234
FXUS66 KSTO 162117
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
117 PM PST MON DEC 16 2024
SYNOPSIS
A QUICK WEATHER SYSTEM IS BRINGING RAIN SHOWERS AND MODERATE
MOUNTAIN SNOW ACROSS INTERIOR NORCAL THROUGH THE REST OF TODAY.
DRIER AND WARMER WEATHER THEN ACCOMPANY POTENTIALLY FOGGY MORNINGS
THROUGH MID TO LATE WEEK. A RETURN TOWARD A MORE UNSETTLED
WEATHER PATTERN IS THEN EXPECTED BY THE WEEKEND AND INTO EARLY
NEXT WEEK.
DISCUSSION
CURRENT RADAR IMAGERY AS THE EARLY AFTERNOON SHOWS A SWATH OF
PRECIPITATION GRADUALLY MOVING EASTWARD FROM INTERSTATE 80
SOUTHWARD, WITH ADDITIONAL RETURNS ACROSS PORTIONS OF SHASTA,
TEHAMA, AND PLUMAS COUNTIES AS WELL. THIS ACTIVITY IS THE RESULT
OF A PROGRESSIVE SHORTWAVE TRAVERSING THE PACIFIC NORTHWEST.
DESPITE THE QUICK MOVING PROGRESSION, LOW ELEVATION RAIN SHOWERS
AND MOUNTAIN SNOWFALL IS EXPECTED TO CONTINUE THROUGH THE
AFTERNOON, TAPERING OFF TO PRIMARILY MOUNTAIN SNOW SHOWERS INTO
THE EVENING AND OVERNIGHT HOURS. AS A RESULT, THE WINTER WEATHER
ADVISORY FOR THE COAST RANGE/SHASTA COUNTY MOUNTAINS ABOVE 3000
FEET AND THE SIERRA/SOUTHERN CASCADES ABOVE 5000 FEET CONTINUES
THROUGH 4 AM TUESDAY MORNING. ADDITIONAL LIQUID PRECIPITATION
TOTALS OF 0.15 INCHES TO 0.50 INCHES WILL REMAIN POSSIBLE INTO
TUESDAY MORNING, WITH ADDITIONAL SNOWFALL ACCUMULATIONS OF 2 TO 5
INCHES AT THE AFOREMENTIONED ELEVATION LEVELS.
AMPLIFIED RIDGING ALOFT IS THEN EXPECTED TO QUICKLY BUILD IN ON
THE HEELS OF THE DEPARTING SYSTEM FROM TUESDAY THROUGH THE
REMAINDER OF THE WEEK. THIS WILL USHER IN A PERIOD OF DRIER AND
SEASONABLY WARMER WEATHER. RESULTANT HIGH TEMPERATURES IN THE
UPPER 50S TO LOW 60S ARE ANTICIPATED ACROSS THE DELTA, VALLEY, AND
FOOTHILLS, WITH UPPER 40S TO MID 50S AT HIGHER ELEVATIONS. LIGHT
WINDS GENERALLY LOOK TO HOLD FROM A NORTH TO EAST DIRECTION, WITH
OCCASIONALLY BREEZY DOWNSLOPE WINDS DURING THE OVERNIGHT AND EARLY
MORNING HOURS. GIVEN THE EXPECTED SHIFT TO A MORE STAGNANT
WEATHER PATTERN FOLLOWING THE RECENT WETTER WEATHER, MORNING FOG
POTENTIAL ACROSS PORTIONS OF THE DELTA AND VALLEY IS EXPECTED TO
RETURN AS WELL. CURRENT HREF PROBABILITIES OF VISIBILITY LESS THAN
0.5 MILES SIT AROUND 40% TO 70% FOR TUESDAY MORNING AND WEDNESDAY
MORNING FROM ROUGHLY CHICO SOUTHWARD, WITH NBM PROBABILITIES OF
VISIBILITY BELOW 1 MILE PERSISTING AROUND 20% TO 40% FOR THURSDAY
MORNING ACROSS A SIMILAR AREA.
EXTENDED DISCUSSION (FRIDAY THROUGH MONDAY)
WHILE THERE IS STILL SOME DISAGREEMENT ON THE EXACT TIMING OF THE
WEEKEND TROUGH, ENSEMBLES AND CLUSTER ANALYSIS SEEM TO HAVE COME
INTO BETTER AGREEMENT ON THE STRENGTH AND POSITIONING OF THE
TROUGHING PATTERN. SOME SOLUTIONS HAVE A SLIGHTLY MORE DELAYED
ONSET OF THE TROUGH PROGRESSING THROUGH NORCAL, THOUGH GENERALLY
BY 6 HOURS OR LESS. CURRENTLY THE NBM IS STILL SHOWING THE BULK OF
PRECIPITATION OCCURRING IN THE NORTHERN SACRAMENTO VALLEY AND
FOOTHILLS, AND NORTHERN SIERRA AND SOUTHERN CASCADES.
PROBABILITIES OF 1 INCH OR MORE RANGE FROM 40 TO 75% IN THESE
AREAS. THE REMAINDER OF THE VALLEY IS CURRENTLY LOOKING AT A 35 TO
70% PROBABILITY OF 0.5 INCHES OR MORE OF PRECIPITATION. THIS
SYSTEM APPEARS TO BE FAIRLY WARM, WITH SNOW LEVELS GENERALLY
STAYING ABOVE 6500 TO 7000 FEET. MONDAY SHOULD SEE DRIER
CONDITIONS AGAIN, THOUGH THIS MAY BE SHORT LIVED AS A LARGER LOW
PRESSURE SYSTEM LOOKS TO POTENTIALLY MOVE ONSHORE LATER DURING
CHRISTMAS WEEK. THE FORECAST IS HIGHLY UNCERTAIN THIS FAR OUT
HOWEVER, SO CHECK BACK REGULARLY FOR UPDATES AS DETAILS BECOME
MORE CLEAR.
AVIATION
MVFR/IFR CONDITIONS IN LOW STRATUS, RAIN/MOUNTAIN SNOW SHOWERS,
AND BR CONTINUE ACROSS INTERIOR NORCAL THROUGH AROUND 05Z TUESDAY,
WITH GENERALLY MVFR CEILINGS PREVAILING AFTER. SIERRA GUSTS TO 40
KTS POSSIBLE THROUGH 11Z, WITH WINDS LESS THAN 12 KTS EXPECTED
ELSEWHERE. SOME MVFR/IFR AND AREAS OF LIFR THEN POSSIBLE IN BR/FG
AFTER 11Z.
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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