346
FXUS66 KOTX 182340
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
340 PM PST MON NOV 18 2024
SYNOPSIS
PRECIPITATION WILL BE MORE SHOWERY THROUGH EARLY TUESDAY. WEATHER
WILL REMAIN UNSETTLED THROUGH THE WEEK WITH THE NEXT WINTER STORM
TUESDAY NIGHT INTO WEDNESDAY BRINGING ANOTHER ROUND OF WIDESPREAD
SNOW. THIS WILL RESULT IN MODERATE TO MAJOR IMPACTS ACROSS
CENTRAL WASHINGTON AND MINOR IMPACTS FOR EASTERN WASHINGTON AND
NORTH IDAHO. ADDITIONAL SYSTEMS PASSING THROUGH THURSDAY THROUGH
NEXT WEEKEND WILL BRING ADDITIONAL PERIODS OF LOWLAND RAIN AND
MOUNTAIN SNOW.
DISCUSSION
TONIGHT AND TUESDAY: THE INLAND NW IS IN A CONDITIONALLY UNSTABLE
AIR MASS THROUGH TUESDAY MORNING WITH 500MB TEMPERATURES DOWN TO
35C LEADING TO STEEP MID LEVEL LAPSE RATES. THIS WILL RESULT IN
CONTINUED SHOWER ACTIVITY OVER THE REGION, WITH THE HIGHEST
COVERAGE ALONG THE CASCADE CREST, AND IDAHO PANHANDLE WITH THE
ASSISTANCE OF LOW LEVEL UPSLOPE FLOW. ALTHOUGH SNOW LEVELS WILL BE
FALLING OVERNIGHT DOWN TO THE VALLEY FLOORS SO ANY SHOWERS
OVERNIGHT INTO TUESDAY MORNING WILL HAVE THE POTENTIAL TO PRODUCE
SLICK ROADS. TUESDAY AFTERNOON A BRIEF SHORT WAVE RIDGE MOVES OVER
THE REGION AHEAD OF A STRONG WEATHER SYSTEM. JW
..HEAVY SNOW TO IMPACT CENTRAL WA TUESDAY NIGHT INTO WEDNESDAY
TUESDAY NIGHT THROUGH WEDNESDAY: MODELS CONTINUE TO REMAIN IN GOOD
AGREEMENT IN A LOW PRESSURE UNDERGOING EXPLOSIVE CYCLOGENESIS AS
IT NEARS THE WASHINGTON COAST ON TUESDAY AND AMPLIFIES AN UPPER
LEVEL RIDGE OVER THE INTERIOR WESTERN US. DEEP SOUTHWEST FLOW
ALOFT WILL ALLOW AN ATMOSPHERIC RIVER TO TAKE AIM AT NORTHERN
CALIFORNIA AND SOUTHWESTERN OREGON TUESDAY NIGHT. AS THIS LOW
BEGINS TO OCCLUDE TUESDAY NIGHT AND GRADUALLY SHIFTS NORTHWESTWARD,
IT WILL DRAW WARM, MOIST AIR INTO EASTERN WASHINGTON AND NORTH
IDAHO, RESULTING IN WIDESPREAD MODERATE TO HEAVY PRECIPITATION.
THE SURFACE LOOKS TO START OFF QUITE DRY AND COLD TUESDAY EVENING
WITH DEW POINTS IN THE LOW TO MID 20S WHICH WILL LEAD TO SOME
COOLING AS THE COLUMN SATURATES FROM THE TOP DOWN. THE FOCUS FOR
AN ANOMALOUS SNOW EVENT WILL FOR THE CASCADES, THE EAST SLOPES,
THE WATERVILLE PLATEAU, OKANOGAN VALLEY AND HIGHLANDS AS A STRONG
EAST TO SOUTHEAST PRESSURE GRADIENT OF -14 TO 18 MB FROM SEA-GEG
WILL PROVIDE FAVORABLE UPSLOPE FLOW INTO THESE AREAS. THIS IS
CONSISTENT WITH THE ECMWF EXTREME FORECAST INDEX WHICH HIGHLIGHTS
THESE AREAS FOR AN ANOMALOUS SNOW EVENT TUESDAY NIGHT INTO
WEDNESDAY MORNING. PRECIPITATION WILL FALL AS SNOW ACROSS THE
UPPER COLUMBIA BASIN, NORTHEAST WASHINGTON, PALOUSE, SPOKANE AREA,
AND THE IDAHO PANHANDLE LATER TUESDAY EVENING THROUGH EARLY
WEDNESDAY MORNING. WHILE THIS WILL PROVIDE THE MOST SNOW SOME OF
THESE LOWLAND AREAS HAVE SEEN SO FAR THIS YEAR, IT IS NOT BEING
HIGHLIGHTED AS PARTICULARLY ABNORMAL.
SNOW AMOUNTS: SNOW WILL INCREASE OVER THE CASCADES AND CENTRAL
WASHINGTON TUESDAY EVENING. STRONG UPSLOPE AND ISENTROPIC ASCENT
INTO THE EAST SLOPES SUGGEST PERIODS OF MODERATE TO HEAVY
SNOWFALL RATES FOR THESE AREAS BETWEEN 10 PM AND 4 AM. SNOWFALL
WILL SPREAD NORTHEAST INTO FAR EASTERN WASHINGTON AND THE IDAHO
PANHANDLE LATE TUESDAY NIGHT. AT THIS TIME, OUR FORECAST IS
CALLING FOR 6 TO 10 INCHES OF SNOW FOR THE CENTRAL WASHINGTON
VALLEYS AND 10 TO 15 INCHES FOR STEVENS, WASHINGTON, SHERMAN, AND
BLEWETT PASSES. THERE STILL REMAINS UNCERTAINTY IN THE EXACT
AMOUNTS FOR THE WENATCHEE AREA AS THE WINDS SHIFT TO THE SOUTH
WEDNESDAY MORNING. MOST DETERMINISTIC MODELS WANT HAVE 850MB WINDS
SHIFTING TO THE SOUTH-SOUTHEAST AFTER 10AM WEDNESDAY WITH
DOWNSLOPING WINDS OFF MISSION RIDGE ENDING THE PRECIPITATION,
HOWEVER THE GFS WANTS TO HOLD ON TO THE SOUTHEAST FLOW INTO
CENTRAL WA LONGER.
FURTHER EAST INTO THE SPOKANE AND COEUR D’ALENE AREAS, AMOUNTS
LOOK TO BE MUCH LESS COMPARED TO CENTRAL WASHINGTON, BUT MODELS
ARE SUGGESTING A 3 TO 5 HOUR PERIOD OF MODERATE SNOW RATES EARLY
WEDNESDAY MORNING BEFORE SWITCHING OVER TO RAIN. THERE ARE SOME
TIMING DIFFERENCES IN THE HIGH RESOLUTION MODELS THAT ARE
AVAILABLE WHEN THIS BAND WILL MOVE THROUGH WITH THE HRRR HAVING
THE BAND OVER THE SPOKANE AREA AROUND 1AM AND TRANSITIONING TO
RAIN BY 4AM. ON THE OTHER HAND, THE NAMNEST DELAYS THE SNOW OVER
THE SPOKANE AREA UNTIL 4-5AM. WITH THAT SAID, THE DELAYED START
TIME WOULD RESULT IN A SLICK DRIVE WEDNESDAY MORNING. WARM AIR
NOSING NORTH/NORTHEASTWARD WEDNESDAY MORNING WILL BRING A
TRANSITION FROM SNOW TO RAIN STARTING IN SOUTHEASTERN WASHINGTON
AND WORKING ITS WAY EAST AND NORTH WITH TIME. WINTER WEATHER
ADVISORIES HAVE BEEN ISSUED FOR THE LOWLAND AREAS WHERE 2 TO 4
INCHES OF SNOW ARE EXPECTED GENERALLY ALONG AREAS NORTH OF I-90
FROM THE BASIN THROUGH THE COEUR D'ALENE AREA. FURTHER NORTH
ACROSS THE NORTHEAST VALLEYS AND NORTHERN PANHANDLE VALLEYS LOOK
TO PICK UP BETWEEN 3 AND 6 INCHES. AREAS SOUTH OF I-90 WILL
GENERALLY BE LESS AS THE WARM AIR RESULTS IN A QUICKER TRANSITION
TO RAIN. AROUND MOSES LAKE, SNOW AMOUNTS WILL BE TRICKIER WITH
AREAS SUCH AS QUINCY AND SOAP LAKE WILL HOLD ON TO COLDER AIR
LONGER WITH 2 TO 4 INCHES OF SNOW FORECASTED BUT AREAS FURTHER
SOUTH WILL SEE LESS THAN 1 INCH.
WINDS: THE STRONG EAST TO SOUTHEAST PRESSURE GRADIENT DRAPED
ACROSS THE PACIFIC NORTHWEST WILL RESULT IN GUSTY WINDS FOR THE
CASCADES, THE UPPER COLUMBIA BASIN, THE PALOUSE, L-C VALLEY, AND
THE BLUES. RIDGES IN THE CASCADES HAVE A 50 TO 70 PERCENT CHANCE
OF WIND GUSTS ABOVE 45 MPH TUESDAY NIGHT AND EARLY WEDNESDAY.
PARTICULARLY OVER THE CASCADES, A BLIZZARD WARNING HAS BEEN ISSUED
FOR THE STEVENS PASS AREA WHERE STRONG WINDS AND SNOW WILL RESULT
IN SIGNIFICANT VISIBILITY REDUCTIONS ALONG US 2. /VMT
THURSDAY NIGHT THROUGH MONDAY: A LARGE CLOSED LOW CONTINUES TO
SPIN OFF THE WA/OR COAST THURSDAY NIGHT BEFORE MOVING NORTHEAST TO
JUST OFF VANCOUVER ISLAND FRIDAY INTO SATURDAY. THE CONTINUED
SOUTHWEST FLOW WILL SEND ADDITIONAL ROUNDS OF PRECIPITATION INTO
THE REGION. THE THURSDAY NIGHT/FRIDAY TIME FRAME HAS THE POTENTIAL
TO BE ESPECIALLY WET WITH PRECIPITABLE WATER VALUES INCREASING TO
200-250% OF NORMAL. ENSEMBLE MEANS ARE CURRENTLY PROJECTING AROUND
0.40-1.00" OF PRECIPITATION, MOSTLY IN THE FORM OF VALLEY RAIN AND
MOUNTAIN SNOW. THE NBM IS PROJECTING SNOW LEVELS OF 3500-4500 FEET
ALONG THE EAST SLOPES OF THE CASCADES AND UP NEAR THE CANADIAN
BORDER WHILE AT 6000-7000 FEET OVER SE WASHINGTON INTO THE CENTRAL
PANHANDLE MOUNTAINS. THE INCREASED SNOW LEVELS, RAIN, AND LOW TO
MID ELEVATION SNOW MELT WILL CONTRIBUTE TO INCREASED WATER INTO
AREA RIVERS AND STREAMS. NO FLOODING IS FORECAST AT THIS TIME BUT
THIS WILL CONTINUE TO BE MONITORED. OVER THE WEEKEND INTO EARLY
NEXT WEEK THE TROUGH FINALLY BEGINS TO MOVE INLAND. AS IT DOES SO
PRECIPITATION CHANCES CONTINUE, WITH SNOW LEVELS SUNDAY INTO
MONDAY FALLING AS LOW AS 1500-2500 FEET. JW
AVIATION
00Z TAFS: A CONDITIONALLY UNSTABLE AIR MASS WILL CONTINUE INTO
TUESDAY MORNING RESULTING IN SHOWERS MAINLY OVER THE CASCADES,
AND EASTERN THIRD OF WA/N IDAHO WITH THE ASSISTANCE OF UPSLOPE
FLOW. MOST OF THESE SHOWERS ARE SCATTERED IN NATURE WITH A PROB30
GROUP UTILIZED. TONIGHT AS BOUNDARY LAYER WINDS SHIFT TO SOUTH-
SOUTHEAST A RESURGENCE OF STRATUS IS EXPECTED OVER THE NORTHERN
VALLEYS INCLUDING KGEG/KSFF/KCOE WITH A MIX OF IFR/MVFR CIGS. AS
SOUTH-SOUTHEAST BOUNDARY LAYER WINDS INTENSITY FURTHER WITH A DEEP
APPROACHING SYSTEM TUESDAY AFTERNOON THAT SHOULD HELP CLEAR THE
STRATUS OUT OF THE SPOKANE/COEUR D'ALENE AREAS. A BAND OF SNOW
WILL TRACK ACROSS THE REGION TUESDAY NIGHT INTO WEDNESDAY MORNING
WITH WIDESPREAD LOWLAND ACCUMULATIONS EXPECTED (EXCEPT LEWISTON).
JW
FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
HREF INDICATES AROUND A 70% CHANCE OF CIGS DROPPING BACK DOWN TO
IFR/MVFR FOR KGEG/KSFF OVERNIGHT INTO TUESDAY MORNING, WITH A 40%
CHANCE FOR KMWH STARTING NEAR 15Z TUE. 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 26 37 29 40 31 41 / 20 20 60 90 60 40
COEUR D'ALENE 26 37 26 39 31 42 / 50 30 30 80 80 40
PULLMAN 24 38 29 40 33 42 / 40 30 70 80 60 60
LEWISTON 30 43 32 48 38 48 / 20 10 60 60 30 50
COLVILLE 18 34 24 35 25 39 / 20 30 30 90 70 40
SANDPOINT 24 34 22 35 29 39 / 60 50 20 100 90 50
KELLOGG 26 35 23 39 34 41 / 70 40 20 90 90 70
MOSES LAKE 25 40 33 46 33 44 / 10 20 90 70 40 50
WENATCHEE 28 36 30 39 33 40 / 10 30 100 60 20 40
OMAK 24 35 29 38 31 42 / 10 20 80 90 40 30
OTX WATCHES/WARNINGS/ADVISORIES
ID...WINTER WEATHER ADVISORY FROM MIDNIGHT TUESDAY NIGHT TO 10 PM PST
WEDNESDAY FOR NORTHERN PANHANDLE.
WINTER WEATHER ADVISORY FROM 10 PM TUESDAY TO 10 AM PST
WEDNESDAY FOR COEUR D'ALENE AREA-IDAHO PALOUSE.
WINTER WEATHER ADVISORY UNTIL 6 PM PST THIS EVENING FOR CENTRAL
PANHANDLE MOUNTAINS.
WA...WINTER WEATHER ADVISORY FROM MIDNIGHT TUESDAY NIGHT TO 10 PM PST
WEDNESDAY FOR NORTHEAST MOUNTAINS.
WINTER WEATHER ADVISORY FROM 10 PM TUESDAY TO 10 AM PST
WEDNESDAY FOR SPOKANE AREA-UPPER COLUMBIA BASIN-WASHINGTON
PALOUSE.
WINTER STORM WARNING FROM 10 PM TUESDAY TO 4 PM PST WEDNESDAY
FOR OKANOGAN HIGHLANDS-OKANOGAN VALLEY.
WINTER STORM WARNING FROM 4 PM TUESDAY TO 10 AM PST WEDNESDAY
FOR CENTRAL CHELAN COUNTY-WATERVILLE PLATEAU-WENATCHEE AREA.
WINTER STORM WARNING UNTIL 4 PM PST THIS AFTERNOON FOR WESTERN
CHELAN COUNTY.
BLIZZARD WARNING FROM 4 PM TUESDAY TO 10 AM PST WEDNESDAY FOR
WESTERN CHELAN COUNTY.
WINTER STORM WARNING FROM 4 PM TUESDAY TO 4 PM PST WEDNESDAY FOR
WESTERN OKANOGAN COUNTY.
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