543
FXUS66 KSTO 191109
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
309 AM PST THU DEC 19 2024
SYNOPSIS
DRY WEATHER AND FOGGY MORNINGS ARE EXPECTED THROUGH FRIDAY. FIRST
STORM IN A SERIES OF SYSTEMS WILL MOVE INTO AREA SATURDAY
FOLLOWED BY MORE SYSTEMS INTO MID WEEK NEXT WEEK INCLUDING
CHRISTMAS.
DISCUSSION
ANOTHER MORNING OF DENSE FOG DEVELOPMENT BEING OBSERVED ACROSS
INTERIOR NORCAL, WITH VISIBILITIES LESS THAN 1/4 MILE CURRENTLY AT
KSMF. FOG HAS DEVELOPED FURTHER NORTH THIS MORNING AS WELL, WITH
RED BLUFF REPORTING 1/4 MILE VISIBILITY AT THE TIME OF THIS
WRITING. THE HREF CONTINUES TO SHOW DECENT CHANCES (50-70%) OF FOG
DEVELOPMENT ACROSS PORTIONS OF THE NORTHERN SACRAMENTO VALLEY, AS
FAR NORTH AS REDDING, AND INTO THE SOUTHERN/CENTRAL SACRAMENTO
VALLEY AND THE NORTHERN SAN JOAQUIN VALLEY THROUGH THE REMAINDER
OF THE MORNING AND INTO FRIDAY MORNING, ALTHOUGH FRIDAY WE MAY
SEE A BREAK IN WIDESPREAD FOG DEVELOPMENT AS OUR UPPER LEVEL AIR
PATTERN BEGINS TO SHIFT. REMINDER TO SLOW DOWN AND ALLOW FOR
EXTRA TIME TO REACH YOUR DESTINATIONS SAFELY DURING THE MORNING
COMMUTE.
WE WILL CONTINUE TO REMAIN DRY WITH SEASONABLE TEMPERATURES, AS
UPPER LEVEL RIDGING CONTINUES TO REMAIN IN PLACE OVER NORCAL. LATE
FRIDAY AND INTO SATURDAY, THE RIDGE WILL BEGIN TO TRANSLATE
TOWARDS THE EAST AND THE FIRST OF A SERIES OF ATMOSPHERIC RIVERS
BEGINS TO MOVE INTO THE REGION. THE FIRST WAVE ARRIVES SATURDAY
MORNING, AND THE INITIAL PUSH OF THE BETTER MOISTURE AND IVT
VALUES WILL BE FURTHER NORTH. THIS FIRST WAVE WILL MAINLY IMPACT
THE FAR NORTHERN PORTIONS OF THE CWA, INCLUDING REDDING, LASSEN
NP/NF, AND THE MOUNTAINS AND FOOTHILLS OF THE SOUTHERN CASCADES
AND NORTHERN SIERRA (INCLUDING I-80 AND AREAS NORTH). OVERALL
RAINFALL TOTALS LOOK TO REMAIN AROUND AN INCH FOR THE
AFOREMENTIONED LOCATIONS, WHILE LOCATIONS IN THE SACRAMENTO VALLEY
MAY SEE ANYWHERE FROM A TRACE TO A HALF-INCH, WITH LOWER TOTALS
FURTHER SOUTH AND IN THE DELTA. SINCE OUR AREA WILL BE RECEIVING
THE SOUTHERN EXTENT OF THE BETTER MOISTURE AND COLDER AIR, SNOW
TOTALS LOOK MEAGER AS SNOW LEVELS ARE CURRENTLY FORECAST TO BE
AROUND 6500-7500 FEET IN THE SIERRA, AND AROUND 5500-6500 FEET IN
THE MOUNTAINS OF NORTHWESTERN SHASTA COUNTY. CURRENTLY, THE
MOUNTAINS OF NORTHWESTERN SHASTA COUNTY AND LASSEN NF/NP LOOK TO
RECEIVE THE HIGHER TOTALS, WITH AROUND 2-8 INCHES ABOVE 6000 FEET.
LOCATIONS IN THE SIERRA MAY GET A DUSTING TO 2 INCHES INCLUDING
I-80/US-50, WITH THE BETTER CHANCES ABOVE PASS LEVELS. THE BULK OF
THIS WAVE'S PRECIPITATION WILL LIKELY FALL SATURDAY MORNING AND
INTO THE AFTERNOON, THEN WE HAVE A SHORT "BREAK" IN PRECIP, WITH
SCATTERED/ISOLATED SHOWERS, SATURDAY NIGHT INTO SUNDAY MORNING.
THE SECOND WAVE WILL ARRIVE LATE SUNDAY MORNING/EARLY AFTERNOON,
AND FOLLOW A SIMILAR PATTERN TO OUR FIRST WAVE. ONCE AGAIN, IT
APPEARS THE BULK OF THE BETTER MOISTURE AND COLD AIR ALOFT WILL BE
FURTHER NORTH OF OUR WARNING AREA. THE NORTHERN SACRAMENTO
VALLEY, LASSEN NF/NP, AND PORTIONS OF THE SOUTHERN CASCADES AND
NORTHERN SIERRA/FOOTHILLS WILL STAND THE BETTER CHANCES TO SEE
WIDESPREAD RAINFALL. CURRENT NBM PROBABILITIES OF SEEING AROUND AN
INCH OF RAINFALL SUNDAY ARE 40-80% FOR THE LOCATIONS MENTIONED
ABOVE, WHICH CORRESPONDS WELL TO THE ACTUAL QPF FORECASTS. WITH
WARM SOUTHERLY FLOW ALSO EMBEDDED WITH THIS SYSTEM, SNOW LEVELS
WILL BE WELL ABOVE PASS LEVELS, AROUND 7000-8500 FEET, SO LITTLE
TO NO SNOW ACCUMULATION IS ANTICIPATED WITH THIS SECOND WAVE.
OVERALL, WEEKEND TRAVEL ON SATURDAY AND SUNDAY WITH CURRENT SNOW
FORECASTS TO BE GENERALLY ABOVE PASS LEVELS, SHOULD NOT BE
MAJORLY IMPACTED. WET ROADS WILL LIKELY BE THE PRIMARY CONCERN
ALONG I-5, I-80, AND US50. AS ALWAYS, CHECK THE FORECAST
FREQUENTLY AND CHECK LIVE ROAD CONDITIONS AT QUICKMAP.DOT.CA.GOV
BEFORE TRAVELING.
EXTENDED DISCUSSION (MONDAY THROUGH THURSDAY)
MOST VALLEY LOCATIONS WILL SEE ANOTHER BRIEF "BREAK" FROM
WIDESPREAD RAIN LATE SUNDAY NIGHT, BUT A THIRD WAVE OF
PRECIPITATION WILL QUICKLY MOVE IN MONDAY AFTERNOON. THIS WAVE OF
MOISTURE HAS BETTER PWAT VALUES ASSOCIATED WITH IT, SO THIS SYSTEM
WILL BE WETTER AND BRING HIGHER RAIN TOTALS TO THE REGION. THE
NORTHERN SACRAMENTO VALLEY, SOUTHERN CASCADES, AND NORTHERN SIERRA
AND ADJACENT FOOTHILLS STAND THE BEST CHANCES OF RECEIVING 2+
INCHES OF RAINFALL. NBM PROBABILITIES ARE CURRENTLY 60-90% FOR
THOSE LOCATIONS, WHILE OTHER VALLEY LOCATIONS STAND AROUND A
40-60% CHANCE OF AT LEAST ONE INCH OF RAIN THROUGH EARLY
WEDNESDAY.
SNOW LEVELS WILL ONCE AGAIN START ABOVE PASS LEVELS WITH THIS
SYSTEM, HOWEVER THE CURRENT PROJECTIONS FROM ENSEMBLES SHOW THE
ASSOCIATED TROUGH DIGGING FURTHER SOUTH AND BRINGING IN COLDER AIR
BEHIND IT. TUESDAY NIGHT, SNOW LEVELS WILL FALL TO AROUND 5000
FEET, SO SNOW WILL BEGIN TO IMPACT ROADWAYS AND MAY EFFECT
HOLIDAY TRAVEL. NBM PROBABILITIES OF SNOWFALL TOTALS THROUGH
WEDNESDAY FOR 8 INCHES OF SNOW IN THE SIERRA NEVADA ARE AROUND
20-40% NEAR PASS LEVELS, HIGHER PROBS OF 60% FOR HIGHER
ELEVATIONS. PERIODS OF BREEZY SOUTHERLY WINDS WILL ALSO DEVELOP
MONDAY INTO TUESDAY, WITH GUSTS UP TO 35 MPH POSSIBLE IN PORTIONS
OF THE VALLEY. NBM SHOWS AROUND A 50-80% CHANCE OF 35 MPH GUSTS,
MAINLY NORTH OF SACRAMENTO AND IN THE FOOTHILLS/MOUNTAINS AND
CANYONS AND GAPS. THERE IS STILL MUCH UNCERTAINTY REGARDING THE
EXACT TRACK OF THE POTENTIAL CHRISTMAS WEATHER SYSTEM, SO STAY
TUNED FOR UPDATES AS DETAILS WILL BECOME MORE CLEAR AS WE MOVE
INTO THE WEEKEND.
AVIATION
MVFR/IFR WITH LIFR CONDITIONS IN BR/FG AND/OR LOW CEILINGS
EXPECTED THROUGH 20Z-22Z THURSDAY IN THE VALLEY, AND AGAIN AFTER
03Z-06Z FRIDAY. BR/FG MAY LIFT INTO A LOW STRATUS DECK BEYOND 22Z
THURSDAY, MAINLY ACROSS PORTIONS OF THE CENTRAL/SOUTHERN
SACRAMENTO AND NORTHERN SAN JOAQUIN VALLEYS. SURFACE WINDS
GENERALLY BELOW 12 KNOTS. LOCAL GUSTS UP TO 20 KTS IN THE
FOOTHILLS/SIERRA THROUGH 18Z THURSDAY AND AGAIN AFTER 06Z FRIDAY.
STO WATCHES/WARNINGS/ADVISORIES
DENSE FOG ADVISORY UNTIL NOON PST TODAY FOR CARQUINEZ STRAIT AND
DELTA-CENTRAL SACRAMENTO VALLEY-MOTHERLODE-NORTHERN SACRAMENTO
VALLEY-NORTHERN SAN JOAQUIN VALLEY-SOUTHERN SACRAMENTO VALLEY.
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