995
FOUS30 KWBC 210057
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
757 PM EST SAT DEC 20 2025
DAY 1
VALID 01Z SUN DEC 21 2025 - 12Z SUN DEC 21 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA...
0100 UTC UPDATE: MINOR CHANGES MADE TO THE MARGINAL RISK AREA OVER
PARTS OF NORTHERN CA BASED ON THE LATEST GUIDANCE TRENDS, INCLUDING
THE MOST RECENT HREF AND RRFS QPF EXCEEDANCE PROBABILITIES. PER
BOTH OF THESE ENSEMBLES, RAINFALL RATES AOA 0.50"/HR BECOME MORE
LIKELY (PROBS AOA 50%) BETWEEN 06-07Z ACROSS PARTS OF THE OUTLOOK
AREA, WITH MORE WIDESPREAD AREAS >60% (ESPECIALLY OVER THE NORTHERN
SIERRA AND WESTERN FOOTHILLS) EXPECTED BETWEEN 09-12Z. THROUGH
12Z, BOTH HREF AND RRFS PROBABILITIES OF AT LEAST 3" OF RAINFALL
ARE >50% ACROSS THE OUTLOOK REGION, WITH 30-35% PROBS OF 5+ INCH
TOTALS OVER THE WESTERN SLOPES OF THE NORTHERN SIERRA, IN AND
AROUND BURN SCAR AREAS BETWEEN CASCADE AND MEADOW VALLEY.
HURLEY
PREVIOUS DISCUSSION...
STILL EXPECTING AREAS WITHIN THE NORTHERN SIERRA NEVADA TO RECEIVE
THE MOST APPRECIABLE PRECIPITATION GIVEN THE TRAJECTORY OF THE IVT
PULSE AND PERSISTENT 850-600MB MOISTURE FEED WITH ADDED UPSLOPE
COMPONENTS NEAR THE TERRAIN. GREATEST FLOOD CONCERNS LIKELY IN THE
ADJACENT FOOTHILLS ON THE WINDWARD SIDE OF THE SIERRA NEVADA.
HIGHEST PROBS FOR >5" ARE ACROSS THE I-80 CORRIDOR AT THE
CALIFORNIA/NEVADA BORDER WITH THE HIGHEST TERRAIN STILL LIKELY TO
BE SNOW, LIMITING THE THREAT FOR FLASH FLOODING FOR THE PERIOD TO
THAT OF A MARGINAL.
CAMPBELL/KLEEBAUER
DAY 2
VALID 12Z SUN DEC 21 2025 - 12Z MON DEC 22 2025
...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...
2030 UTC UPDATE: EXPANDED THE SLIGHT AND MODERATE RISK AREAS BASED
ON THE LATEST (12Z) GUIDANCE QPFS AND TRENDS. WITHIN THE MODERATE
RISK AREA, THERE ARE SEVERAL HOURS OF >50% HREF PROBABILITIES OF
AT LEAST 0.50"/HR RATES BETWEEN 12Z SUN AND 03Z MON, WHILE HREF
PROBABILITIES OF >8" WITHIN THE 24 HOUR DAY 2 PERIOD ARE >60% FOR
MUCH OF THE AREA.
HURLEY
PREVIOUS DISCUSSION...
A SIGNIFICANT UPTICK IN MOISTURE WILL BE SURGING INTO NORTHERN
CALIFORNIA DURING THIS PERIOD WITHIN THE REINFORCED ATMOSPHERIC
RIVER AND WILL LEAD TO WIDESPREAD HEAVY RAINFALL AND GREATER
THREAT FOR FLASH FLOODING, PARTICULARLY FOR PORTIONS OF THE SIERRA
NEVADA FOOTHILLS WHERE MULTI-DAY TOTALS OF 5-10" ARE FORECAST. A
MODERATE RISK AREA WAS RAISED FOR THIS PERIOD GIVEN MORE LOCATIONS
WILL BE AT RISK FOR RAPID RUNOFF AND POTENTIAL DEBRIS FLOWS. THE
AREAL EXTENT OF THE MODERATE WILL CONTINUE TO BE MONITORED AND MAY
BE ADJUSTED WITH FUTURE UPDATES.
CAMPBELL
DAY 3
VALID 12Z MON DEC 22 2025 - 12Z TUE DEC 23 2025
...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...
2030 UTC UPDATE: EXPANDED THE SLIGHT AND MODERATE RISK AREAS
SLIGHTLY, ESPECIALLY ON THE SOUTHERN PERIPHERY, BASED ON THE
LATEST (12Z) GUIDANCE QPFS AND TRENDS. THE SLIGHT RISK AREA NOW
INCLUDES THE FAR NORTHERN PORTIONS OF THE SAN JOAQUIN VALLEY AND
WITH A LITTLE BIT MORE OF THE CENTRAL SIERRA FOOTHILLS.
HURLEY
PREVIOUS DISCUSSION...
THE ONGOING ATMOSPHERIC RIVER WILL PERSIST WHILE SINKING A BIT SOUTHWARD
TOWARD CENTRAL CALIFORNIA, SPREADING RAINFALL FURTHER DOWN THE
SIERRA NEVADA RANGE AND ALONG THE COASTLINE. WITH THE REDUCTION OF
RAIN ON THE NORTHERN PERIPHERY THE THREAT FOR EXCESSIVE RAINFALL
WILL REMAIN AT A MARGINAL LEVEL. A MODERATE RISK WAS RAISED AGAIN
FOR MUCH OF THE AREA IDENTIFIED DURING THE DAY 2 PERIOD AND FOR
LOCATIONS A TOUCH TO THE SOUTH. THIS PART OF THE STATE IS EXPECTED
TO PICK UP ANOTHER 3+ INCHES WHICH WILL TIP THE 3 DAY ACCUMULATIONS
OVER 12 INCHES FOR SOME AREAS. ANY ADDITIONAL RAINFALL WILL LEAD TO
RUNOFF AND INCREASE THE POTENTIAL FOR SLOUGHING AND DEBRIS FLOW
ALONG THE FOOTHILLS/ADJACENT LOCATIONS.
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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