488
FOUS30 KWBC 180816
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
416 AM EDT SUN OCT 18 2026
DAY 1
VALID 12Z SUN OCT 18 2026 - 12Z MON OCT 19 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
SOUTH FLORIDA...
SOUTH FLORIDA...
A SECONDARY COLD FRONT WILL MAKE ITS WAY SOUTHWARD ACROSS SOUTH
FLORIDA TODAY RESULTING IN REDEVELOPMENT OF THUNDERSTORMS. SOME OF
THE STORMS WILL BE CAPABLE OF PRODUCING LOCALIZED DOWNPOURS OVER
URBANIZED AREAS. AFTER THE RAINFALL IN THE PERIOD PRIOR TO THE
START OF THE DAY 1 PERIOD...THE AREA MAY BE MORE PRONE TO FLASH
PONDING AND EXCESSIVE RAIN, HENCE THE MARGINAL RISK IS MAINTAINED.
BANN
DAY 2
VALID 12Z MON OCT 19 2026 - 12Z TUE OCT 20 2026
THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS LESS
THAN 5 PERCENT.
MOST OF THE GUIDANCE FROM THE 18/00Z CYCLE CONTINUES TO KEEP THE
SYSTEM FAR ENOUGH AWAY FROM THE EAST COAST TO KEEP THE EXCESSIVE
RAINFALL THREAT OFF-SHORE. EVEN SO...IT SHOULD BE ACKNOWLEDGED
THAT THE PROBABILITY OF EXCESSIVE RAINFALL IS PROBABLY NOT ZERO
PERCENT BUT NOT TO THE LEVEL OF RE-INTRODUCING A MARGINAL RISK
AREA.
BANN
DAY 3
VALID 12Z TUE OCT 20 2026 - 12Z WED OCT 21 2026
THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS LESS
THAN 5 PERCENT.
..SOUTHWEST
THE ATMOSPHERE STILL DOESN'T APPEAR TO BE SUFFICIENTLY SATURATED
WITH 0.75 INCHES TO 1 INCH NOR TERRIBLY UNSTABLE WITH ONLY A FEW
HUNDRED J/KG OF CAPE FORECAST BY THE 00Z GFS. AS A RESULT...DID NOT
OUTLOOK A MARGINAL RISK IN THIS PART OF THE COUNTRY.
BANN
DAY 4 AND DAY 5
VALID 12Z WED OCT 21 2026 - 12Z FRI OCT 23 2026
..SOUTHWEST
ON WEDNESDAY/WEDNESDAY NIGHT, A DEEP LAYER CYCLONE APPROACHES
SOCAL AND SCOOPS UP MOISTURE FROM A DYING TRUDY AND FLINGS IT INTO
THE SOUTHWEST. NEAR THE COLD LOW ITSELF, MU CAPE OF 250-500 J/KG
AND PRECIPITABLE WATER VALUES OF 1-1.3" WITH UP TO 30 KTS OF
ONSHORE FLOW AT 850 HPA IS FORECAST. THERE'S ENOUGH OF A HEAVY RAIN
SIGNAL FOR A MARGINAL RISK FOR THE TRANSVERSE AND PENINSULAR
RANGES, WHICH IS THERE TO HELP COVER BURN SCAR CONCERNS. IN AND
NEAR THE FOUR CORNERS, MU CAPE IS FORECAST TO RISE TO 500-750
J/KG, PRECIPITABLE WATER VALUES OF 0.75-1.25" ARE ANTICIPATED. THE
INGREDIENTS AVAILABLE ALONG WITH DETERMINISTIC GUIDANCE QPF OUTPUT REMAIN
WET ENOUGH FOR A MARGINAL RISK, THOUGH THE HIGHER TOTALS SEEN
24 HOURS AGO HAVE COME DOWN A BIT, POSSIBLY DUE TO A ~6 HOUR SLOW
DOWN/WESTWARD SHIFT OF THE OVERALL SYSTEM WHEN COMPARED TO THIS
TIME YESTERDAY. HOURLY RAIN AMOUNTS TO 2" WOULD BE POSSIBLE ACROSS
PORTIONS OF AZ, NM, AND THE FOUR CORNERS IN ISOLATED TO WIDELY
SCATTERED SPOTS.
FOR THURSDAY/THURSDAY NIGHT, THE SYSTEM SHIFTS EASTWARD ACROSS
SOUTHWEST AND GREAT BASIN/INTERMOUNTAIN WEST INTO PORTIONS OF THE
SOUTHERN HIGH PLAINS, WITH SIMILAR MOISTURE AND INSTABILITY IN
TOW. THE GUIDANCE ADVERTISES LOCAL TOTALS IN THE 2-3" RANGE, AND
HOURLY RAIN AMOUNTS TO 2" REMAIN POSSIBLE. THE MOUNTAINS OF SOCAL
APPEAR TO HAVE ENOUGH MOISTURE/INSTABILITY LEFT AND GUIDANCE QPF
SIGNAL TO INTRODUCE A MARGINAL RISK THERE WITH THE MARGINAL RISK
ACROSS THE INTERIOR WEST SHIFTING EASTWARD. IT IS POSSIBLE THAT
THE RISK LEVELS COULD INCREASE AS WE MOVE CLOSER TO THIS WEATHER
SETUP -- PARTICULARLY IF INSTABILITY TRENDS REVERSE/INCREASE
-- BUT THE SLOWING TREND IN THE GUIDANCE WITH THIS SYSTEM
INTRODUCES ENOUGH UNCERTAINTY NOT TO DO GO WITH A RISK LEVEL
BEYOND MARGINAL EITHER DAY AT THE PRESENT TIME.
ROTH
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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