803
FXUS66 KOTX 171138
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
338 AM PST SUN NOV 17 2024
SYNOPSIS
A WINTER STORM WILL CONTINUE TO BRING SNOW TO THE MOUNTAINS
OVER THE WEEKEND WITH HEAVY SNOW ACCUMULATIONS IMPACTING TRAVEL
ACROSS THE CASCADE CREST AND OVER LOOKOUT PASS. THE WEATHER
PATTERN FOR NEXT WEEK IS TRENDING WETTER WITH POTENTIAL FOR
WIDESPREAD SNOW TUESDAY NIGHT INTO WEDNESDAY THEN RAIN AND SNOW
THROUGH THE REMAINDER OF THE WEEK.
DISCUSSION
TODAY AND TOMORROW: STRONG WARM AIR ADVECTION IS CAUSING A
GRADUAL CHANGEOVER TO ALL RAIN IN EASTERN WASHINGTON AND NORTH
IDAHO THIS MORNING. SURFACE TEMPERATURES HAVE RISEN A COUPLE
DEGREES AND WILL CONTINUE TO RISE EARLY THIS MORNING. THE RADAR IS
STILL TO FILL BACK IN OVER THE PALOUSE AND WILL CONTINUE TO FILL
IN TO THE NORTH AND WEST TOWARDS CENTRAL WASHINGTON IN THE MORNING
AND AFTERNOON HOURS AHEAD OF A FRONTAL PASSAGE. ALL OF THIS WILL
BE RAIN IN THE LOWLANDS AS TEMPERATURES WARM UP INTO THE 40S
RATHER QUICKLY THIS MORNING EXCEPT NEAR THE CANADIAN BORDER. A
STRONG COLD FRONT PASSAGE WILL OCCUR THIS AFTERNOON AND EVENING
WHICH WILL LARGELY SCOUR OUT PRECIPITATION IN THE LOWLANDS.
SNOW WILL CONTINUE IN THE CASCADES AND IDAHO PANHANDLE MOUNTAINS
BEHIND THE FRONT PASSAGE SUNDAY EVENING THROUGH MONDAY THANKS TO A
CONDITIONALLY UNSTABLE AIRMASS AND WESTERLY UPSLOPE FLOW IS IN
PLACE. THERE IS A 20-50% CHANCE OF SNOWFALL RATES GREATER THAN AN
INCH AN HOUR AT STEVENS PASS FROM APPROXIMATELY 2 TO 9 PM AS LAPSE
RATES STEEPEN BEHIND THE COLD FRONT AND A CONVERGENCE ZONE FORMS.
THE EXACT PLACEMENT OF THIS REMAINS UNCERTAIN BUT COULD BRING
VERY CHALLENGING TRAVEL CONDITIONS THIS AFTERNOON AND EVENING AT
STEVENS PASS. CENTRAL AND EASTERN WASHINGTON WILL HAVE A BIT OF A
BREAK IN PRECIPITATION MONDAY DUE STRONG SHADOWING AND LIMITED
ATMOSPHERIC MOISTURE. MODELS SHOW A WEAK SHORTWAVE MOVING IN
CENTRAL WASHINGTON OVERNIGHT INTO TUESDAY WHICH WOULD BRING A
ROUND OF LIGHT SNOW TO CENTRAL AND EASTERN WASHINGTON BEFORE
COMMUTE TIME. TEMPERATURES WOULD BE COOL ENOUGH FOR SNOW
EVERYWHERE MONDAY NIGHT SO THIS WILL NEED TO BE WATCHED CLOSELY.
/DB
...WIDESPREAD SNOW TUESDAY NIGHT INTO WEDNESDAY. SIGNIFICANT
SNOWFALL EXPECTED IN CENTRAL WA...
TUESDAY: WIDELY SCATTERED SNOW SHOWERS WILL BE DRIFTING THROUGH THE
REGION TUESDAY MORNING AND EARLY AFTERNOON AS A COLD UPPER-LEVEL
TROUGH GETS SHOVED TO THE EAST. THE HEAVIEST CONCENTRATION OF
SHOWERS IS EXPECTED FROM THE UPPER COLUMBIA BASIN TO THE CANADIAN
BORDER AND INTO NORTH IDAHO INCLUDING COMMUNITIES LIKE WILBUR,
DAVENPORT, SPOKANE, SANDPOINT, COLVILLE, AND REPUBLIC. THIS
ACTIVITY WILL BE CAPABLE OF A QUICK INCH OF SNOW AND SLICK
CONDITIONS DURING THE TUESDAY MORNING COMMUTE. SHOWER ACTIVITY
WILL WANE IN THE AFTERNOON WITH TEMPERATURES IN THE 30S TO LOWER
40S. WINDS WILL BE LIGHT AND BEGIN SHIFTING TO THE EAST AND
SOUTHEAST DRAWN TO A POWERFUL CYCLONE OFF THE WA COAST.
TUESDAY NIGHT THROUGH WEDNESDAY: AN EXTREMELY INTENSE LOW PRESSURE
OFF THE WA COAST WILL DRAW GUSTY EASTERLY WINDS ACROSS THE INLAND
NW WHILE DEEP MOISTURE STREAMS INLAND ALOFT RESULTING IN A
MODERATE TO HEAVY QPF EVENT FOR AREAS OF CENTRAL AND EASTERN WA.
ANTECEDENT COLD AIR LEFT IN THE WAKE OF TUESDAY'S TROUGH WILL
ALLOW FOR SNOW LEVELS TO BE NEAR VALLEY FLOORS FOR MOST AREAS
OUTSIDE THE DEEP BASIN. THE FOCUS FOR SIGNIFICANT WINTER WEATHER
AND AN ANOMALOUS SNOW EVENT WILL BE OVER CENTRAL WASHINGTON
INCLUDING THE CASCADES, OKANOGAN HIGHLANDS, WATERVILLE PLATEAU,
AND THE ENTIRE HIGHWAY 97 CORRIDOR FROM BLEWETT PASS TO SOUTHERN
BC. LIGHT TO LOCALLY MODERATE SNOW AND TRAVEL IMPACTS WILL EXTEND
EASTWARD INTO THE REMAINDER OF E WA AND NORTH ID BUT THE EVENT
WILL NOT BE OUT OF THE ORDINARY FOR LATE NOVEMBER STANDARDS.
CONFIDENCE IS MODERATE AT THIS TIME WITH THE MAIN CHANGES NOTED IN
THE MODEL GUIDANCE COMING WITH WAVERING IN EXACT QPF AMOUNTS.
IMPACTS: RESIDENTS OF THE INLAND NW SHOULD PLAN FOR A SLOW COMMUTE
COME WEDNESDAY MORNING, ESPECIALLY IN CENTRAL AND NORTHERN WA.
TRAVEL ACROSS THE CASCADE PASSES WILL BE VERY CHALLENGING AND
CONSIDER ADJUSTING TRAVEL TIMES. SNOWFALL RATES OF 1-2" HOUR IN
CENTRAL WA COULD MAKE TRAVEL VERY CHALLENGING AND WE URGE
RESIDENTS TO MAKE SURE YOU HAVE YOUR WINTER SAFETY KIT.
TIMING/SNOW LEVELS: SNOW WILL INCREASE OVER THE CASCADES AROUND SUNSET
TUESDAY EVENING AND SLOWLY EXPAND EAST INTO THE COLUMBIA BASIN
AND OKANOGAN HIGHLANDS AROUND MIDNIGHT THEN ACROSS THE IDAHO
BORDER NEAR THE MORNING COMMUTE. THE HEAVIEST SNOW INTENSITIES
WILL BE THROUGH MIDDAY WEDNESDAY THEN SNOW WILL HAVE THE POTENTIAL
TO PERSIST FOR AREAS NORTH OF I-90 INTO THE THURSDAY AT LIGHTER
INTENSITIES. CONFIDENCE WITH DETAILS TUMBLES AFTER MIDDAY
WEDNESDAY WITH THE AXIS OF MOISTURE DRAPED OVER THE AREA BUT
UNCERTAINTY WITH TIMING AND STRENGTH OF MIDLEVEL WAVES COMING
THROUGH.
ALL BUT THE DEEP BASIN WILL LIKELY START AS SNOW. WARMER AIR NOSING
NORTH/NORTHEASTWARD WEDNESDAY AFTERNOON WILL BRING A TRANSITION
FROM SNOW TO RAIN STARTING IN SOUTHEASTERN WA AND WORKING ITS WAY
EAST AND NORTH WITH TIME. COLD AIR DAMMING IN THE LEE OF THE
CASCADES AND AROUND THE REPUBLIC AREA TO THE CANADIAN BORDER WILL
BE SLOWEST TO SCRUB OUT THE COLD AIR AND HAVE THE POTENTIAL TO
REMAIN SNOW OR WET SNOW THROUGHOUT THE ENTIRE EVENT. FORECAST
FAVORS A SLOWER TRANSITION.
SNOW AMOUNTS: SNOW AMOUNTS ARE PRELIMINARY AND WILL LIKELY CHANGE AS
THE FORECAST BECOMES FINE TUNED. AT THIS TIME, FORECAST IS
CALLING FOR 6-10 INCHES FOR THE VALLEYS OF CENTRAL WA INCLUDING
WENATCHEE, CHELAN, OMAK, WINTHROP, REPUBLIC, AND LEAVENWORTH.
WENATCHEE PROPER CARRIES THE MOST UNCERTAINTY DUE TO A POTENTIAL
FOR MIDLEVEL WINDS TO SHIFT SOUTHERLY QUICKER RESULTING IN
DOWNSLOPING OFF MISSION RIDGE. IF THIS IS DELAYED, IT COULD FALL
ON THE HIGHER END, QUICKER - MORE IN THE 3-6 RANGE. THE MOUNTAINS
WILL BE CLOSER TO A FOOT OR MORE. SNOW AMOUNTS TAPER OFF CLOSER TO
2-5 INCHES FOR THE VALLEYS OF NE WA AND N ID AND 5-10 INCHES IN
THE MOUNTAINS. AMOUNTS ARE LESS THAN 2 INCHES FOR THE LOWER BASIN,
PALOUSE, AND CAMAS PRAIRIE. LESS THAN AN INCH IS EXPECTED IN THE
L-C VALLEY, LA CROSSE, AND SOUTH OF MOSES LAKE.
WINDS: QUITE THE IMPRESSIVE CYCLONE EXPECTED TO DEVELOP 400 MILES OFF
THE WA COAST WITH HURRICANE FORCE WINDS ROTATING AROUND A 950MB
OR LOWER CENTER. THIS WILL DRAW GUSTY EAST WINDS ACROSS OUR NECK
OF THE WOODS WITH SPEEDS OF 10-20 MPH AND GUSTS TO 30 MPH. LOCALLY
STRONGER WINDS WILL BE FOUND CHANNELING THROUGH THE CASCADE
RIDGES AND PASSES WHICH COULD GUST UPWARDS OF 50 MPH. LOCALLY
STRONGER WINDS WILL ALSO BE POSSIBLE IN THE IMMEDIATE LEE OF THE
BLUE MOUNTAINS AND UP THE SNAKE RIVER VALLEY DUE TO TERRAIN
CHANNELING/MOUNTAIN WAVES. THIS AREA WILL NEED TO BE MONITORED FOR
WIND GUSTS OF 40 MPH OR STRONGER.
THURSDAY THROUGH SUNDAY: THURSDAY THROUGH SATURDAY: THERE IS AN 90%
CHANCE FOR AN UNSETTLED WEATHER PATTERN TO PERSIST THROUGHOUT THE
WEEK WITH A PLUME OF MOISTURE WAVERING NORTH AND SOUTH AND
FRONTAL WAVES PASSING THROUGH. SNOW LEVELS WILL CONTINUE TO RISE
WITH TIME WITH PRIMARILY RAIN IN THE LOWLANDS AND SNOW IN THE
MOUNTAINS. THE AREA CARRYING THE HIGHEST UNCERTAINTY WILL BE THE
METHOW VALLEY AND VALLEYS TUCKED ALONG THE CANADIAN BORDER. COOLER
AIR MAY STRUGGLE TO FULLY SCRUB OUT WITH ADDITIONAL SNOW. WE DO
NOT SEE A MORE WIDESPREAD COOLING OF THE AIR MASS UNTIL SUNDAY
WHEN A LARGER TROUGH EJECTS INLAND. AS SUCH, TEMPERATURES WILL
TREND NEAR TO WARMER THAN NORMAL WITH LOW PROBABILITIES FOR
FREEZING TEMPERATURES OVERNIGHT UNTIL THE WEEKEND. /SB
AVIATION
06Z TAFS: WINTER STORM SYSTEM BRINGING RAIN AND SNOW TO AVIATION
AREA ALLOWING FOR LIFR/IFR CONDITIONS TO PREVAIL FOR LOCATIONS
NEAR KGEG AND VICINITY BETWEEN NOW AND 10Z WITH SOME TENDENCY TO
RAISE TO IFR/MVFR AFTERWARD. LOW LEVEL WIND SHEAR A GOOD
POSSIBILITY AS THE BACK EDGE OF THE SYSTEM MOVES THROUGH AS A COLD
FRONT WITH SURFACE GUSTS TO 40KTS A POSSIBILITY WITH PREVAILING
WIND DIRECTION FROM THE SOUTHWEST. /PELATTI
FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
CONFIDENCE IS HIGH FOR IFR CONDITIONS WITH THE WINTER STORM
OVERNIGHT INTO SUNDAY FOR KGEG-KSFF-KCOE. THE STRATIFORM NATURE OF
THE PRECIPITATION IS TYPICALLY WELL HANDLED BY MODEL 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 46 30 40 26 39 29 / 80 70 30 20 40 60
COEUR D'ALENE 43 31 39 25 37 26 / 90 90 50 50 50 50
PULLMAN 42 30 38 25 37 29 / 100 90 50 40 20 60
LEWISTON 49 34 45 29 43 32 / 80 50 30 20 10 50
COLVILLE 44 22 38 18 35 24 / 40 20 30 20 40 60
SANDPOINT 41 30 36 24 34 22 / 90 90 80 60 60 50
KELLOGG 40 30 35 27 36 23 / 90 90 90 70 50 50
MOSES LAKE 50 29 45 24 42 33 / 50 20 0 20 20 90
WENATCHEE 48 30 44 27 37 30 / 30 10 0 20 30 100
OMAK 46 25 42 23 39 29 / 10 10 0 20 20 90
OTX WATCHES/WARNINGS/ADVISORIES
ID...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR IDAHO
PALOUSE-NORTHERN PANHANDLE.
WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR CENTRAL
PANHANDLE MOUNTAINS.
WA...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR
NORTHEAST MOUNTAINS-OKANOGAN HIGHLANDS.
WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR WESTERN CHELAN
COUNTY-WESTERN OKANOGAN COUNTY.
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