS WILL
BE A WETTER SYSTEM WITH MORE WIDESPREAD 0.10-0.30" QPF AMOUNTS
AND POCKETS NEAR HALF AN INCH. THERE IS A 60% CHANCE OR GREAT FOR
MOST AREAS OUTSIDE THE L-C VALLEY TO RECEIVE 0.20" OF LIQUID.
WEDNESDAY THROUGH FRIDAY: ROUGHLY 45-50% OF THE ENSEMBLES SUPPORT A
SUBTLE SHIFT IN THE JET STREAM ALLOWING TROUGHS TO COME THROUGH
FROM THE WEST VS SOUTHWEST. GIVEN THIS SCENARIO, COOLER AIR WILL
ACCOMPANY ADDITIONAL STORM SYSTEMS ARRIVING LATE CHRISTMAS THROUGH
FRIDAY. THIS WOULD SUPPORT ALL SNOW IN THE MOUNTAINS AND DOWN TO
SOME VALLEY FLOORS FOR ELEVATIONS ABOVE 2000 FEET MAINLY NORTH OF
HIGHWAY 2. I WOULD NOT BANK ON IT QUITE YET GIVEN THE 50/50
PROBABILITIES MENTIONED BUT ITS A SIGN OF LIFE FOR THOSE HOPING
FOR HEAVIER SNOW IN THE MOUNTAINS AND "SLIM" POTENTIAL FOR LOWLAND
SNOW. DETAILS ARE FAR FROM CERTAIN. THE REMAINING 50% CONTINUE A
SIMILAR PATTERN TO THAT IN THE DISCUSSION FOR SUNDAY-TUESDAY
ABOVE. IF YOU ARE TRAVELING BACK FROM GRANDMA'S HOUSE, BE PREPARED
FOR MORE IMPACTFUL SNOW AND POTENTIAL DELAYS ON THE PASSES.
LOWLAND TRAVEL IS LESS LIKELY TO BE IMPACTED BY SIGNIFICANT WINTER
WEATHER BUT CANNOT BE RULED OUT COMPLETELY AT THIS TIME GIVEN THE
SPREAD IN POTENTIAL OUTCOMES.
THESE SYSTEMS LATE WEEK WILL HAVE MODERATE TO HEAVY QPF. IN THE WAKE
OF SEVERAL WET SYSTEMS EARLY IN THE WEEK, MANY STREAMS AND CREEKS
WILL BEGIN TO SEE ELEVATED FLOWS. AREAS THAT REMAIN ALL RAIN
COULD ALSO BE COPING WITH WATER PONDING IN FIELDS. IT APPEARS MUD
SEASON IS MAKING A RETURN FOR SOME. /SB
AVIATION
06Z TAFS: FOG HAS DEVELOPED ACROSS THE NORTHERN VALLEYS AND IS
EXPECTED TO EXPAND INTO THE SPOKANE/CDA AREAS AND THE COLUMBIA
BASIN OVER THE NEXT COUPLE OF HOURS. CEILINGS ARE EXPECTED TO DROP
TO MVFR OR IFR CONDITIONS FOR MOST SITES, WITH THE EXCEPTION OF
KLWS AND KPUW WHICH WILL REMAIN IN VFR CONDITIONS AHEAD OF THE
PRECIPITATION. PRECIPITATION WILL MOVE INTO THE CENTRAL
WASHINGTON BETWEEN 18-20Z AND INTO THE SPOKANE AREA BETWEEN
20-22Z. WIDESPREAD MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS IS
EXPECTED WITH PRECIPITATION SATURDAY AFTERNOON AND EVENING.
FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
THERE IS MODERATE CONFIDENCE FOR FOG AND LOW CLOUDS TO REDEVELOP
IN THE COLUMBIA BASIN OVERNIGHT WITH LOWER CONFIDENCE FOR THE
SPOKANE AREA. THERE IS MODERATE CONFIDENCE IN THE PRECIPITATION
ARRIVAL TIME WITH MINOR DIFFERENCES AMONG THE HI-RES GUIDANCE.
-----------------------
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 32 42 33 42 36 43 / 10 70 80 0 90 20
COEUR D'ALENE 32 42 33 43 35 43 / 10 60 90 0 90 30
PULLMAN 35 44 32 43 37 46 / 0 70 80 0 90 30
LEWISTON 38 47 36 47 40 50 / 0 40 50 0 80 20
COLVILLE 29 38 29 38 33 39 / 10 80 80 20 90 20
SANDPOINT 31 40 34 39 34 40 / 10 60 100 10 90 60
KELLOGG 35 46 36 41 35 41 / 10 60 100 10 90 60
MOSES LAKE 31 39 31 42 34 43 / 10 90 20 30 80 10
WENATCHEE 33 39 31 38 32 40 / 10 90 20 50 90 10
OMAK 31 39 31 38 33 41 / 10 90 30 30 90 10
OTX WATCHES/WARNINGS/ADVISORIES
ID...NONE.
WA...NONE.
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