909
AGUS76 KRSA 250338
HMDRSA
HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
740 PM PST WED DEC 24 2025
..SCATTERED CONVECTION TONIGHT BEST ACROSS NORTHERN CA
..NEXT ROUND OF PRECIP FOR CHRISTMAS DAY INTO FRIDAY
..DRYING THROUGH THE WEEKEND
METEOROLOGICAL CONDITIONS (SHORT TERM: WED PM - SAT PM)
THE DEEP MOISTURE PLUME ADVECTING TOWARD SOUTHERN CA UNDER DEEP
SOUTHERLY FLOW AHEAD OF AN ADVANCING COLD FRONT HAS SHIFTED SOUTH
AND EAST OF THE REGION THIS EVENING. THE 25/00Z KNKX RAOB DID RECORD
A PW VALUE OF 1.47-INCHES AS THE MAIN MOISTURE PLUME WAS CROSSING
THE AREA...BUT NOW 3 HOURS LATER...TPW IMAGERY SHOWS AVAILABLE
MOISTURE DROPPING OFF AND PRECIP BECOMING MORE SCATTERED AND LIGHTER.
BEHIND THE COLD FRONT...A BROAD UPR TROF REMAINS ENTRENCHED
OFFSHORE WITH ITS AXIS STILL ALONG 135W. THE MAIN CONCERN THIS
EVENING IS SEVERAL AREAS OF CONVECTION THAT HAS DEVELOPED IN AN AREA
OF DIFFLUENT FLOW ALOFT AND A MID-LEVEL DISTURBANCE MOVING FROM
SOUTHWEST TO NORTHEAST. THE INITIAL AREA OF SHOWERS/T-STORMS
DEVELOPED NEAR THE SACRAMENTO AREA AND HAS TRACKED NORTHWARD TOWARD
THE CHICO/OROVILLE AREA. ANOTHER CLUSTER OF CELLS MOVED FROM NEAR
SAN FRANCISCO AND IS NOW CROSSING OVER THE RUSSIAN/NAPA RIVER
BASINS. AND A BIT FARTHER SOUTH OVER SANTA BARBARA AND VENTURA
COUNTIES...SEVERAL AREAS OF PRECIP ARE SHIFTING TO THE NNE. TRIED TO
CAPTURE THESE LOCATIONS WITH SOME HIGHER PRECIP TOTALS BLENDING IN
THE 25/00Z HRRR WITH SOME MANUAL ADJUSTMENTS UPWARD.
OVERNIGHT INTO CHRISTMAS DAY...A STRENGTHENING DISTURBANCE MOVING
THROUGH THE OFFSHORE UPR TROF WILL RIDE TO THE NORTHEAST WITH A
DEEPENING SFC LOW REACHING DOWN TO NEAR OR JUST BELOW 980-MB.
ALTHOUGH THIS SFC LOW IS A BIT FARTHER WEST THAN THE ONE FROM
EARLIER TODAY...IT HAS A LOWER MSLP. THIS WILL ONCE AGAIN RAMP UP
WINDS FROM THE SOUTH TO SOUTHEAST. FOR THIS FORECAST ISSUANCE...ONCE
AGAIN FELT IT WAS NEEDED TO INCREASE AMOUNTS ON THE EAST SLOPES OF
THE NORTHERN CA COASTAL MOUNTAINS AND THE WESTERN PORTION OF THE
SHASTA LAKE DRAINAGE OVERNIGHT. AS THIS DISTURBANCE ROTATES THROUGH
THE FLOW...IT WILL PUSH A NARROW MOISTURE PLUME WITH PW VALUES CLOSE
TO 1.00-INCH ACROSS COASTAL SOUTHERN CA FROM LATER TOMORROW MORNING
THROUGH FRIDAY MORNING. ALONG WITH LOW-LEVEL SOUTHWEST FLOW (NOT AS
IDEAL AS THE SOUTHERLY FLOW FROM TODAY AND LESS AVAILABLE
MOISTURE)...THE TRANSVERSE RANGES WILL SEE AN UPTICK IN PRECIP.
ALSO TOMORROW...THE SIERRA WILL SEE ANOTHER GOOD SHOT OF PRECIP
UNDER SOUTHWESTERLY FLOW AT 700-MB THAT WILL GENERATE UPSLOPE
CONDITIONS. WIDESPREAD TOTALS WILL RANGE FROM 1.00- TO 3.00-INCHES
WITH SOME LOCALIZED AMOUNTS FROM 4.00- TO 5.00-INCHES. FREEZING
LEVELS TOMORROW WILL GENERALLY START FROM 6000-FEET NORTH TO ABOUT
7500-FEET SOUTH AND THEN GRADUALLY LOWER INTO FRIDAY TO A RANGE OF
5000- TO 6000-FEET. THIS ALL HAPPENS AS THE UPR TROF FINALLY SWINGS
INLAND AND BECOMES POSITIVELY TILTED. AS FRIDAY PROGRESSES INTO
SATURDAY...LOOK FOR PRECIP TO TO TAPER OFF FROM NORTHWEST TO
SOUTHEAST.
QPF GRAPHICS ARE AVAILABLE AT WWW.CNRFC.NOAA.GOV/QPF.PHP
DRK
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