000
FXUS66 KSTO 152219
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
219 PM PST SUN DEC 15 2024
SYNOPSIS
A QUICK MOVING SYSTEM BRINGS ADDITIONAL PRECIPITATION IMPACTS TO
INTERIOR NORCAL LATE TONIGHT 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
AS OF EARLY THIS AFTERNOON, PARTLY TO MOSTLY CLOUDY SKIES ARE
EVIDENT ACROSS INTERIOR NORCAL VIA LATEST GOES-WEST SATELLITE
IMAGERY. EARLY MORNING FOG HAS SINCE LIFTED INTO A RATHER ROBUST
STRATUS DECK BLANKETING PORTIONS OF THE DELTA, SOUTHERN
SACRAMENTO, AND NORTHERN SAN JOAQUIN VALLEY MOST OF TODAY. THIS
STRATUS DECK IS BEGINNING TO GRADUALLY ERODE AS DAYTIME HEATING
AND MIXING OCCURS, BUT STILL PERSISTS AS OF 2 PM PST. OTHERWISE,
DRY CONDITIONS HAVE PREVAILED MUCH OF THE DAY ACROSS THE REGION AS
A BRIEF LULL BETWEEN SYSTEMS HAS ALLOWED HIGH TEMPERATURES TO
WARM TO NEAR NORMAL AMIDST A LIGHT NORTH TO EAST BREEZE. PRIOR TO
THE NEXT QUICK MOVING SYSTEM MOVING THROUGH, THERE WILL BE SOME
POTENTIAL FOR FOG DEVELOPMENT FOR MOST VALLEY AND DELTA LOCATIONS
FROM ROUGHLY CHICO SOUTHWARD. PROBABILITIES OF VISIBILITY LESS
THAN 1 MILE ON MONDAY MORNING ARE CURRENTLY AROUND 20% TO 40% FOR
THESE LOCATIONS. WHILE LINGERING LOW STRATUS MAY LOCALLY ENHANCE
FOG POTENTIAL, EXPECTED SOUTHERLY WINDS BECOMING BREEZY THROUGH
THE MORNING MAY EQUALLY HINDER FOG DEVELOPMENT AS WELL.
THIS PERIOD OF RELATIVE CALM IS EXPECTED TO REMAIN FAIRLY SHORT
LIVED FOR THE TIME BEING AS THE NEXT SHORTWAVE TROUGH CAN ALREADY
BE SEEN APPROACHING THE WEST COAST. WHILE THIS TROUGH IS GENERALLY
EXPECTED TO TRACK ACROSS THE PACIFIC NORTHWEST, THE THERE WILL BE
ENOUGH OF A SOUTHWARD COMPONENT THAT WILL BRING APPRECIABLE
PRECIPITATION IMPACTS TO INTERIOR NORCAL LATE TONIGHT INTO MONDAY.
AS A RESULT, A WINTER WEATHER ADVISORY IS IN EFFECT FOR THE
SHASTA COUNTY MOUNTAINS AND COAST RANGE AT ELEVATIONS ABOVE 3000
FEET FROM 10 PM TONIGHT THROUGH 4 AM TUESDAY, AND A SIMILAR WINTER
WEATHER ADVISORY IN EFFECT FROM 4 AM MONDAY THROUGH 4 AM TUESDAY
ALONG THE SIERRA AT ELEVATIONS ABOVE 5000 FEET. RESULTANT
PROBABILITIES OF EXCEEDING 6 INCHES OF SNOWFALL SIT AROUND 60% TO
90% ACROSS THE SHASTA COUNTY MOUNTAINS AND COAST RANGE, WITH 40%
TO 70% PROBABILITIES ALONG THE SIERRA.
AT LOWER ELEVATIONS ACROSS INTERIOR NORCAL, RAIN SHOWERS ARE
ANTICIPATED, WITH 40% TO 70% PROBABILITIES OF EXCEEDING 0.25
INCHES OF LIQUID PRECIPITATION FOR VALLEY AND FOOTHILLS LOCATIONS
FROM INTERSTATE 80 NORTHWARD, FALLING TO 15% TO 30% PROBABILITIES
GENERALLY SOUTH OF INTERSTATE 80. AS AFOREMENTIONED SOUTHERLY
WINDS LOOK TO INCREASE MONDAY MORNING, THEY ARE NOT EXPECTED TO
BECOME PARTICULARLY GUSTY OUTSIDE OF THE SIERRA CREST. GUSTS 15 TO
25 MPH WILL BE POSSIBLE ACROSS LOWER ELEVATIONS ON MONDAY, WITH
GUSTS 30 TO 40 MPH ANTICIPATED ALONG THE HIGH ELEVATION OF THE
SIERRA.
AS QUICKLY AS THIS SYSTEM ARRIVES, AMPLIFIED RIDGING LOOKS TO
RAPIDLY BUILD IN BEHIND FROM TUESDAY INTO THE MIDDLE OF THE WEEK.
THE INITIAL RIDGE/TROUGH INTERACTION MAY RESULT IN SOME BREEZY
NORTHERLY WINDS ON TUESDAY, BUT OTHERWISE DIURNAL/TERRAIN DRIVEN
WINDS CAN BE EXPECTED INTO THE MIDDLE OF THE WEEK. THE PRIMARY
SHIFT IN THE PATTERN WILL BE A TRANSITION TO DRIER WEATHER AND
SLIGHTLY ABOVE NORMAL HIGH TEMPERATURES. FROM TUESDAY THROUGH
THURSDAY, UPPER 50S TO LOW 60S ANTICIPATED ACROSS THE DELTA,
VALLEY, AND FOOTHILLS, WHILE EVEN UPPER 40S TO MID 50S EMERGE AT
HIGHER ELEVATIONS. WHILE RIDGING ALOFT WILL KEEP INTERIOR NORCAL
DRY AND WARM, IT WILL ALSO INTRODUCE AT LEAST SOME POTENTIAL FOR
FOGGY MORNINGS WITHIN THE VALLEY AS WELL.
EXTENDED DISCUSSION (THURSDAY THROUGH SUNDAY)
ENSEMBLE GUIDANCE FROM LATE WEEK INTO NEXT WEEKEND CONTINUES TO
INDICATE A GENERAL SHIFT BACK TOWARD A MORE ACTIVE WEATHER
PATTERN, BUT STARK DIFFERENCES REMAIN REGARDING TIMING AND
LOCATION OF ANY ATTENDANT SYSTEMS MOVING THROUGH THE FLOW PATTERN.
AS A RESULT, THERE IS SOME POTENTIAL THAT THE RIDGE HOLDS LONG
ENOUGH FOR WARM WEATHER TO PERSIST INTO FRIDAY BEFORE
PRECIPITATION CHANCES RETURN. THERE IS AN OVERALL CONSENSUS THAT
INCREASING PRECIPITATION CHANCES ARE LOOKING MORE LIKELY BY THE
WEEKEND THOUGH. WITH THESE INCREASING PRECIPITATION CHANCES,
TEMPERATURES ALSO LOOK TO COOL BACK TO NEAR NORMAL VALUES DURING
THIS TIME AS WELL. AS THE EXTENDED PORTION OF THE FORECAST
CURRENTLY HOLDS THE HIGHEST UNCERTAINTY, BE SURE TO FOLLOW LATEST
FORECAST TRENDS MOVING INTO NEXT WEEKEND.
AVIATION
LINGERING MVFR/IFR POSSIBLE IN VALLEY/DELTA LOW STRATUS THROUGH
THE EVENING, WITH RENEWED BR/FG POTENTIAL AFTER 06Z. ADDITIONAL
MVFR/IFR REDUCTIONS POSSIBLE AT RDD AND RBL AFTER 06Z AS THE NEXT
WEATHER SYSTEM MOVES IN, WITH SOME LIFR THEN POSSIBLE IN SNOW
SHOWERS ALONG THE SIERRA AFTER 12Z. SOUTHERLY WINDS GENERALLY LESS
THAN 12 KTS EXPECTED MOST LOCATIONS BY MONDAY MORNING, ALTHOUGH
SIERRA CREST WINDS GUSTING TO 35 KTS POSSIBLE AFTER 12Z.
STO WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 AM PST
TUESDAY FOR MOUNTAINS SOUTHWESTERN SHASTA COUNTY TO WESTERN
COLUSA COUNTY-SHASTA LAKE AREA / NORTHERN SHASTA COUNTY.
WINTER WEATHER ADVISORY FROM 4 AM MONDAY TO 4 AM PST TUESDAY FOR
WEST SLOPE NORTHERN SIERRA NEVADA-WESTERN PLUMAS COUNTY/LASSEN
PARK.
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