960
AGUS76 KRSA 251631
HMDRSA
HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
830 AM PST THU DEC 25 2025
...ANOTHER ATMOSPHERIC RIVER BRINGING MODERATE TO HEAVY
PRECIPITATION WITH HEAVY SNOW TO THE FORECAST REGION AND INTO
TOMORROW...
...RETURN TO DRY WEATHER OVER THE WEEKEND AS RIDGING BUILDS OVER THE
WESTERN US...
METEOROLOGICAL CONDITIONS (THU AM - WED AM)
PRECIPITATION BEGAN SPREADING INLAND OVERNIGHT LAST NIGHT WITH BANDS
OF HEAVY PRECIPITATION IMPACTING NUMEROUS LOCATIONS ACROSS
CALIFORNIA IN ASSOCIATION WITH THE NEXT ATMOSPHERIC RIVER. CURRENT
RADAR IMAGERY SHOWS LIGHT TO MODERATE PRECIPITATION SPREADING ACROSS
THE NORTH COAST WITH HEAVIER PRECIPITATION EXTENDING SOUTHWEST TO
NORTHEAST FROM THE CENTRAL COAST/POINT CONCEPTION THROUGH THE
CENTRAL VALLEY AND INTO THE SIERRA WHERE THE MOISTURE PLUME AND COLD
FRONT EXTEND INLAND. PRECIPITATION FORECASTS WERE INCREASED WITHIN
THE IMMEDIATE 6-HOUR WINDOW WHERE HEAVY BANDING SETUP IN THE EARLY
MORNING HOURS, FROM SANTA CRUZ/MONTEREY BAY INLAND TO SACRAMENTO
COUNTY AND THE SIERRA AROUND THE I-80 CORRIDOR.
THE MOISTURE PLUME IS FORECAST TO SWING AROUND POINT CONCEPTION OVER
THE NEXT FEW HOURS, SPREADING SOUTHWESTERLY MOISTURE FLUX ACROSS THE
WESTERN TRANSVERSE RANGE IN SANTA BARBARA AND VENTURA COUNTIES.
WHILE THIS ORIENTATION IS EFFICIENT FOR UPSLOPE MOISTURE FLUX IN
THESE AREAS, THIS ATMOSPHERIC RIVER IS NOT AS STRONG AS YESTERDAY'S,
BRINGING MODERATE STRENGTH IVT MAGNITUDES (~500 UNITS) WITH A MORE
SOUTHWESTERLY COMPONENT ACROSS THE SOCAL BIGHT. WITH THAT BEING
SAID, HIGHER ELEVATIONS ACROSS THE TRANSVERSE RANGE ARE CURRENTLY
FORECAST TO RECEIVE AN ADDITIONAL 4 TO 6 INCHES OVER THE NEXT 48-
HOURS WITH LOCALIZED HEAVIER AMOUNTS WHERE CONVECTIVE FEATURES
INITIATE AND TRACK. WITH LOCALIZED CONVECTION EXPECTED TO BE
EMBEDDED WITHIN THE PRIMARY MOISTURE PLUME, RAIN RATES MAY APPROACH
1+ INCH/HR, EXTENDING THE FLASH FLOOD RISK THROUGHOUT THE REST OF
TODAY AND INTO TOMORROW ACROSS SOUTHERN CALIFORNIA.
THE MOISTURE PLUME WILL ALSO EXTEND INLAND ACROSS THE SAN JOAQUIN
VALLEY AND INTO THE CENTRAL AND SOUTHERN SIERRA NEVADA BRINGING
MODERATE AR CONDITIONS TO THE SIERRA FOOTHILLS. WITH THIS ADDITIONAL
AR ACTIVITY OVER THE SIERRA, 4-6 INCHES OF ADDITIONAL PRECIPITATION
IS FORECAST OVER THE NEXT 48-HOUR.
LOOKING FURTHER NORTH, GUIDANCE CURRENTLY SUGGESTS A SECONDARY PULSE
OF ENHANCED IVT (>500 UNITS) PUSHING INLAND OVER THE BAY AREA AND
NORTH COAST BETWEEN 00 AND 03Z ON THE 26TH (THIS EVENING). THIS WILL
FUNNEL ANOTHER BRIEF ROUND OF ELEVATED AR CONDITIONS ACROSS THE
NORTH COAST AND NORTHERN SIERRA. THE ORIENTATION OF THIS ADDITIONAL
PULSE (SOUTH/SOUTHEASTERLY) WILL LIKELY FAVOR PRODUCTIVE UPSLOPE
MOISTURE FLUX OVER THE SHASTA DRAINAGE AND NORTHERN SIERRA. IN
COMBINATION WITH THE MAIN MOISTURE PLUME, THE PARENT LOW PRESSURE
SYSTEM ASSOCIATED WITH THIS EVENT WILL PINWHEEL OFF THE NORCAL
COAST, SPREADING SHOWER ACTIVITY INLAND THROUGHOUT THE DAY AND INTO
TOMORROW. THIS SCENARIO IS FORECAST TO BRING 3-6+ INCHES ACROSS THE
NORTHERN SIERRA AND SHASTA DRAINAGE, 1-3 INCHES ACROSS THE NORTH
COAST AND, GENERALLY, <1 INCH TO LOCATIONS IN THE SACRAMENTO VALLEY
WITH HIGHER LOCALIZED ACCUMULATIONS IMPACTED BY CONVECTION.
THINGS ARE FORECAST TO BEGIN TAPERING OFF ON SATURDAY WITH LIGHT
REMNANT SHOWER ACTIVITY BEFORE RIDGING BEGINS TO BUILD INTO NEXT
WEEK AND DRIVE A RETURN TO DRY CONDITIONS.
FREEZING LEVELS HAVE LOWERED SINCE YESTERDAY MORNING TO ~5.5 TO 6K
FEET ACROSS THE SIERRA RESULTING IN WINTER CONDITIONS AND TREACHEROUS
TRAVEL INTO THIS MORNING. FREEZING LEVELS WILL REMAIN AROUND 6K FEET
IN THE NORTHERN SIERRA, ~7K FEET IN THE SOUTHERN SIERRA, AND 8K FEET
ACROSS SOUTHERN CALIFORNIA THROUGHOUT THE REMAINDER OF THE EVENT
BEFORE RISING SUBSTANTIALLY (12K+ FEET) UNDER THE BUILDING RIDGE.
PLEASE NOTE: THIS PRODUCT MAY NOT BE ROUTINELY UPDATED.
PLEASE REFER TO THE FOLLOWING PRODUCT ISSUED BY THE CNRFC
WWW.CNRFC.NOAA.GOV/DAILY-BRIEFING FOR A GRAPHICAL SUMMARY OF
WEATHER AND HYDROLOGIC CONDITIONS.
QPF GRAPHICS ARE AVAILABLE AT WWW.CNRFC.NOAA.GOV/QPF.PHP
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