944
AGUS76 KRSA 232110
HMDRSA
HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
110 PM PST TUE DEC 23 2025
..SCATTERED SHOWERS ACROSS NRN CA REST OF TODAY
...NEXT ROUND OF WIDESPREAD MDT TO HVY PRECIP ARRIVES LATE
TONIGHT/WEDS THROUGH FRI, CHANCES OF T-STORMS PARTICULARLY ALONG THE
COAST...
METEOROLOGICAL CONDITIONS (SHORT TERM: TUE PM - FRI AM)
A SURFACE LOW CONTINUES TO APPROACH NRN CA FROM THE SOUTHWEST AS THE
MOISTURE PLUME OVER NRN CA HAS PULLED OFFSHORE. SHOWERS CONTINUE TO
FUNNEL INTO NW CA MAINLY WEST OF I-5 THANKS TO ENOUGH LINGERING
MOISTURE AND A FRONT/UPPER TROUGH. BIT OF A SURPRISE OVER THE SAN
DIEGO AREA LATE THIS MORNING AS MOISTURE GOT PULLED IN SOONER THAN
EXPECTED SENDING ABOUT 0.10" OF PRECIP ONSHORE. ADDITIONAL PERIODS
OF SHOWER ACTIVITY WILL BE POSSIBLE GOING FORWARD. FOR NW CA, OVER
THE PAST 6 HOURS OBSERVATIONS REPORT ANOTHER 0.25-0.75" WITH OVER
AN INCH AT SHASTA. MODELS HAVE ONCE AGAIN UNDER-ESTIMATED PRECIP IN
THAT AREA AND WILL LIKELY CONTINUE TO DO SO. ALREADY 0.10-0.30" HAS
FALLEN IN A LINE FROM HWY-101 IN MENDOCINO COUNTY NORTHEASTWARD TO
SHASTA IN THE PAST TWO HOURS, WHICH IS OVER THE ABOUT 0.10-0.25" THE
NBM HAS FOR THE ENTIRE 18Z-00Z TIME FRAME. ADJUSTED THE QPF FOR THAT
WINDOW IN THE AFTERNOON UPDATE.
OTHERWISE, THE FORECAST REMAINS ON TRACK FOR THAT SURFACE LOW AND
BROADER UPPER LEVEL SYSTEM TO BRING BACK ADDITIONAL MORE WIDESPREAD
MODERATE PRECIP LATER TODAY INTO THE EVENING. THE TROUGH AS IT GETS
CLOSER TO THE COAST WILL DRAG ADDITIONAL TROPICAL MOISTURE INTO CA
TONIGHT WITH A PARTICULAR FOCUS OVER SOUTHERN CA IN THE 06Z-12Z TIME
FRAME. THE DETAILS OF ALL THAT HAVE NOT CHANGED SINCE THIS MORNING
WITH RAIN RATES MORE WIDESPREAD OF 0.50+"/HR AND OVER 1"/HR OVER THE
TRANSVERSE IN THE 09Z-12Z TIME FRAME AS WELL AS EMBEDDED LOCALLY
ELSEWHERE ACROSS AREA MOUNTAINS. THUNDERSTORMS ARE STILL A CONCERN
WITH LOCALLY HIGHER RAINFALL TOTALS POSSIBLE THAN IN THE OFFICIAL
FORECAST. THE TIME FRAME FOR THE HEAVIEST PRECIP IS 06Z WEDS TO 00Z
THURS. AFTER THAT THE MOISTURE WILL EXIT TO THE SOUTH WHILE THE NEXT
BROADER SURFACE/UPPER LOW ARRIVE AND ROTATE ADDITIONAL WIDESPREAD
PRECIPITATION INTO CA THROUGH THE END OF THE SHORT TERM.
THE AFTERNOON UPDATE WAS GENERALLY A BLEND OF THE PREVIOUS FORECAST,
THE LATEST NBM, AND WPC GUIDANCE. INCREASED VALUES AGAIN FOR THE
OVERNIGHT TONIGHT TO WEDNESDAY MORNING TIME FRAME OVER THE
TRANSVERSE RANGE BY BLENDING IN THE 18Z HRRR. ALL EXCEEDANCE
PROBABILITIES CONTINUE TO SUGGEST BETWEEN 4-6" IN EACH 6 HOUR WINDOW
DURING THE PERIOD OF CONCERN. MODEL TRENDS CONTINUE TO DRY ACROSS
THE GREATER BAY AREA WHICH BROUGHT THE FORECAST DOWN ANOTHER 0.25-
0.75" BETWEEN NOW AND 12Z FRIDAY. HIGHER RESOLUTION MODELS TEND TO
HAVE LESS OF A BROAD BRUSH PAINTING OF PRECIP AND DIAL IN A LITTLE
MORE NARROWING THE GEOGRAPHY OF THOSE AMOUNTS WHICH HAS BEEN
HAPPENING THE PAST SEVERAL RUNS. QPF THROUGH 12Z FRI: 2-4.75" NORTH
BAY, 4-11" SIERRA, 6-11" SHASTA, 3-5" NORTH COAST (6-8" KINGS
RANGE), 1.50-5" CENTRAL COAST (UP TO 6" SANTA CRUZ/8.50" BIG SUR
MOUNTAINS), 1.50-4.50" SACRAMENTO VALLEY INTO THE FOOTHILLS, 1-3.50"
S TO N SJ VALLEY/MOST OF THE REST OF NRN CA, AND 1.75-7" FOR MOST OF
COASTAL SRN CA (UP TO 17" TRANSVERSE RANGE).
METEOROLOGICAL CONDITIONS (LONG TERM: FRI AM - MON AM)
MAIN UNCERTAINTY SURROUNDING THE LONG TERM FORECAST WINDOW CONTINUES
TO BE HOW QUICKLY AND WHERE THE WEAKENING LOW PRESSURE SYSTEM
DISSIPATES OVER CALIFORNIA ON FRIDAY INTO SATURDAY MORNING.
AFTERNOON FORECASTS PRIMARILY BLENDED IN THE LATEST NBM
PRECIPITATION WHICH KEPT REMNANT SHOWERS AROUND LONGER THAN THE
MORNING FORECAST.
THE SLOWER DISSIPATION OF THE LOW AND IT'S ACCOMPANYING SHOWERS
RESULTED IN A SLIGHT INCREASE IN QPF OF UP TO A QUARTER INCH OVER
THE NORTH COAST EXTENDING INLAND TO THE SHASTA DRAINAGE AS WELL AS
SOUTHERN CALIFORNIA.
RELATIVELY LOW FREEZING LEVELS (COMPARED TO THE PAST SEVERAL DAYS)
WILL ACCOMPANY THE DISSIPATING LOW PRESSURE SYSTEM, DROPPING TO <6K
FEET ACROSS MUCH OF THE FORECAST AREA (NORTH OF THE TRANSVERSE
RANGE). LEVELS ARE FORECAST TO RISE ONCE RIDGING BEGINS TO REBUILD
OVER THE AREA.
QPF GRAPHICS ARE AVAILABLE AT WWW.CNRFC.NOAA.GOV/QPF.PHP
AS/CH
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