909
FXUS66 KSTO 192056
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1256 PM 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
DENSE FOG HAS LIFTED BY THIS POINT IN THE AFTERNOON, WITH ONLY
PATCHY FOG AND LOW STRATUS REMAINING IN SOME LOCATIONS. FOG
POTENTIAL CONTINUES TOMORROW, WITH A 50-70% CHANCE OF DENSE FOG
DEVELOPMENT (1/4 MILE VISIBILITY OR LESS) THROUGHOUT THE VALLEY
OVERNIGHT. IF YOU ENCOUNTER FOG WHILE DRIVING, BE SURE TO SLOW
DOWN AND ALLOW FOR EXTRA TIME TO REACH YOUR DESTINATION SAFELY.
OTHERWISE, DRY WEATHER CONTINUES THROUGH FRIDAY EVENING.
ON SATURDAY, THE FIRST OF SEVERAL WAVES OF PRECIPITATION BEGINS,
AS AN AREA OF LOW PRESSURE PUSHES A TROUGH THROUGH THE AREA. THIS
FIRST WAVE WILL BE RELATIVELY WARM, WITH SNOW LEVELS GENERALLY
ABOVE 6000 FT. THE NBM STILL HAS A 10 TO 20% PROBABILITY OF 2
INCHES OF SNOW OR MORE ABOVE 6000 FT, THOUGH THIS IS A DECREASE
FROM 24 HOURS AGO, AND THE MAJORITY OF SNOW WILL LIKELY BE A
DUSTING EXCEPT AT HIGHEST PEAKS. THE MAJORITY OF PRECIPITATION
THAT OCCURS ON SATURDAY WILL REMAIN AS RAIN, WITH THE NBM SHOWING
A 50 TO 75% CHANCE OF 1 INCH OR MORE OF RAINFALL IN THE NORTHERN
SACRAMENTO VALLEY, FOOTHILLS, AND MOUNTAINS. ELSEWHERE IN THE
VALLEY, THERE IS A 25 TO 50% CHANCE OF 0.5 INCHES OR MORE ON
SATURDAY.
OVERNIGHT ON SATURDAY, THERE WILL BE A BRIEF BREAK IN
PRECIPITATION BEFORE THE SECOND WAVE OF RAIN BEGINS. SNOW LEVELS
ON SUNDAY RISE TO ABOVE 8000 FT FOR THE MOST PART, SO NO SNOW IS
EXPECTED WITH THIS WAVE, EXCEPT POSSIBLY A DUSTING AT HIGHEST
PEAKS. THE NBM HAS A 30 TO 60% PROBABILITY OF 0.5 INCHES OR MORE
OF RAIN ON SUNDAY ACROSS MOST OF THE VALLEY, WITH A 60 TO 90%
CHANCE OCCURRING IN THE NORTHERN SACRAMENTO VALLEY, FOOTHILLS,
AND MOUNTAINS. 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 HWY 50. 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 LATE ON MONDAY. 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. 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 FOR THE NEXT 24 HOURS AND BR/FG MAY LIFT INTO A LOW
STRATUS DECK DURING THE DAY TIME, MAINLY ACROSS PORTIONS OF THE
SACRAMENTO AND NORTHERN SAN JOAQUIN VALLEYS. SURFACE WINDS
GENERALLY BELOW 12 KNOTS. LOCAL GUSTS UP TO 20 KTS IN THE
FOOTHILLS/SIERRA AFTER 10Z FRIDAY.
STO WATCHES/WARNINGS/ADVISORIES
NONE.
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