013
FOUS30 KWBC 170828
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
328 AM EST MON NOV 17 2025
DAY 1
VALID 12Z MON NOV 17 2025 - 12Z TUE NOV 18 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF
SOUTHERN CALIFORNIA...
A VIGOROUS MID-LEVEL WAVE (INITIALLY CENTERED NEAR 39.9N, 125.5W
AT THE START OF THE FORECAST PERIOD) WILL MIGRATE SOUTH-
SOUTHEASTWARD ALONG THE CALIFORNIA COAST TODAY WHILE CUTTING OFF
FROM WESTERLIES FARTHER NORTH. AS THIS OCCURS, STRONG ASCENT
(ASSOCIATED WITH AREAS OF 0.3-0.6 INCH/HR RAIN RATES IN NORTHERN
CALIFORNIA THIS MORNING) WILL SPREAD SOUTHEASTWARD ALONG A COLD
FRONT AND ALSO WITHIN A ROBUST UPSLOPE REGIME ON THE WESTERN SIDES
OF THE SIERRA. 1-1.2 INCH PW VALUES NEAR THE COAST AND AFOREMENTIONED
SYNOPTIC FACTORS WILL FOSTER SEVERAL AREAS OF 1-2 INCH RAINFALL
TOTALS, WITH LOCALLY HIGHER AMOUNTS POSSIBLE ACROSS THE TRANSVERSE
RANGES OF SOUTHERN CALIFORNIA.
THE AFOREMENTIONED FRONT WILL RESULT IN A FOCUSED AXIS OF HEAVY
RAIN THAT WILL TRANSLATE FROM NORTH TO SOUTH ALONG THE SOUTHERN
CALIFORNIA COAST. ACROSS THE SLIGHT RISK AREA, THIS HEAVY RAINFALL
WILL OCCUR OVER BOTH SENSITIVE LOCALES (FROM RECENT BURN SCARS AND
DEBRIS FLOWS) AND URBAN/HYDROPHOBIC SURFACES. THE GREATEST
CONCENTRATION OF FLASH FLOOD RISK WILL LIKELY OCCUR ACROSS THE
TRANSVERSE RANGES AND ADJACENT AREAS OF LOS ANGELES METROPOLITAN
AREA THROUGH TONIGHT.
OUTSIDE OF THIS AREA, MODELS INDICATE VERY ISOLATED, BUT SLOW-
MOVING CONVECTIVE ACTIVITY BENEATH THE UPPER LOW CENTER ACROSS
NORTHERN AND CENTRAL CALIFORNIA, WITH HEAVY RAINFALL POTENTIALLY
FALLING OVER SOAKED GROUND CONDITIONS AND BURN SCARS. ISOLATED
FLASH FLOOD POTENTIAL CANNOT BE RULED OUT HERE.
LASTLY, THE CUTTING OFF UPPER LOW WILL SPREAD STRONG MID/UPPER
DIFLUENCE ACROSS THE LOWER COLORADO RIVER VALLEY ESPECIALLY IN THE
03-12Z TIMEFRAME. MODELS ARE CONSISTENT IN DEVELOPING AT LEAST ONE
OR TWO BANDS OF CONVECTIVE STRUCTURES THAT DRIFT NORTHWARD ACROSS
THE AREA FAIRLY QUICKLY, BUT ALSO RESULT IN LOCALIZED TRAINING. ONE
OR TWO INSTANCES OF FLASH FLOODING CANNOT BE RULED OUT IN THIS
REGIME.
COOK
DAY 2
VALID 12Z TUE NOV 18 2025 - 12Z WED NOV 19 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST AND LOWER GREAT BASIN...
MAINTAINED THE PREVIOUS;Y ISSUED MARGINAL RISK AREA OVER PORTIONS
OF ARIZONA WITH LITTLE NEED FOR MORE THAN COSMETIC CHANGES IN
DEFERENCE TO THE MODEL GUIDANCE. A CLOSED LOW WITHIN A BROADER
TROUGH DIGS SOUTHWARD ALONG THE THE WEST COAST OF THE US AND THEN
STARTS TO MOVE INLAND LATE. THE OVERALL SYNOPTIC PATTERN SEEMS TO
BE HANDLED COMPARABLY BY THE ECMWF/GFS AND UK MODELS FOR MUCH OF
DAY 2 BUT SOME OF THE SUBTLE DIFFERENCES IN THE DETAILS RESULT IN
NON-NEGLIGIBLE DIFFERENCES IN QPF AND THE ATTENDANT RISK OF
EXCESSIVE RAINFALL.
PRECIPITABLE WATER VALUES GET NEAR 2 STANDARD DEVIATIONS ABOVE NORMAL
FOR THIS TIME OF YEAR IN SOUTHERN-WESTERN AZ AND MOST-UNSTABLE
CAPE VALUES CLIMB ABOVE 500 J/KG SOUTH OF THE MOGOLLON RIM AND INTO
THE DESERTS AND PHOENIX METRO. THIS WILL MAINTAIN THE RISK OF
ELEVATED (0.50"+) HOURLY RAINFALL RATES TUE-TUE NIGHT AS NOTED FROM
THE RRFS EXCEEDANCE PROBABILITIES (THROUGH 00Z WED), WHILE ALSO
IMPLIED FROM THE 16/12Z RRFS 3-HOURLY QPFS. MUCH LIKE THE MODELS
FROM SUNDAY AFTERNOON...THE 24HR QPF GUIDANCE FROM THE 17/00Z MODEL
CYCLE HAS COME UP. AT THIS POINT THERE IS STILL NOT ENOUGH
CONFIDENCE FROM A DURATION PERSPECTIVE TO UPGRADE TO A SLIGHT RISK
OVER THE LOWER TERRAIN SOUTH OF THE MOGOLLON RIM, WHICH WOULD
CONCEIVABLY INCLUDE THE PHOENIX AREA, BUT THE POTENTIAL TO DO SO
WILL EXIST OVER THE NEXT DAY OR SO. THE MACHINE-LEARNING FIRST
GUESS FIELDS ALSO HIGHLIGHT PART OF THE MARGINAL RISK AREA WITH
SOME SPOTTY 5 TO 10 PERCENT OF EXCEEDING FLASH FLOOD GUIDANCE. AT
THIS POINT...THE MACHINE-LEARNING COVERS ONLY THE FIRST HALF OF DAY
2...SO THE UPCOMING DAY SHIFT WILL HAVE A COMPLETE LOOK AT THE
OBJECTIVE GUIDANCE FOR THE DAY 2 PERIOD.
BANN
DAY 3
VALID 12Z WED NOV 19 2025 - 12Z THU NOV 20 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTH CENTRAL TEXAS TO A PORTION OF THE ARKANSAS RIVER VALLEY...
A MID- AND UPPER-LEVEL TROUGH WILL BE MAKING ITS WAY EASTWARD
ACROSS PORTIONS OF THE SOUTHERN GREAT BASIN ON WEDNESDAY AND INTO
EARLY THURSDAY. EAST OF THAT SYSTEM...LOW LEVEL MOISTURE WILL START
TO BE DRAWN NORTHWARD WITH DEWPOINTS IN THE 60S BY WEDNESDAY AFTERNOON
WHICH SHOULD HELP FEED SHOWERS AND THUNDERSTORMS FROM THE AFTERNOON
INTO WEDNESDAY NIGHT/EARLY THURSDAY MORNING. MOST UNSTABLE CAPE
PUSHES 1000 J PER KG AND PRECIPITABLE WATER VALUES IN EXCESS OF
1.5 INCHES BECOMES ESTABLISHED FROM PARTS OF SOUTH-CENTRSL TEXAS
INTO EASTERN OKLAHOMA AND WESTERN ARKANSAS. BASED ON THE
GEFS...THE PRECIPITABLE WATER AXIS IS ROUGHLY BETWEEN 2 AND 2.5
STANDARDIZED ANOMALIES ABOVE CLIMATOLOGY FOR THIS TIME OF YEAR.
BASED ON THAT COMBINATION...SUSPECT LOCALLY HEAVY RAINFALL RATES
ARE POSSIBLE. THERE HAS BEEN A TENDENCY FOR THE UPPER TROUGH TO
SLOW ITS FORWARD SPEED WITH A SIMILAR DELAY IN CONVECTION
INITIATION. WITH THE EVENT SPANNING INTO THURSDAY WITH BROADER
AREAL COVERAGE AND AN INCREASING RISK OF EXCESSIVE RAINFALL (SEE
WPC MEDIUM RANGE GRAPHICS AND DISCUSSIONS FOR FURTHER
DETAILS)...OPTED TO MAINTAIN THE MARGINAL RISK ON THE UNCERTAINTY
OF TIMING.
BANN
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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