924
FXUS66 KSTO 160958
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
158 AM PST MON DEC 16 2024
SYNOPSIS
A QUICK MOVING SYSTEM BRINGS ADDITIONAL PRECIPITATION IMPACTS TO
INTERIOR NORCAL TODAY INTO EARLY TUESDAY, FOLLOWED BE DRIER
WEATHER THROUGH MID TO LATE WEEK. A SHIFT BACK TOWARD MORE ACTIVE
WEATHER MAY BE POSSIBLE BY NEXT WEEKEND, BUT DETAILS REMAIN QUITE
UNCERTAIN AT THIS TIME.
DISCUSSION
SOME AREAS OF PATCHY FOG HAVE DEVELOPED EARLY THIS MORNING, MAINLY
IN THE NORTHERN SAN JOAQUIN VALLEY NEAR STOCKTON AP. LIGHT
SOUTHERLY WINDS MAY HELP PUSH SOME FOG INTO THE SOUTHERN
SACRAMENTO CITY AREA, HOWEVER THERE REMAINS A LAYER OF STRATUS
VISIBLE ON GOES-18 SATELLITE IN PLACE OVER THE CENTRAL SACRAMENTO
VALLEY THAT MAY INHIBIT WIDESPREAD FOG DEVELOPMENT OVERNIGHT.
MISTY-LIKE CONDITIONS ARE PRESENT IN THE SACRAMENTO AREA,
LOWERING VISIBILITIES AT A FEW AIRPORTS. FURTHER NORTH INTO SHASTA
COUNTY ALONG THE COASTAL RANGE, AREAS OF MOUNTAIN SNOW AND RAIN
SHOWERS HAVE MOVED ONSHORE. SOME EARLY 6-HOUR PRECIPITATION TOTALS
AROUND SHASTA COUNTY HAVE ANYWHERE FROM A TRACE TO ROUGHLY 0.10"
OF AN INCH SO FAR. PRECIPITATION IS EXPECTED TO CONTINUE THROUGH
TODAY AND INTO EARLY TUESDAY.
A TROUGH ASSOCIATED WITH AN AREA OF LOW PRESSURE LOCATED IN THE
PACNW IS RESPONSIBLE FOR THE CURRENT PRECIPITATION IN THE AREA,
AND THE TROUGH WILL CONTINUE TO MOVE THROUGH THE REGION AS WE MOVE
THROUGH THE DAY. MOST OF THE PRECIPITATION IMPACTS WILL BE IN THE
NORTHERN SACRAMENTO VALLEY AND MOUNTAINS OF SHASTA COUNTY/LASSEN
NF, HOWEVER SOME PRECIPITATION IS ANTICIPATED TO MAKE IT FURTHER
SOUTH INTO THE REST OF THE VALLEY AND IN THE SIERRA AND SOUTHERN
CASCADES AND ADJACENT FOOTHILLS. OVERALL SNOWFALL TOTALS FOR THE
SHASTA COUNTY MOUNTAINS AND COASTAL RANGE LOOKS TO REMAIN ON
TRACK AT AROUND 5-12 INCHES WITH LOCALLY HIGHER AMOUNTS ON PEAKS
THROUGH TUESDAY AM. NBM PROBABILITIES REMAIN AT AROUND 60-90% FOR
6 INCHES OF SNOWFALL OR MORE THROUGH TUESDAY. FOR LOCATIONS IN THE
SIERRA AND SOUTHERN CASCADES, 3-8 INCHES IS EXPECTED, WITH THE
HIGHER TOTALS FORECAST NORTH OF I-80 AND SPECIFICALLY AT LASSEN
NF. NBM PROBABILITIES OF 4 INCHES OR MORE OF SNOWFALL ARE AROUND
20-60%, WITH HIGHER 80-90% PROBABILITIES AT LASSEN NF. AS A RESULT
OF THE PROJECTED SNOWFALL TOTALS, A WINTER WEATHER ADVISORY IS IN
EFFECT NOW FOR THE SHASTA MOUNTAINS AND COASTAL RANGE UNTIL 4 AM
TUESDAY FOR ELEVATIONS AT 3000 FEET AND ABOVE. THE SIERRA WINTER
WEATHER ADVISORY WILL GO INTO EFFECT AT 4 AM THIS MORNING THROUGH
4 AM TUESDAY FOR ELEVATIONS ABOVE 5000 FEET. IF YOU ARE TRAVELING
OR HAVE TO DRIVE THROUGH AREAS IN EITHER ADVISORY, BE SURE TO
CHECK ROAD CONDITIONS BEFORE HEADING OUT, AS TRAVEL DELAYS AND
CHAIN CONTROLS WILL BE POSSIBLE.
NOT MUCH CHANGE IN OVERALL FORECAST RAINFALL TOTALS FOR THE VALLEY
FROM THIS SYSTEM, WITH ANYWHERE FROM 0.10" IN MODESTO UP TO AROUND
0.50" FORECAST FOR REDDING. WITH THE CURRENT TRACK OF THIS SYSTEM,
MOST OF THE IMPACTS WILL BE FELT IN SHASTA COUNTY, AND THE
FOOTHILLS OF THE SIERRA IN TERMS OF RAINFALL. AS THE SYSTEM
VACATES THE AREA TUESDAY, WINDS WILL SHIFT FROM THE NORTH, HOWEVER
PGF WILL NOT BE AS STRONG AS LAST WEEKEND, THEREFORE WIND GUSTS
WILL GENERALLY BE BELOW 15 MPH EXCEPT IN THE HIGHER ELEVATIONS OF
THE SIERRA NEVADA. AS THE SYSTEM EXITS, UPPER LEVEL RIDGING IS
FORECAST TO DEVELOP AND HELP CLEAR AND DRY THINGS OUT THROUGH THE
END OF THE WEEK. HIGH TEMPERATURES WILL CLIMB TO SLIGHTLY ABOVE
NORMAL STARTING TUESDAY WITH HIGHS IN THE UPPER 50S TO LOW 60S FOR
THE VALLEY AND LOWER ELEVATIONS OF THE FOOTHILLS. HIGHER
ELEVATIONS WILL BE IN THE UPPER 40S TO MID 50S FROM TUESDAY
THROUGH THURSDAY.
EXTENDED DISCUSSION (FRIDAY THROUGH MONDAY)
ENSEMBLE GUIDANCE CONTINUES TO SUGGEST A POTENTIAL SHIFT TO MORE
ACTIVE WEATHER TOWARDS THE WEEKEND, HOWEVER MANY SOLUTIONS
REGARDING THE TRACK AND POTENTIAL PRECIPITATION IMPACTS EXIST.
CLUSTER ANALYSIS REVEALS THERE IS POTENTIAL FOR THE UPPER
LEVELTHEMSELVESRIDGING TO HOLD IN THE AREA FRIDAY, OR A MAKING
IT'S WAY INTO THE REGION. IF THE RIDGE HOLDS FRIDAY, WE MAY SEE A
DELAY OF THE ONSET OF PRECIPITATION UNTIL LATE FRIDAY NIGHT/EARLY
SATURDAY MORNING. CURRENT NBM QPF GUIDANCE IS SUGGESTING THAT ONCE
AGAIN, THE BULK OF THE IMPACTS WOULD BE ALONG THE NORTHERN
SACRAMENTO VALLEY AND THE FOOTHILLS OF THE SIERRA NEVADA/SOUTHERN
CASCADES. EARLY LOOK AT THE SNOW LEVELS ALSO SUGGESTS THIS SYSTEM
MAY BE WARMER THAN OUR PREVIOUS STORMS, WITH SNOW LEVELS AT AND
ABOVE 7000 FEET. WITH THE UNCERTAINTY REGARDING TRACK, LOCATION,
AND STRENGTH, CONTINUE TO CHECK BACK FOR UPDATES AS WE MOVE
THROUGH THE WORK WEEK AND THE DETAILS WILL START TO IRON OUT.
AVIATION
POTENTIAL FOR MVFR/IFR AND LOCAL LIFR FOR THE SOUTHERN SACRAMENTO
VALLEY/DELTA IN LOW STRATUS AND BR CONTINUES THROUGH AROUND 15Z,
WITH PATCHY FOG FOR THE NORTHERN SAN JOAQUIN VALLEY. LOW STRATUS
AND -RA WILL BRING MVFR/IFR REDUCTIONS FOR RDD AND RBL TODAY AS A
WEATHER SYSTEM MOVES IN. IFR AND LIFR ARE DEVELOPING IN SNOW
SHOWERS OVER THE NORTHERN COASTAL RANGE AND WILL SPREAD ALONG THE
SIERRA AFTER 12Z. SOUTHERLY WINDS GENERALLY LESS THAN 12 KTS
EXPECTED ACROSS THE VALLEY AND DELTA, WITH SIERRA CREST WINDS
GUSTING 25 TO 35 KTS AFTER 12Z.
STO WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 4 AM PST TUESDAY FOR MOUNTAINS
SOUTHWESTERN SHASTA COUNTY TO WESTERN COLUSA COUNTY-SHASTA LAKE
AREA / NORTHERN SHASTA COUNTY-WEST SLOPE NORTHERN SIERRA NEVADA-
WESTERN PLUMAS COUNTY/LASSEN PARK.
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