174
FOUS30 KWBC 191556
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1056 AM EST FRI DEC 19 2025
DAY 1
VALID 12Z FRI DEC 19 2025 - 12Z SAT DEC 20 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA AND NEW ENGLAND...
THE AR CONTINUES TO SAG SOUTHWARD, REDUCE RESIDENCY TIME, AS WELL
AS GENERALLY WEAKENING IN FLUX INTENSITY. ALL FACTORS SUPPORT A
REDUCTION OF THE CATEGORY TO MARGINAL RISK FOR THE REMAINDER OF THE
DAY. ALSO, HAVE REMOVED THE NORTHERN PORTIONS WITHIN OREGON
WHERE EVEN THE NORTHERN EDGE OF THE AR PLUME HAS MOVED SOUTH
LIMITING RAINFALL TOTALS TO BELOW EXCESSIVE CONCERNS.
THINKING AND PLACEMENT OF THE MARGINAL RISK IN NEW ENGLAND REMAINS
ON TRACK; SO NO CHANGES WERE MADE FOR THIS UPDATE.
GALLINA
~~~~PRIOR DISCUSSIONS~~~~
..PACIFIC NORTHWEST
ONGOING ATMOSPHERIC RIVER WILL DRIFT SOUTHWARD WHILE SWIFT FLOW
ALOFT TRANSPORTS THE PLUME OF DEEP LAYER MOISTURE INTO PARTS OF
THE NORTHERN GREAT BASIN. IVT VALUES AT OR ABOVE 700 UNITS ARE
FORECAST TO COVER MUCH OF OREGON INITIALLY BEFORE IT WEAKENS AS
THE AXIS OF THE MOISTURE PLUME AND ASSOCIATED PRECIPITATION SETTLES
INTO NORTHERN CALIFORNIA. THE MARGINAL RISK WAS MAINTAINED FOR
SOUTHWEST OREGON AND NORTHERN CALIFORNIA, AS WELL AS THE SLIGHT
RISK OVER NORTHWEST CALIFORNIA. MINIMAL ADJUSTMENTS WERE MADE TO
ACCOUNT FOR THE LATEST QPF TRENDS AND WPC FORECAST.
..SOUTHERN NEW ENGLAND
LOCALLY HEAVY RAINFALL WILL BE POSSIBLE FOR PORTIONS OF THE
NORTHEAST DURING THIS PERIOD AS MOISTURE DRAWN NORTHWARD ENCOUNTERS
THE ADVANCING TROUGH OVER THE EASTERN STATES. WITH TIME THE
THE MOIST FLOW ALOFT BECOMES INCREASINGLY DIFFLUENT AND A SURFACE
WARM FRONT APPROACHES FROM THE SOUTH EARLY ON FRIDAY. WPC
DETERMINISTIC QPF IN THE 1.0 TO 1.4 INCH RANGE IS FORECAST ALONG
THE TRACK OF THE LOW. OFFSETTING THE POTENTIAL OF EXCESSIVE
RAINFALL BY LIMITING RAINFALL RATES/AMOUNT IS THE MEAGER
INSTABILITY EXPECTED TO BE IN PLACE. A MARGINAL RISK WAS MAINTAINED
FROM THE NEW YORK/CONNECTICUT/MASSACHUSETTS BORDER TO DOWNEAST
MAINE.
CAMPBELL/BANN
DAY 2
VALID 12Z SAT DEC 20 2025 - 12Z SUN DEC 21 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...
A RELATIVE LULL IN MOISTURE SURGES EXPECTED DURING THE MAJORITY OF
THIS PERIOD BEFORE THE NEXT STRONGER ATMOSPHERIC RIVER FROM THE
PACIFIC REACHES NORTHERN CALIFORNIA TOWARDS THE END OF DAY 2.
ALTHOUGH THERE MAY BE SOME OVERLAP IN HEAVY RAINFALL, THE AXIS OF
THE STRONGEST ON-SHORE WINDS AND THE GREATEST ON-SHORE MOISTURE
TRANSPORT LOOKS TO BE SOUTH OF THE AXIS OF THE PREVIOUS EVENT.
PRECIPITABLE WATER VALUES INCREASE TO BETWEEN 1.2 AND 1.4 INCHES
ALONG THE NORTHERN CALIFORNIA COAST NORTH OF SAN FRANCISCO SOUTH OF
THE OREGON/CALIFORNIA BORDER BY EARLY SATURDAY EVENING. GIVEN SUCH
HIGH SNOW LEVELS...THERE IS NOT A LOT OF CONCERN ABOUT
PRECIPITATION TYPE UNTIL THE MOISTURE LADEN FLOW REACHES THE
NORTHERN END OF THE SIERRA NEVADA RANGE (SAVE FOR A FEW MOUNTAIN
TOPS ALONG THE TRAJECTORY INLAND FROM THE COAST). THE URBAN CENTERS
BETWEEN SACRAMENTO TO SAN FRANCISCO WILL BE MORE AT PLAY THIS
PERIOD LEAD
CAMPBELL/BANN
DAY 3
VALID 12Z SUN DEC 21 2025 - 12Z MON DEC 22 2025
...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
NORTHERN CALIFORNIA...
THE ATMOSPHERIC RIVER WILL STRENGTHEN OVER THE NORTHERN HALF OF
CALIFORNIA RESULTING IN SCATTERED TO WIDESPREAD AREAS OF ENHANCED
RAINFALL OVERLAPPING MUCH OF THE SAME FOOTPRINT FROM THE DAY 2
PERIOD. THE LATEST GUIDANCE IS SUGGESTING DAILY ACCUMULATIONS OF 3
TO 7 INCHES, WITH 48 HOUR TOTALS NEARING 5 TO 9 INCHES. A SLIGHT
RISK IS IN EFFECT FROM THE WEST COAST TO MUCH OF THE SIERRA NEVADA
RANGE. THERE MAY BE A NEED FOR AN UPGRADE FOR PORTIONS OF THE
SIERRA NEVADA SHOULD GUIDANCE CONTINUE TO INCREASE OVER THIS AREA.
CAMPBELL
DAY 1 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/94EPOINTS.TXT
DAY 2 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/98EPOINTS.TXT
DAY 3 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/99EPOINTS.TXT
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