408
FXUS66 KSTO 202114
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
114 PM PST FRI DEC 20 2024
SYNOPSIS
MORNING FOG POTENTIAL INTO EARLY SATURDAY MORNING WILL BE
REPLACED BY PERIODIC CHANCES FOR PRECIPITATION AND GUSTY SOUTHERLY
WINDS AS A SERIES OF WEATHER SYSTEMS IMPACTS INTERIOR NORCAL FROM
MID MORNING SATURDAY INTO NEXT WEEK.
DISCUSSION
EARLY MORNING FOG ACROSS INTERIOR NORCAL TODAY HAS SINCE LIFTED
INTO A DECK OF LOW STRATUS COVERING MUCH OF THE VALLEY AND DELTA.
WHILE SOME STRATUS EROSION FROM THE EDGES IS ANTICIPATED THROUGH
THE AFTERNOON, THERE IS A HIGH PROBABILITY THAT MUCH OF THE
CENTRAL/SOUTHERN SACRAMENTO VALLEY AND DELTA WILL REMAIN MOSTLY
CLOUDY THROUGH THE DAY. WITH WINDS EXPECTED TO REMAIN LIGHT AND
NORTHERLY FOR MUCH OF THE EVENING AND OVERNIGHT PERIOD, ADDITIONAL
FOG DEVELOPMENT IS ANTICIPATED FOR THE DELTA AND MOST VALLEY
LOCATIONS AGAIN INTO SATURDAY MORNING. RESULTANT HREF
PROBABILITIES OF VISIBILITY LESS THAN 0.5 MILES SIT AROUND 60% TO
80% FOR DELTA AND VALLEY LOCATIONS BETWEEN REDDING TO MODESTO.
SATURDAY MORNING FOG DEVELOPMENT IS EXPECTED TO RAPIDLY
DETERIORATE FROM NORTH TO SOUTH BY MID MORNING AS SOUTH WINDS AND
PRECIPITATION CHANCES BOTH INCREASE INTO THE MORNING HOURS. THIS
PRECIPITATION ONSET WILL BE THE RESULT OF A LEADING SHORTWAVE
TRAVELING NORTHEASTWARD ALONG THE NORTHERN CALIFORNIA COAST TOWARD
THE PACIFIC NORTHWEST. A PLUME OF ATMOSPHERIC RIVER MOISTURE
LOOKS TO BECOME WRAPPED UP WITH THIS WAVE, BUT THE FURTHER
NORTHWARD EXTENT OF THIS INITIAL WAVE IS EXPECTED TO LIMIT THE
OVERALL UPSIDE OF PRECIPITATION TOTALS. AS A RESULT, HIGHEST
PROBABILITIES OF LIQUID PRECIPITATION EXCEEDING 0.5 INCHES AROUND
70% TO 90%, SIT ALONG THE NORTHERN SIERRA/SOUTHERN CASCADES AND
WITHIN THE NORTHERN SACRAMENTO VALLEY AND SURROUNDING TERRAIN AND
GENERALLY NORTH OF INTERSTATE 80. WITH SNOW LEVELS AROUND 6000 TO
7500 FEET FOR THIS INITIAL WAVE, MOST SNOWFALL ACCUMULATIONS
GREATER THAN AN INCH WILL BE CONFINED TO ELEVATIONS ABOVE 7000
FEET, WITH UP TO 6 INCHES POSSIBLE OVER PEAKS.
SOME SUBTLE ENSEMBLE DISCREPANCIES BETWEEN EXPECTED SHORTWAVES
DOES LOWER CONFIDENCE REGARDING THE TIMING OF THE NEXT WAVE, BUT
GENERAL CONSENSUS INDICATES A BRIEF BREAK IN PRECIPITATION EARLY
SUNDAY MORNING, WITH AN ADDITIONAL PUSH OF PRECIPITATION LATE
SUNDAY AFTERNOON INTO THE EVENING FOLLOWED BY A SOMEWHAT MORE
PRONOUNCED LULL FOR MUCH OF THE DAY ON MONDAY. GIVEN AN EVEN
FURTHER NORTHWARD CENTER OF THE PROGRESSIVE SUNDAY WAVE,
PROBABILITIES OF LIQUID PRECIPITATION EXCEEDING 0.5 INCHES ONLY
SIT AROUND 40% TO 60% FOR THE NORTHERN SACRAMENTO VALLEY AND
SURROUNDING TERRAIN TOWARD THE NORTHERN SIERRA/SOUTHERN CASCADES.
OTHERWISE, GIVEN THE COMPARATIVELY EXTENDED LULL INTO MONDAY,
MORNING FOG DEVELOPMENT MAY BE POSSIBLE, ALTHOUGH CURRENT
PROBABILITIES OF VISIBILITY LESS THAN 1 MILE ARE ONLY AROUND 10%
TO 20% AT THIS TIME. DESPITE THE RELATIVE LULL ON MONDAY, THE NEXT
WAVE IN THE SERIES IS EXPECTED TO MOVE TOWARD INTERIOR NORCAL
LATE MONDAY EVENING INTO TUESDAY BRINGING ADDITIONAL PRECIPITATION
IMPACTS TO THE REGION TOWARD THE MIDDLE OF THE WEEK.
EXTENDED DISCUSSION (TUESDAY THROUGH FRIDAY)
THIS NEXT STORM SYSTEM THAT ARRIVES LATE MONDAY THROUGH TUESDAY
WILL BE COLDER AND GENERALLY WETTER COMPARED TO THE WEEKEND
SYSTEMS. SNOW LEVELS WILL BE BETWEEN 5000-6000 FEET. THE NATIONAL
BLEND OF MODELS PROJECTS A 50-90% CHANCE OF 1.00 INCH OR MORE OF
RAIN AND A 30 TO 50% CHANCE OF 4 INCHES OF SNOW OR MORE. DRY
WEATHER IS THEN EXPECTED TO PREVAIL ON CHRISTMAS DAY WITH
SEASONABLE TEMPERATURES AND LIGHT NORTH WINDS BEFORE THE NEXT
SYSTEM ARRIVES LATE THAT NIGHT.
ON THURSDAY, THE ACTIVE PATTERN RESUMES AS ANOTHER STORM SYSTEM
BRINGS MORE RAIN AND MOUNTAIN SNOW CHANCES THROUGH FRIDAY. THE NBM
SHOWS A 60 TO 80% CHANCE OF EXCEEDING 1.00 INCH OF RAIN NORTH OF
I-80 WITH THIS SYSTEM AND A 30-60% CHANCE FOR 6.00 INCHES OR MORE
OF SNOW AT AROUND 5500-6000 FEET AND HIGHER. HIGHEST PRECIPITATION
AMOUNTS WITH BOTH SYSTEMS WILL BE FOCUSED OVER THE NORTHERN
SACRAMENTO VALLEY, SOUTHERN CASCADES, LASSEN NF/NP, AND THE SIERRA
AND ADJACENT FOOTHILLS. ADDITIONALLY WITH THESE SYSTEMS,
SOUTHERLY WINDS ARE FORECAST TO GUST 20 TO 35 MPH WITH A 20 TO 40%
CHANCE OF GUSTS EXCEEDING 40 MPH. THERE IS STILL MUCH UNCERTAINTY
WITH THIS LATER WEEK SYSTEM, SO STAY TUNED TO THE FORECAST FOR
UPDATES AS WE MOVE THROUGH THE WEEKEND WHEN ENSEMBLES AND CLUSTER
ANALYSIS COME INTO BETTER AGREEMENT.
AVIATION
MVFR/IFR IN LOW STRATUS EXPECTED THROUGH 06Z THEN INTRODUCING
AREAS OF LIFR IN BR/FG THROUGH 18Z SATURDAY, MAINLY ACROSS
PORTIONS OF THE DELTA AND SACRAMENTO AND NORTHERN SAN JOAQUIN
VALLEYS. MVFR/IFR/LIFR IN BR/FG THEN GRADUALLY REPLACED BY
MVFR/IFR IN SHRA FROM NORTH TO SOUTH AFTER 12Z. SURFACE WINDS
GENERALLY BELOW 12 KTS ALTHOUGH LOCAL GUSTS UP TO 20 KTS IN THE
FOOTHILLS/SIERRA.
STO WATCHES/WARNINGS/ADVISORIES
NONE.
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