363
FXUS66 KSTO 201019
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
219 AM PST FRI DEC 20 2024
SYNOPSIS
DRY WEATHER WITH MORNING FOG EXPECTED TODAY FIRST STORM IN A
SERIES OF SYSTEMS WILL MOVE INTO AREA SATURDAY FOLLOWED BY MORE
SYSTEMS INTO MID WEEK NEXT WEEK INCLUDING CHRISTMAS.
DISCUSSION
AREAS OF DENSE FOG HAVE DEVELOPED AROUND THE SACRAMENTO VALLEY
ONCE AGAIN THIS MORNING. LOWEST VISIBILITIES ARE BEING OBSERVED IN
THE NORTHERN SACRAMENTO VALLEY, WITH REDDING AP AT 1/4 MILE AND
RED BLUFF AP AT 1/2 MILE. LOW VISIBILITIES DUE TO FOG ARE EXPECTED
TO CONTINUE THIS MORNING, AND A DENSE FOG ADVISORY IS IN EFFECT
FOR THE SACRAMENTO AND NORTHERN SAN JOAQUIN VALLEY UNTIL 11 AM
THIS MORNING. IF YOU ENCOUNTER AREAS OF DENSE FOG ON THE MORNING
COMMUTE, SLOW DOWN, LEAVE PLENTY OF SPACE BETWEEN YOU AND THE CAR
IN FRONT OF YOU, AND USE YOUR LOW-BEAM HEADLIGHTS.
OUTSIDE OF THE MORNING FOG, TODAY WILL BE THE LAST DRY AND QUIET
WEATHER DAY FOR THE AREA, AS A SERIES OF STORMS IS EXPECTED TO
MOVE INTO THE AREA BEGINNING TOMORROW MORNING. AN AREA OF LOW
PRESSURE IN THE PACNW WILL EJECT A RELATIVELY WARM TROUGH WITH
PRECIPITATION CHANCES ACROSS THE AREA. THE BETTER MOISTURE WITH
THIS SYSTEM STILL LOOKS TO REMAIN MOSTLY NORTH OF OUR AREA,
HOWEVER THE NORTHERN SACRAMENTO VALLEY, SOUTHERN CASCADES, AND THE
SIERRA AND ADJACENT FOOTHILLS WILL SEE THE HEAVIEST OF
PRECIPITATION. LATEST RAIN TOTALS FROM THIS FIRST WAVE HAVE
REMAINED UNCHANGED FROM YESTERDAY'S FORECAST. AFOREMENTIONED
LOCATIONS STAND TO RECEIVE AROUND 0.75 TO 1.25 INCHES OF RAINFALL
THROUGH EARLY SUNDAY MORNING. SNOW LEVELS CONTINUE TO REMAIN ABOVE
6000 FEET FOR THE SIERRA, AND AROUND 5500 FEET FOR THE MOUNTAINS
OF NW SHASTA COUNTY. TOTAL SNOW ACCUMULATIONS LOOK TO REMAIN
AROUND A DUSTING TO 2 INCHES, WITH LOCALLY HIGHER AMOUNTS ON PEAKS
AND SPECIFICALLY AT LASSEN NF/NP.
LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING, A BRIEF BREAK FROM
WIDESPREAD RAIN/SHOWERS AND HIGH ELEVATION SNOW IS EXPECTED.
ANOTHER WAVE OF PRECIPITATION THEN ENTERS THE AREA SUNDAY MORNING,
WITH SIMILAR IMPACTS AND SNOW LEVELS ABOVE 8000 FEET, AS WARM
SOUTHERLY AIR CONTINUES TO FLOW INTO THE AREA. NBM PROBABILITIES
REMAIN AT AROUND 15-30% FOR LOCATIONS IN THE CENTRAL/SOUTHERN
SACRAMENTO VALLEY, DELTA, AND NORTHERN SAN JOAQUIN VALLEYS, WHILE
A 65-90% CHANCE FOR 0.50 INCHES IN THE NORTHERN SACRAMENTO VALLEY,
MOUNTAINS AND FOOTHILLS THROUGH MONDAY MORNING. OVERALL, MOUNTAIN
TRAVEL THIS WEEKEND DOES NOT LOOK TO BE MAJORLY IMPACTED, WITH
PRIMARILY WET ROADS AS THE POTENTIAL TRAVEL CONCERN. ANOTHER
BRIEF REPRIEVE FROM WIDESPREAD PRECIPITATION IS EXPECTED MONDAY
AFTERNOON, THEN A THIRD, WETTER, AND COOLER SYSTEM IS EXPECTED TO
MOVE IN.
THE THIRD SYSTEM IS EXPECTED TO BRING PRECIPITATION CHANCES MONDAY
AFTERNOON THROUGH EARLY CHRISTMAS DAY. OF THE THREE SYSTEMS IN THE
SHORT TERM FORECAST WINDOW, THIS SYSTEM WILL HAVE BETTER MOISTURE
SUPPORT FOR THE ENTIRE REGION. WHILE THE HIGHER PRECIPITATION
TOTALS WILL STILL BE IN THE NORTHERN SACRAMENTO VALLEY, MOUNTAINS
OF SHASTA COUNTY, SOUTHERN CASCADES, LASSEN NF/NP, AND THE SIERRA
AND ADJACENT FOOTHILLS. NBM PROBABILITIES OF AT LEAST AN INCH OF
RAINFALL THROUGH EARLY CHRISTMAS MORNING ARE AROUND 70-100% FOR
THE ABOVE MENTIONED AREAS, WHILE THE REST OF THE VALLEY, MAINLY
FROM REDDING SOUTHWARD 40-70% CHANCE OF AN INCH. COOLER AIR IS
ANTICIPATED TO RUSH IN BEHIND THIS SYSTEM, SO SNOW LEVELS WILL
FALL AS THE MAIN WAVE MAKES LANDFALL AND PUSHES INLAND. SNOW
LEVELS BEGIN AT AROUND 8000 FEET MONDAY NIGHT/TUESDAY MORNING,
THEN FALL TO AROUND 5000-6000 FEET TUESDAY NIGHT. WHILE THE BULK
OF THE PRECIPITATION WILL HAVE MOVED OUT OF THE AREA AS THE
COLDEST AIR ARRIVES, ACCUMULATIONS OF SNOW COULD IMPACT CHRISTMAS
EVE TRAVEL DURING THE NIGHTTIME AT AROUND 6000 FEET AND HIGHER.
NBM PROBABILITIES OF AROUND 6 INCHES OF SNOW AT ELEVATIONS 6000
FEET AND HIGHER ARE AROUND 30-50%, SO WE ARE NOT ANTICIPATING
MAJOR IMPACTS TO TRAVEL AT THIS TIME, HOWEVER AN ADVISORY MAY BE
NEEDED TO COVER HIGHER SNOWFALL RATES AND ACCUMULATIONS. BREEZY
SOUTHERLY WINDS WILL ALSO ACCOMPANY THIS THIRD SYSTEM, WITH
STRONGEST WINDS IN THE VALLEY FROM YUBA CITY TO REDDING AND IN THE
MOUNTAINS AND FOOTHILLS OF THE SIERRA. IF YOU HAVE TRAVEL PLANS
THIS WEEKEND THROUGH CHRISTMAS, PLEASE CHECK ROAD CONDITIONS
BEFORE HEADING OUT, AND KEEP CHECKING THE FORECAST FOR CHANGES.
EXTENDED DISCUSSION (TUESDAY THROUGH FRIDAY)
AS MENTIONED IN THE SHORT-TERM FORECAST DISCUSSION, THE THIRD
SYSTEM WILL CONTINUE INTO EARLY CHRISTMAS DAY, THEN ANOTHER BREAK
IN PRECIPITATION IS LIKELY UNTIL LATER CHRISTMAS NIGHT. ENSEMBLES
DEPICT ANOTHER TROUGH EJECTING INTO THE AREA, SLIGHTLY FURTHER
SOUTH AND EASTWARD THAN PREVIOUS TROUGHS. WITH THE CURRENT
EC ENSEMBLE GUIDANCE TRACK, THIS SYSTEM WILL BE COOLER AND COULD
BRING WIDESPREAD PRECIPITATION TO THE REGION ALL DAY THURSDAY AND
INTO FRIDAY MORNING. EARLY FORECAST PRECIPITATION TOTALS MAY BE
RUNNING TOO HOT, AS PROBABILITIES OF SNOW IN THE MOUNTAINS ARE
AROUND 30-60% FOR 6 INCHES OF SNOW AT AROUND 5500-6000 FEET AND
HIGHER, BUT THE TOTALS FORECAST ARE AROUND 6-13 INCHES. HEAVIER
RAIN TOTALS LOOK TO ONCE AGAIN BE IN THE NORTHERN SACRAMENTO
VALLEY, SOUTHERN CASCADES, LASSEN NF/NP, AND THE SIERRA AND
ADJACENT FOOTHILLS, BUT AGAIN THE PROBABILITIES THE NBM ARE
SHOWING ARE SKEWED FROM THE FORECAST RAIN TOTALS. THERE IS MUCH
UNCERTAINTY WITH THIS SYSTEM, AS CLUSTERS HAVE TO RESOLVE A
DEFINITIVE SOLUTION TO TRACK AND STRENGTH. 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 WITH LIFR CONDITIONS IN BR/FG AND/OR LOW CEILINGS
EXPECTED THROUGH 20Z-22Z FRIDAY IN THE VALLEY. BR/FG MAY LIFT
INTO A LOW STRATUS DECK BEYOND 20Z-22Z FRIDAY. SURFACE WINDS
GENERALLY BELOW 12 KNOTS NEXT 24 HOURS, THEN INCREASING SOUTHERLY
WINDS AFTER 12Z SATURDAY. LOCAL GUSTS UP TO 20 KTS IN THE
FOOTHILLS/SIERRA THROUGH 18Z FRIDAY. MVFR / LOCAL IFR CONDITIONS
AFTER 06Z SATURDAY AS PACIFIC WEATHER SYSTEM MOVES THROUGH
INTERIOR NORCAL.
STO WATCHES/WARNINGS/ADVISORIES
DENSE FOG ADVISORY UNTIL 11 AM PST THIS MORNING FOR CARQUINEZ
STRAIT AND DELTA-CENTRAL SACRAMENTO VALLEY-NORTHERN SACRAMENTO
VALLEY-NORTHERN SAN JOAQUIN VALLEY-SOUTHERN SACRAMENTO VALLEY.
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