254
FXUS66 KOTX 172237
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
237 PM PST TUE DEC 17 2024
SYNOPSIS
AN ATMOSPHERIC RIVER OFF OF THE PACIFIC WILL BRING A WINTRY MIX TO
THE REGION TONIGHT. SNOW WILL MAINLY ACCUMULATE OVER HIGH
MOUNTAINS AND IN NORTH-CENTRAL WASHINGTON INCLUDING THE EASTERN
CASCADE VALLEYS. FREEZING RAIN IS EXPECTED ACROSS PORTIONS OF THE
CASCADES AND WATERVILLE PLATEAU THIS EVENING AND THEN SHIFT INTO
PORTIONS OF NORTHERN WA OVERNIGHT. WINDS WILL BECOME BREEZY TO
LOCALLY WINDY WEDNESDAY AFTERNOON. THE REST OF THE WEEK WILL
FEATURE MILD TEMPERATURES AND A TREND OF MORE WET WEATHER TOWARDS
THE WEEKEND INTO NEXT WEEK.
DISCUSSION
***KEY POINTS***
- MODERATE TO HEAVY BURST OF SNOW TO CONTINUE THROUGH THE REST OF
THE AFTERNOON AND EARLY EVENING (60-90% CHANCE OF 1+"/HR
SNOWFALL RATES IN CENTRAL WASHINGTON).
- SNOW CHANGING TO FREEZING RAIN THIS EVENING AT STEVENS PASS. ICE
ACCUMULATIONS AS HIGH AS 0.5" ON TOP OF SNOW IN WESTERN CHELAN
COUNTY.
- GUSTY WINDS EXPECTED TOMORROW MORNING WITH THE COLD FRONT
PASSAGE (20-50% CHANCE OF GUSTS GREATER THAN 50 MPH ON THE
COLUMBIA BASIN, SPOKANE/CDA METRO, PALOUSE, AND WESTERN L-C
VALLEY.
TODAY THROUGH TOMORROW: OVERALL THE FORECAST REMAINS ON TRACK FOR
A BURST OF MODERATE TO HEAVY SNOW THIS AFTERNOON AND EVENING IN
CENTRAL WASHINGTON. ADJUSTMENTS WERE MADE TO BRING DOWN SNOW LEVELS
FOR GEORGE, QUINCY, AND EPHRATA AS WETBULB COOLING HAS TURNED THOSE
LOCATIONS TO SNOW. WITH SURFACE TEMPERATURES AROUND 34 DEGREES IN
THAT CORRIDOR, ROAD ACCUMULATIONS WILL BE FAIRLY LIMITED. THERE IS
HIGH CONFIDENCE OF A HEAVY BURST OF SNOW LATE THIS AFTERNOON AND
THIS EVENING BRINGING 1"+/HR SNOWFALL RATES TO CENTRAL WASHINGTON AS
SURFACE TEMPERATURES WILL STILL SUPPORT SNOW. THE BEST CHANCES (60-
90% CHANCE OF 2 HOURS OF 1+"/HR SNOWFALL RATES) ARE AREAS FROM
STEVENS PASS TO DOUGLAS ON US-2, PATEROS TO MAZAMA ON SR-20, AND US-
97 FROM WENATCHEE TO OMAK. AS THE PARENT LOW APPROACHES THE SW BC
COAST THIS EVENING, SNOW LEVELS WILL SHARPLY RISE IN THE CASCADE
VALLEYS PROMOTING THE CHANGE OF SNOW TO FREEZING RAIN. THE BEST
CHANCE (70%) 0.25"+ OF ICE IS BETWEEN COLES CORNER AND STEVENS PASS
BETWEEN 4 PM AND 4 AM TONIGHT. THIS IS WHAT PROMPTED THE UPGRADE TO
A WINTER STORM WARNING THIS MORNING.
PRECIP WILL CLEAR OUT FROM SW TO NE TONIGHT BUT THE RADAR WILL FILL
BACK WITH RAIN AROUND 3-4 AM AS THE COLD FRONT PLOWS THROUGH THE
CASCADES AND CENTRAL WASHINGTON. RELATIVELY LIGHT SOUTHERLY WINDS
WILL QUICKLY BECOME GUSTY SOUTHWEST/WEST WINDS AS THE COLD FRONT
MOVES THROUGH TOMORROW MORNING. THE HREF ENSEMBLE GIVES
SPOKANE/PULLMAN A 20-50% CHANCE OF 50+ MPH WINDS FOR A FEW HOURS IN
THE MORNING/EARLY AFTERNOON WHICH PROMPTED A WIND ADVISORY. THIS
WIND WILL SCOUR OUT THE LOW STRATUS DECK AND LEAD TO SOME NEEDED
SUNSHINE FOR MANY TOMORROW. MODELS SHOW SOME REDEVELOPMENT OF LOW
STRATUS INTO THURSDAY BUT CONFIDENCE IS LOW. DB
THURSDAY THROUGH TUESDAY: THE LONGWAVE PATTERN FEATURES A LOW
PRESSURE TROUGH OVER THE GULF OF ALASKA WITH PERSISTENT SOUTHWEST
FLOW OVER THE INLAND NORTHWEST. THIS WILL KEEP TEMPERATURES MILD
AND SNOW LEVELS RELATIVELY HIGH AND GENERALLY WITH THE RANGE OF
3,000 TO 4,000 FEET. A SERIES OF SHORTWAVE DISTURBANCES WILL PUSH
THROUGH BRINGING ROUNDS OF PRECIPITATION TO THE REGION. A WEAK
DISTURBANCE LOOKS TO MOVE ACROSS SOMETIME BETWEEN THURSDAY NIGHT
AND FRIDAY. MEDIUM RANGE MODELS INDICATE SUBSEQUENT FRONTAL
SYSTEMS PUSHING ACROSS EVERY 24-36 HOURS OR SO OVER THE WEEKEND
INTO NEXT WEEK. EACH LOOK TO BECOME PROGRESSIVELY MORE WET. THERE
ARE INDICATIONS OF AN ATMOSPHERIC RIVER (AR) EVENT AROUND THE
MIDDLE PART OF NEXT WEEK (CHRISTMAS TIME). IMPACTS ASSOCIATED WITH
THIS POTENTIAL WOULD BE THAT OF RAIN AT LOW TO MID ELEVATIONS
WITH MILD TEMPERATURES THAT MAY NOT COOL DOWN BELOW FREEZING
OVERNIGHT. WE DON'T HAVE A LOT OF LOW ELEVATION SNOW TO MELT, BUT
THERE MAY BE SOME CONTRIBUTION ALONG WITH THE RAIN. WE WILL NEED
TO MONITOR THE POTENTIAL FOR HYDROLOGY CONCERNS, BUT THERE IS
STILL A LOT OF UNCERTAINTY ON THE STRENGTH OF A POTENTIAL AR
EVENT. AT THIS TIME, HYDROLOGY IMPACTS LOOK TO BE MINOR. THERE
WILL BE THE POTENTIAL FOR RISES ON RIVERS AND STREAMS WITH
FLASHIER CREEKS AND STREAMS POSSIBLY HAVING THE BEST POTENTIAL FOR
SEEING MINOR FLOODING IMPACTS. SNOW WILL MOST LIKELY BE RESERVED
FOR THE MOUNTAINS, AND COULD BE HEAVY AT TIMES. ANY IMPACTS FROM
SNOW WILL BE AT MOUNTAIN PASSES, AND THE RAIN/SNOW LINE WOULD
LIKELY SHIFT AT TO ABOVE PASS LEVEL DEPENDING ON WHEN THE REGION
IS SITUATED WITHIN THE WARM SECTORS. HIGH TEMPERATURES ARE
GENERALLY EXPECTED TO BE IN THE 40S AND LOWS IN THE 30S OVER THIS
PERIOD. /SVH
AVIATION
18Z TAFS: PRECIPITATION WILL SPREAD ACROSS CENTRAL AND EASTERN
WASHINGTON (AND EVENTUALLY N ID) THRU THE MORNING AND PICK UP IN
INTENSITY THROUGH THE AFTERNOON. THOUGH SNOW FOR MANY LOCATIONS
EARLY, SNOW LEVELS WILL RISE LATER TODAY WITH PRIMARILY RAIN
EXPECTED, THOUGH AREAS OF -FZRA WILL BE POSSIBLE DURING THE
TRANSITION. INCREASING SOUTHWEST WINDS AFTER 09Z WEDNESDAY.
FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: FZRA MENTIONED
FOR KEAT AND HAVE MODERATE CONFIDENCE FOR IT TO OCCUR. THERE IS A
HIGHER CONFIDENCE OF FREEZING RAIN ACROSS THE CASCADES DURING THE
EVENING AND OVERNIGHT.
-----------------------
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 34 46 31 39 32 41 / 90 70 0 0 10 0
COEUR D'ALENE 35 45 31 41 32 43 / 90 80 0 0 10 0
PULLMAN 35 46 31 42 33 44 / 80 80 0 0 10 0
LEWISTON 40 54 34 46 36 48 / 70 40 0 0 0 0
COLVILLE 29 43 24 36 30 40 / 80 80 0 10 20 10
SANDPOINT 33 42 29 37 31 40 / 90 90 0 10 20 10
KELLOGG 35 43 32 42 33 44 / 80 80 0 0 10 10
MOSES LAKE 35 47 30 42 33 43 / 80 20 0 0 10 0
WENATCHEE 33 44 29 37 32 40 / 80 30 0 10 10 0
OMAK 32 44 27 37 32 40 / 90 60 0 10 20 0
OTX WATCHES/WARNINGS/ADVISORIES
ID...WIND ADVISORY FROM 4 AM TO 1 PM PST WEDNESDAY FOR COEUR D'ALENE
AREA-IDAHO PALOUSE.
WA...WIND ADVISORY FROM 4 AM TO 1 PM PST WEDNESDAY FOR LOWER GARFIELD
AND ASOTIN COUNTIES-SPOKANE AREA-UPPER COLUMBIA BASIN-
WASHINGTON PALOUSE-WATERVILLE PLATEAU.
WINTER WEATHER ADVISORY UNTIL 4 AM PST WEDNESDAY FOR CENTRAL
CHELAN COUNTY-OKANOGAN HIGHLANDS-OKANOGAN VALLEY-WATERVILLE
PLATEAU-WENATCHEE AREA-WESTERN OKANOGAN COUNTY.
WINTER STORM WARNING UNTIL 4 AM PST WEDNESDAY FOR WESTERN CHELAN
COUNTY.
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