189
FXUS66 KSTO 192112
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
112 PM PST TUE NOV 19 2024
SYNOPSIS
A STRONG ATMOSPHERIC RIVER STORM BRINGS PERIODS OF MODERATE TO HEAVY
RAIN AND MOUNTAIN SNOW, ISOLATED THUNDERSTORMS, AND GUSTY SOUTHERLY
WINDS TO INTERIOR NORCAL THROUGH THE END OF THE WEEK AND INTO THE
WEEKEND.
*WINTER STORM WARNING: 4 PM TODAY THROUGH 10 PM WEDNESDAY FOR
ELEVATIONS ABOVE 3500 FEET ALONG THE
SIERRA/SOUTHERN CASCADES, COASTAL RANGE,
AND ABOVE 3000 FEET IN THE SHASTA COUNTY
MOUNTAINS.
*FLOOD WATCH: 10 PM TONIGHT THROUGH 4 AM SATURDAY FOR
VALLEY/FOOTHILLS LOCATIONS GENERALLY
NORTH INTERSTATE 80 AND BELOW 3000 FEET.
*WIND ADVISORY: 10 PM TONIGHT THROUGH 4 PM WEDNESDAY FOR
THE NORTHERN/CENTRAL SACRAMENTO VALLEY
AND NORTHEAST FOOTHILLS.
DISCUSSION
LATEST GOES-WEST SATELLITE IMAGERY THIS AFTERNOON DEPICTS MOSTLY
CLOUDY SKIES OVERTAKING INTERIOR NORCAL AS A ROBUST TROUGH
APPROACHES THE PACIFIC NORTHWEST COASTLINE. WHILE SOME LIGHT RADAR
RETURNS ARE BEGINNING TO SHOW UP ACROSS SHASTA AND TEHAMA
COUNTIES, NO ACCUMULATING PRECIPITATION HAS BEEN OBSERVED AS OF 12
PM PST. OTHERWISE, WINDS CURRENTLY REMAIN LIGHT TO BREEZY OUT OF
THE SOUTH-SOUTHEAST, WITH CURRENT TEMPERATURES RUNNING ABOUT 5 TO
10 DEGREES COOLER THAN THIS TIME YESTERDAY. PRECIPITATION CHANCES
WILL CONTINUE TO INCREASE THROUGH THE AFTERNOON AND EVENING, WITH
HIGHEST IMPACTS EXPECTED GENERALLY NORTH OF INTERSTATE 80.
AS THE AFOREMENTIONED TROUGH CONTINUES TO NEAR THE PACIFIC
NORTHWEST COAST, PRECIPITATION CHANCES LOOK TO SPREAD FURTHER
SOUTHWARD, WITH INCREASING PRECIPITATION INTENSITY FURTHER
NORTHWARD. ADDITIONALLY, SOUTHERLY WINDS ARE EXPECTED TO BECOME
GUSTY THIS EVENING INTO WEDNESDAY. STRONGEST LOWER ELEVATION WIND
GUSTS 35 TO 45 MPH ARE ANTICIPATED ACROSS THE NORTHERN/CENTRAL
SACRAMENTO VALLEY, WITH GUSTS 25 TO 35 MPH ELSEWHERE. ALONG THE
SIERRA, GUSTS TO 55 MPH WILL BE POSSIBLE AS WELL. HEAVIEST
PRECIPITATION WITH THIS INITIAL WAVE IS CURRENTLY EXPECTED TO
PERIODICALLY FALL THROUGH FRIDAY MORNING, WITH COMPARATIVELY
LIGHTER PRECIPITATION THEN ANTICIPATED THROUGH SATURDAY MORNING.
ALTHOUGH, HIGHEST THUNDERSTORM POTENTIAL (10% TO 20% ACROSS THE
VALLEY/FOOTHILLS) IS EXPECTED FRIDAY EVENING INTO SATURDAY AS THE
TROUGH EVENTUALLY TRAVELS INLAND.
RESULTANT FORECAST PRECIPITATION TOTALS THROUGH SATURDAY MORNING
CONTINUE TO FAVOR ACCUMULATIONS OF 7 TO 10 INCHES AT HIGH
ELEVATIONS NORTH OF INTERSTATE 80, 3 TO 6 INCHES FOR
VALLEY/FOOTHILLS LOCATIONS NORTH OF INTERSTATE 80, AND 1 TO 3
INCHES ELSEWHERE. AS A RESULT, PROBABILITIES OF EXCEEDING 3" OF
PRECIPITATION ARE AROUND 40% TO 70% FOR LOCATIONS FROM INTERSTATE
80 SOUTHWARD, WITH 70% TO 90% PROBABILITIES FOR LOCATIONS
GENERALLY NORTH OF INTERSTATE 80.
AS THIS TROUGH PROGRESSES AND RETROGRADES WESTWARD FROM THE
PACIFIC NORTHWEST COAST, SNOW LEVELS ARE EXPECTED TO FLUCTUATE
THROUGH THE REMAINDER OF THE WEEK. INITIAL SNOW LEVELS THROUGH
TODAY AND INTO WEDNESDAY MORNING ARE EXPECTED TO SIT AROUND 3000
TO 4000 FEET, BEFORE RISING TO 4000 TO 5500 FEET BY WEDNESDAY
AFTERNOON, THEN 7000 TO 8000 FEET THURSDAY INTO FRIDAY. LOWEST
SNOW LEVELS DOWN TO 3000 FEET ARE EXPECTED TO REMAIN CONFINED TO
THE SHASTA COUNTY MOUNTAINS. FORECAST SNOWFALL ACCUMULATIONS OF 10
TO 20 INCHES WILL BE POSSIBLE THROUGH SATURDAY MORNING AT
ELEVATIONS ABOVE 4500 FEET, WITH ACCUMULATIONS 5 TO 10 INCHES DOWN
TO AROUND 3500 FEET ALONG THE SIERRA AND DOWN TO AROUND 3000 FEET
ACROSS THE SHASTA COUNTY MOUNTAINS. LOCALLY HIGHER TOTALS OF 2 TO
4 FEET WILL BE POSSIBLE OVER PEAKS AS WELL. RESULTANT
PROBABILITIES OF SNOWFALL EXCEEDING 1 FOOT ARE AROUND 30% TO 70%
ABOVE 4500', WITH 30% TO 60% PROBABILITIES OF EXCEEDING 6 INCHES
OF SNOWFALL BETWEEN 3000 AND 4500 FEET.
EXTENDED DISCUSSION (SATURDAY THROUGH TUESDAY)
WHILE UNCERTAINTY IN EXACT DETAILS, PARTICULARLY CONCERNING
PRECIPITATION TOTALS, REMAINS HIGH THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK, ENSEMBLE GUIDANCE CONTINUES TO SHOW GOOD
AGREEMENT REGARDING THE EVENTUAL PROGRESSION OF THE TROUGH. THIS
PROGRESSION DOES INCLUDE A POTENTIAL, BRIEF 6 TO 12 HOUR LULL IN
PRECIPITATION ON SATURDAY, ALTHOUGH THERE IS SOME VARIANCE
REGARDING EXACT TIMING OF THIS LULL. REGARDLESS, THE TROUGH IS
EXPECTED TO BEGIN A GRADUAL EASTWARD/ONSHORE PROGRESSION LATE
SATURDAY INTO EARLY NEXT WEEK. DESPITE THIS EXPECTED EASTWARD
PROGRESSION, AMPLIFIED RIDGING OVER THE CENTRAL CONUS LOOKS TO
BROADEN TOWARD THE EASTERN CONUS INTO NEXT WEEK, LEADING TO A VERY
GRADUAL EJECTION OF THE TROUGH. CURRENT ENSEMBLE GUIDANCE DOES
INDICATE A WEAKENING TREND OF THE TROUGH AS IT MOVES ONSHORE,
HINTING AT GENERALLY LIGHTER, BUT MORE WIDESPREAD PRECIPITATION
WITH THE SECOND WAVE.
AS A RESULT, THE NEXT WAVE OF PRECIPITATION IMPACTS IS EXPECTED
TO ARRIVE BY SATURDAY NIGHT AND MAY LINGER AS LATE AS TUESDAY
MORNING. CURRENT PROBABILITIES OF EXCEEDING 1 INCH OF
PRECIPITATION THROUGH TUESDAY MORNING SIT AROUND 50% TO 80% ACROSS
MOST VALLEY/FOOTHILLS LOCATIONS, JUMPING TO 70% TO 90%
PROBABILITIES ALONG THE SIERRA AND INTO THE NORTHERN SACRAMENTO
VALLEY. GIVEN THE EXPECTED LATE WEEK STALL OVER THE PACIFIC AND
THE SLIGHT WEAKENING OF THE SYSTEM AS IT MOVES ONSHORE, SNOW
LEVELS LOOK TO DROP TO AROUND 4000 TO 5000 FEET BY SUNDAY MORNING
AND GENERALLY STABILIZE THERE INTO EARLY NEXT WEEK. ATTENDANT
PROBABILITIES OF SNOWFALL EXCEEDING 1 FOOT ARE AROUND 60% TO 90%
FOR ELEVATIONS ABOVE 5500 FEET ALONG THE SIERRA, WITH 40% TO 80%
PROBABILITIES OF EXCEEDING 6 INCHES OF SNOWFALL BETWEEN 4000 AND
5500 FEET.
WITH THE ACTIVE WEATHER IN THE FORECAST THIS WEEK, BE SURE TO
STAY UP TO DATE WITH THE LATEST FORECAST AT WEATHER.GOV/STO AND
CHECK CURRENT ROAD CONDITIONS AT QUICKMAP.DOT.CA.GOV BEFORE
TRAVELING!
AVIATION
GENERALLY VFR CONDITIONS EXPECTED FOR MOST INTERIOR NORCAL
LOCATIONS THROUGH 12Z WEDNESDAY. ALTHOUGH, SOME MVFR/IFR
INTRODUCTION IS EXPECTED BY 10Z AT RDD AND RBL AND SURROUNDING
TERRAIN AS A PROLONGED WEATHER SYSTEM STARTS TO IMPACT THE REGION.
SOUTH-SOUTHEAST WINDS GENERALLY 12 KTS OR LESS ANTICIPATED
THROUGH 06Z, BECOMING GUSTY OVERNIGHT INTO WEDNESDAY. GUSTS 20 TO
30 KTS EXPECTED FOR THE DELTA, VALLEY, AND FOOTHILLS, WITH GUSTS
40 TO 50 KTS ALONG THE SIERRA. SOME LLWS ALSO POSSIBLE AT RDD
AFTER 05Z.
STO WATCHES/WARNINGS/ADVISORIES
WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 10 PM PST
WEDNESDAY FOR MOUNTAINS SOUTHWESTERN SHASTA COUNTY TO WESTERN
COLUSA COUNTY-SHASTA LAKE AREA / NORTHERN SHASTA COUNTY-WEST
SLOPE NORTHERN SIERRA NEVADA-WESTERN PLUMAS COUNTY/LASSEN PARK.
FLOOD WATCH FROM 10 PM PST THIS EVENING THROUGH LATE FRIDAY
NIGHT FOR CENTRAL SACRAMENTO VALLEY-MOUNTAINS SOUTHWESTERN
SHASTA COUNTY TO WESTERN COLUSA COUNTY-NORTHEAST
FOOTHILLS/SACRAMENTO VALLEY-NORTHERN SACRAMENTO VALLEY-SHASTA
LAKE AREA / NORTHERN SHASTA COUNTY.
WIND ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST WEDNESDAY FOR
CENTRAL SACRAMENTO VALLEY-NORTHEAST FOOTHILLS/SACRAMENTO VALLEY-
NORTHERN SACRAMENTO VALLEY.
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