240
FXUS66 KSTO 182221
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
221 PM PST MON NOV 18 2024
SYNOPSIS
WITH A BRIEF LULL IN ACTIVITY TODAY, TEMPERATURES TREND COLD
OVERNIGHT INTO TUESDAY MORNING, WITH WIDESPREAD, LOW ELEVATION
FROST POSSIBLE. PRECIPITATION CHANCES THEN RAPIDLY RETURN TO THE
REGION BY MIDDAY TUESDAY, WITH PERIODS OF MODERATE TO HEAVY
PRECIPITATION THEN EXPECTED THROUGH THE END OF THE WEEK AND INTO
THE WEEKEND.
*FREEZE WARNING: 10 PM TONIGHT THROUGH 10 AM TUESDAY MORNING
FOR ELEVATIONS BELOW 2000 FEET.
*COLD WEATHER ADVISORY: 10 PM TONIGHT THROUGH 10 AM TUESDAY
MORNING FOR ELEVATIONS ABOVE 6000 FEET ALONG
THE SIERRA.
*WINTER STORM WARNING: 4 PM TUESDAY THROUGH 10 PM WEDNESDAY FOR
ELEVATIONS ABOVE 3500 FEET ALONG THE SIERRA/
SOUTHERN CASCADES, COASTAL RANGE, AND SHASTA
COUNTY MOUNTAINS.
*FLOOD WATCH: 10 PM TUESDAY THROUGH 4 AM SATURDAY FOR
VALLEY/FOOTHILLS LOCATIONS GENERALLY NORTH
INTERSTATE 80 AND BELOW 3000 FEET.
DISCUSSION
AS OF EARLY THIS AFTERNOON, MOSTLY TO PARTLY SUNNY SKIES ARE EVIDENT
ACROSS INTERIOR NORCAL VIA LATEST GOES-WEST SATELLITE IMAGERY AS
TRANSIENT RIDGING ALOFT BETWEEN SYSTEMS BUILDS IN. DESPITE MORE
PLENTIFUL SUNSHINE TODAY, BREEZY NORTH WINDS WILL KEEP TEMPERATURES
SLIGHTLY BELOW NORMAL TODAY, WITH MID 50S TO LOW 60S ACROSS THE
DELTA, VALLEY, AND FOOTHILLS, AND 30S TO 40S AT HIGHER ELEVATIONS.
AS WINDS LESSEN THIS EVENING AND SKIES REMAIN MOSTLY CLEAR
OVERNIGHT, LOW TEMPERATURES BY TUESDAY MORNING LOOK TO DROP TO THE
LOW TO MID 30S ACROSS THE DELTA, VALLEY, AND FOOTHILLS, WITH
TEMPERATURES 5 TO 25 DEGREES AT HIGHER ELEVATIONS. AS A RESULT, COLD
WEATHER IMPACTS ARE EXPECTED AT HIGH ELEVATIONS, WITH WIDESPREAD,
LOW ELEVATION FROST ANTICIPATED AS WELL.
ENSEMBLE GUIDANCE CONTINUES TO SHOW INCREASING CONFIDENCE IN THE
EVOLUTION OF A TROUGH DIGGING SOUTHWARD FROM THE GULF OF ALASKA MID
TO LATE WEEK. CURRENT CONSENSUS HAS THE TROUGH APPROACHING THE
PACIFIC NORTHWEST COAST ON TUESDAY, WITH ATTENDANT PRECIPITATION
IMPACTS BEGINNING ACROSS NORTHERN PORTIONS OF THE FORECAST AREA BY
TUESDAY AFTERNOON/EVENING. AS THIS TROUGH IS EXPECTED TO RAPIDLY
DEEPEN AS IT NEARS THE COAST, HEAVIEST PRECIPITATION AND
STRONGEST WINDS WITH THIS INITIAL WAVE ARE EXPECTED OVERNIGHT
TUESDAY INTO WEDNESDAY, ALTHOUGH ADDITIONAL PERIODS OF MODERATE TO
HEAVY PRECIPITATION ARE EXPECTED TO PERSIST THROUGH THE END OF
THE WEEK AS WELL. AS BROAD RIDGING AMPLIFIES ACROSS THE
INTERMOUNTAIN WEST THROUGH THE MIDDLE OF THE WEEK, THE PACIFIC
NORTHWEST TROUGH IS EXPECTED TO STALL AND BRIEFLY RETROGRADE
WESTWARD INTO THURSDAY. WHILE PRECIPITATION STILL LOOKS TO PERSIST
AS THIS OCCURS, A BRIEF PERIOD OF COMPARATIVELY LIGHTER
PRECIPITATION MAY BE POSSIBLE MIDDAY THURSDAY INTO FRIDAY MORNING.
AS THE PRECIPITATION LOOKS TO ARRIVE IN A FEW DIFFERENT WAVES, THE
INITIAL WAVE IS EXPECTED WITH THE TROUGH REMAINING OFFSHORE,
PROVIDING A FAVORABLE FETCH FOR MOISTURE ADVECTION INTO NORCAL ALONG
WITH AMPLE FORCING. CURRENT PRECIPITATION FORECASTS FROM MIDDAY
TUESDAY THROUGH FRIDAY MORNING INDICATE RAINFALL OF 3 TO 6 INCHES
POSSIBLE ACROSS THE VALLEY AND FOOTHILLS NORTH OF INTERSTATE 80,
WITH SOME POTENTIAL FOR PRECIPITATION ACCUMULATIONS UP TO 8 INCHES
WITHIN THE FOOTHILLS AS WELL. FROM INTERSTATE 80 SOUTHWARD,
PRECIPITATION ACCUMULATIONS DROP OFF TO 0.5 TO 2 INCHES POSSIBLE,
WITH HIGHEST TOTALS EXPECTED CLOSER TO INTERSTATE 80.
ADDITIONALLY, SOUTH-SOUTHEAST WINDS ARE EXPECTED TO BECOME GUSTY
ON WEDNESDAY. GENERALLY GUSTS 25 TO 35 MPH ARE ANTICIPATED
THROUGHOUT THE VALLEY/FOOTHILLS, WITH GUSTS UP TO 50 MPH POSSIBLE
ALONG THE SIERRA.
SNOW LEVELS ARE EXPECTED TO VARY THROUGH THIS FIRST WAVE OF
PRECIPITATION, WITH COLD TEMPERATURES INITIALLY ON TUESDAY GRADUALLY
NEARING SEASONAL NORMALS MOVING THROUGH THE REMAINDER OF THE WEEK.
AS A RESULT, SNOW LEVELS 3000 TO 4000 FEET ARE ANTICIPATED TUESDAY
INTO WEDNESDAY MORNING, RISING TO 4500 TO 5500 FEET BY WEDNESDAY
AFTERNOON, FURTHER SETTLING AROUND 6000 TO 7000 FEET BY THURSDAY.
WITH THE HEAVIEST PRECIPITATION EXPECTED OVERNIGHT TUESDAY INTO
WEDNESDAY WHEN SNOW LEVELS REMAIN LOWEST, IMPACTFUL SNOWFALL OF 4 TO
8 INCHES WILL BE POSSIBLE DOWN TO 3500 FEET THROUGH WEDNESDAY NIGHT
FOR THE COASTAL RANGE, SHASTA COUNTY MOUNTAINS, AND NORTHERN
SIERRA/SOUTHERN CASCADES. ADDITIONALLY, SNOWFALL ACCUMULATIONS OF 8
TO 18 INCHES ARE ANTICIPATED FOR THESE LOCATIONS ABOVE 4500 FEET,
WITH UP TO 2 FEET POSSIBLE OVER PEAKS. ADDITIONAL SNOWFALL
ACCUMULATIONS WILL BE POSSIBLE ABOVE 5500 FEET ALONG THE REMAINDER
OF THE SIERRA, INCLUDING INTERSTATE 80 AND HIGHWAY 50, WITH TOTALS 3
TO 6 INCHES POSSIBLE.
EXTENDED DISCUSSION (FRIDAY THROUGH MONDAY)
MOVING TOWARD THE END OF THE WEEK AND INTO NEXT WEEKEND,
PRECIPITATION CHANCES ARE EXPECTED TO PERSIST ACROSS INTERIOR
NORCAL. THIS WILL BE THE PRODUCT OF THE AFOREMENTIONED OFFSHORE
TROUGH BEGINNING TO SLIDE INLAND OVER THE WEEKEND. DESPITE THE
ONSHORE SHIFT, ENSEMBLE GUIDANCE INDICATES THAT THE TROUGH WILL
ONLY GRADUALLY PROGRESS EASTWARD WITH TIME, PROLONGING THE WINDOW
FOR ADDITIONAL PRECIPITATION IMPACTS THROUGH THE WEEKEND AND
POTENTIALLY INTO EARLY NEXT AS WELL. AS THIS SYSTEM BECOMES MORE
CENTERED OVER NORCAL, SNOW LEVELS LOOK TO FALL TO AROUND 4000 TO
5000 FEET AGAIN THROUGHOUT THE WEEKEND. WHILE EXACT DETAILS
REGARDING PRECIPITATION TOTALS FROM FRIDAY INTO EARLY NEXT WEEK
REMAIN SOMEWHAT UNCERTAIN, CURRENT PROBABILITIES OF PRECIPITATION
EXCEEDING 2 INCHES LINGER AROUND 40% TO 70% FOR THE DELTA,
CENTRAL/SOUTHERN SACRAMENTO VALLEY, AND NORTHERN SAN JOAQUIN
VALLEY, JUMPING TO 70% TO 90% PROBABILITIES ACROSS THE NORTHERN
SACRAMENTO VALLEY AND SURROUNDING TERRAIN, AS WELL AS ALONG THE
SIERRA. GIVEN LOWERING SNOW LEVELS THROUGH THE WEEKEND, ADDITIONAL
MOUNTAIN TRAVEL IMPACTS WILL BE POSSIBLE ALONG THE SIERRA, WITH
CURRENT PROBABILITIES OF EXCEEDING 1 FOOT OF SNOW AROUND 60% TO
80% ALONG THE SIERRA ABOVE 5000' THROUGH MONDAY.
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
PRIMARILY VFR CONDITIONS ACROSS INTERIOR NORTHERN CALIFORNIA
THROUGH AT LEAST 18Z. AROUND 20Z TUESDAY, MVFR CONDITIONS POSSIBLE
DUE TO SHOWERS IN THE VALLEY. DELTA AND NORTHERN SAN JOAQUIN
VALLEY LOCATIONS COULD HAVE BREEZY WINDS WITH SUSTAINED SPEEDS UP
TO 12KTS AND GUSTS UP TO 15KTS THROUGH 00Z TUESDAY. OTHERWISE,
SURFACE WINDS GENERALLY AT OR BELOW 12 KTS.
STO WATCHES/WARNINGS/ADVISORIES
FREEZE WARNING FROM 10 PM THIS EVENING TO 10 AM PST TUESDAY FOR
CARQUINEZ STRAIT AND DELTA-CENTRAL SACRAMENTO VALLEY-MOTHERLODE-
MOUNTAINS SOUTHWESTERN SHASTA COUNTY TO WESTERN COLUSA COUNTY-
NORTHEAST FOOTHILLS/SACRAMENTO VALLEY-NORTHERN SACRAMENTO VALLEY-
NORTHERN SAN JOAQUIN VALLEY-SHASTA LAKE AREA / NORTHERN SHASTA
COUNTY-SOUTHERN SACRAMENTO VALLEY.
WINTER STORM WARNING FROM 4 PM TUESDAY 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 TUESDAY 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.
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