957
FXUS66 KSTO 082111
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
111 PM PST SAT FEB 8 2025
SYNOPSIS
COLD WEATHER AND PERIODICALLY BREEZY WINDS PERSIST THROUGH THE
WEEKEND AND INTO THE WEEK AHEAD. A ROBUST WEATHER SYSTEM THEN
BRINGS RENEWED CHANCES FOR MODERATE TO HEAVY RAIN AND MOUNTAIN
SNOW AND GUSTY SOUTHERLY WINDS MID TO LATE WEEK.
DISCUSSION
AS OF EARLY THIS AFTERNOON, MOSTLY SUNNY SKIES ACROSS INTERIOR
NORCAL ARE BEING ACCOMPANIED BY A LIGHT, BUT BRISK NORTHERLY WIND.
WHILE BROAD TROUGHING TO THE EAST AND ATTENDANT NORTHWESTERLY
FLOW ALOFT ARE EXPECTED TO CONTINUE INFLUENCING THE REGION INTO
EARLY NEXT WEEK, COLD TEMPERATURES AND BREEZY NORTHERLY WINDS WILL
PRIMARILY BE THE RESULTANT IMPACTS. HIGH TEMPERATURES THROUGH
TUESDAY ARE EXPECTED TO FLUCTUATE VERY LITTLE, GENERALLY SITTING
IN THE MID TO UPPER 50S FOR THE DELTA, VALLEY, AND FOOTHILLS, WITH
40S TO LOW 50S AT HIGHER ELEVATIONS. ADDITIONALLY, LOW
TEMPERATURES WILL SHOW A SIMILAR STABILITY, WITH LOW TO MID 30S
FOR MUCH OF THE DELTA, VALLEY, AND FOOTHILLS, AND TEENS TO MID 20
AT HIGHER ELEVATIONS THROUGH TUESDAY MORNING. COLDEST TEMPERATURES
ARE EXPECTED INTO MONDAY MORNING, WHERE DELTA, VALLEY, AND
FOOTHILLS PROBABILITIES OF LESS THAN 30F SIT AROUND 30 TO 50
PERCENT AND PROBABILITIES OF LOW TEMPERATURES LESS THAN 15F ALONG
THE SIERRA/SOUTHERN CASCADES LOCATIONS ABOVE 6000 FEET SIT AROUND
50 TO 80 PERCENT.
GIVEN THE PERSISTENT NORTHWESTERLY FLOW ALOFT EXPECTED THROUGHOUT
THE SHORT TERM, BREEZY NORTHERLY WINDS LOOK TO PREVAIL AS WELL.
STRONGEST GUSTS ARE ANTICIPATED LATE TONIGHT INTO SUNDAY AS A WEAK
MID LEVEL JET PULSES UP ACROSS THE NORTHERN AND CENTRAL
SACRAMENTO VALLEY. AS A RESULT, NORTHERLY WIND GUSTS OF 25 TO 35
MPH ARE EXPECTED PRIMARILY ALONG AND WEST OF THE INTERSTATE 5
CORRIDOR, WITH PROBABILITIES OF EXCEEDING 40 MPH GUSTS ONLY AROUND
15 TO 30 PERCENT AT THIS TIME.
EXTENDED DISCUSSION (WEDNESDAY THROUGH SATURDAY)
ENSEMBLE GUIDANCE REMAINS CONSISTENT WITH REGARDS TO THE EVOLVING
UPPER LEVEL PATTERN CHANGES EXPECTED ACROSS THE MID TO LATE WEEK
TIME FRAME. A LONGWAVE TROUGH EJECTING FROM THE GREAT BASIN TOWARD
THE PLAINS LOOKS TO BE RAPIDLY FOLLOWED BY A BUILDING SHORTWAVE
DEEPENING SOUTHWARD FROM THE GULF OF ALASKA BY LATE WEDNESDAY. THE
PRIMARY UNCERTAINTY WITH THE EVOLUTION OF THIS SYSTEM REMAINS
TIED TO THE TIMING AND MAGNITUDE OF WARM AIR AND MOISTURE
ADVECTION AND THE RESULTING INTERACTION WITH ANTECEDENT COLD, DRY
AIR ALREADY IN PLACE. DESPITE THE EXPECTED RAPID INTRODUCTION OF
THE SHORTWAVE, THERE ARE CURRENTLY SOME INDICATIONS WITHIN
ENSEMBLE GUIDANCE THAT THIS MAY LAG JUST ENOUGH FOR WARM AIR
ADVECTION TO OVERRUN MUCH OF THE COLD AIR PRIOR TO THE RETURN OF
APPRECIABLE MOISTURE. ALL THIS TO SAY, WHILE LOWER ELEVATION
SNOWFALL ACROSS THE NORTHERN SACRAMENTO VALLEY, PARTICULARLY INTO
THE REDDING AND SHASTA LAKE AREAS, IS STILL A POSSIBILITY,
PROBABILITIES OF UP TO 2 INCHES OF SNOWFALL IN THESE LOCATIONS HAS
FALLEN FROM 15 TO 30 PERCENT YESTERDAY, TO 5 TO 10 PERCENT TODAY.
A SIMILAR TREND IS EVIDENT ALONG THE SIERRA/SOUTHERN CASCADES
FOOTHILLS, WITH PROBABILITIES OF UP TO 2 INCHES FALLING TO 5 TO 15
PERCENT AT THIS TIME.
DESPITE THE UNCERTAINTIES REGARDING SNOW LEVELS AND LOWER
ELEVATION SNOWFALL, THERE IS INCREASING CONFIDENCE IN THE
EXPECTATION FOR PERIODS OF MODERATE TO HEAVY RAIN AND MOUNTAIN
SNOW ELSEWHERE. WHILE DEEPEST MOISTURE IS EXPECTED TO REMAIN
DISPLACED TOWARD SOCAL, PRECIPITABLE WATER ANOMALIES AROUND 150 TO
180 PERCENT OF NORMAL FOR THE TIME OF YEAR ACROSS INTERIOR NORCAL
ARE BEING INDICATED TO ACCOMPANY THIS SYSTEM. AS A RESULT,
PROBABILITIES OF EXCEEDING 2 INCHES OF RAINFALL SIT AROUND 20 TO
40 PERCENT ACROSS THE DELTA, VALLEY, AND FOOTHILLS, WITH 60 TO 90
PERCENT PROBABILITIES ALONG THE SIERRA. ACKNOWLEDGING THAT
FORECAST SNOW LEVELS WILL LIKELY CONTINUE FLUCTUATING OVER THE
NEXT SEVERAL DAYS IN THE LEAD UP TO THIS STORM, THE MAJORITY OF
ACCUMULATING SNOWFALL ALONG THE SIERRA/SOUTHERN CASCADES IS
ANTICIPATED ABOVE 4500 FEET AND ABOVE 3500 FEET ACROSS THE COAST
RANGE/SHASTA COUNTY MOUNTAINS. RESULTANT PROBABILITIES OF SNOWFALL
GREATER THAN 1 FOOT SIT AROUND 50 TO 70 PERCENT FOR THE COAST
RANGE/SHASTA COUNTY MOUNTAIN LOCATIONS, WITH 60 TO 80 PERCENT
PROBABILITIES OF SNOWFALL EXCEEDING 2 FEET FOR SIERRA/SOUTHERN
CASCADES LOCATIONS.
ADDITIONALLY, AS THE SHORTWAVE MOVES INLAND, A PERIOD OF GUSTY
SOUTHERLY WINDS AND ISOLATED THUNDERSTORM CHANCES IS EXPECTED TO
ACCOMPANY IT. ENSEMBLE GUIDANCE CONTINUES TO TREND TOWARD THIS
ONSHORE PUSH OCCURRING ON THURSDAY. RESULTANT PROBABILITIES OF
WIND GUSTS GREATER THAN 40 MPH SIT AROUND 40 TO 60 PERCENT FOR
DELTA, VALLEY, AND FOOTHILLS LOCATIONS FROM ROUGHLY CHICO
SOUTHWARD. WHILE AREAL THUNDERSTORM EXTENT WILL BE FURTHER
DICTATED BY THE TRACK OF THE APPROACHING SYSTEM, CURRENT 10 TO 15
PERCENT PROBABILITIES OF THUNDERSTORM DEVELOPMENT FAVOR VALLEY AND
FOOTHILLS LOCATIONS FROM INTERSTATE 80 SOUTHWARD AT THIS TIME.
AVIATION
GENERALLY, VFR CONDITIONS ACROSS INTERIOR NORCAL OVER THE NEXT 24
HOURS OUTSIDE OF A CHANCE (10-30%) FOR REDUCED VISIBILITIES FROM
BR ACROSS THE EASTERN PORTIONS OF THE NORTHERN SAN JOAQUIN VALLEY
12Z-18Z SUN. LIGHT NORTHERLY WINDS IN THE VALLEY TODAY, EXCEPT FOR
LOCAL GUSTS AROUND 15-20 KTS THROUGH 03Z SUNDAY. IN THE
SACRAMENTO VALLEY, AREAS OF NORTHERLY SURFACE WINDS 15-20 KTS WITH
GUSTS TO 25-30 KTS AFTER 06Z SUNDAY. IN NORTHEAST FOOTHILLS AND
MOUNTAINS, AREAS OF NORTHEAST TO EAST WINDS 15-20 KTS WITH LOCAL
GUSTS TO 25-35 KTS AFTER 06Z SUNDAY.
STO WATCHES/WARNINGS/ADVISORIES
NONE.
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