880
FOUS30 KWBC 210030
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
830 PM EDT TUE OCT 20 2026
DAY 1
VALID 01Z WED OCT 21 2026 - 12Z WED OCT 21 2026
THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS LESS
THAN 5 PERCENT.
KLEEBAUER
DAY 2
VALID 12Z WED OCT 21 2026 - 12Z THU OCT 22 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST & FOUR CORNERS WEDNESDAY/WEDNESDAY NIGHT...
1900Z UPDATE: BASED ON THE 12Z GUIDANCE TRENDS, INCLUDING THE
LATEST HREF AND REFS QPF AND FFG EXCEEDANCE PROBABILITIES, WE HAVE
EXPANDED THE SLIGHT RISK ACROSS SOCAL AND THE CENTRAL CA COAST,
WHILE ALSO EXPANDING THE MARGINAL RISK AREA THROUGH A LARGER
PORTION OF THE CENTRAL VALLEY, AS OFTEN TIMES THE GUIDANCE
(PARTICULARLY THE HIGH-RES CAMS) OVERDO THE DOWNSLOPE DRYING
BETWEEN THE COASTAL AND SIERRA RANGES. INCORPORATED WWRF-ECMWF QPF
GUIDANCE, ALONG WITH THE LATEST (12Z) ECAIFS, WHEN DELINEATING THE
OUTLOOK BOUNDARIES.
A MODERATE RISK WITHIN THESE SLIGHT RISK AREAS IS NOT OUT OF THE
QUESTION. PW/IVT ANOMALIES ARE QUITE HIGH FOR THE TIME OF YEAR (5
TO 6 PLUS STANDARD DEVIATIONS ABOVE NORMAL PER THE LATEST NAEFS
ENSEMBLE SITUATIONAL AWARENESS TABLE (ESAT), WHILE THE LATEST ECMWF
EXTREME FORECAST INDEX OR EFI IS 0.9+ IN SPOTS WITH SHIFT-OF-TAILS
>2. STILL NOT CONVINCED HOWEVER THAT THE DEGREE OF DEEP-LAYER
INSTABILITY WILL SUPPORT EXCESSIVE SHORT-TERM RAINFALL RATES, AT
LEAST WITH ANY PERISTENCE OVER MORE THAN JUST ISOLATED AREAS,
GIVEN THE MODEST, TRANSIENT HREF AND REFS PROBABILITIES OF >0.50+
IN/HR RATES AND FAIRLY LOW PROBABILITIES OF >1.0+ IN/HR RATES.
HURLEY
PREVIOUS DISCUSSION BELOW..
..SOUTHWEST
ON WEDNESDAY/WEDNESDAY NIGHT, A DEEP LAYER CYCLONE MOVES TO POINT
CONCEPTION AND SCOOPS UP MOISTURE FROM THE TROPICS, FLINGING IT
INTO THE SOUTHWEST. A BROADENING ZONE OF 300-600 KG/MS OF
INTEGRATED VAPOR TRANSPORT ENVELOPS THE SOUTHWEST. NEAR THE COLD
LOW ITSELF, MU CAPE OF ~500 J/KG AND PRECIPITABLE WATER VALUES OF
1-1.3" WITH UP TO 30 KTS OF ONSHORE FLOW AT 850 HPA IS FORECAST,
WHICH WOULD SUPPORT HOURLY AMOUNTS TO 2" WHERE CELLS MANAGE TO
TRAIN OR BACKBUILD WITHIN THE TERRAIN. PER COORDINATION WITH
LOX/THE OXNARD CA FORECAST OFFICE, WENT AHEAD AND UPGRADED TO A
SLIGHT RISK FOR PORTIONS OF SOCAL, INCLUDING THE COASTAL RANGES
NORTH OF POINT CONCEPTION AND THE WESTERN TRANSVERSE RANGES TO ITS
EAST, INTO THE LOS ANGELES METROPOLITAN AREAS.
ACROSS PORTIONS OF THE SOUTHWEST, MU/ML CAPE IS FORECAST TO RISE TO
1000-3000 J/KG WITH LESSER AMOUNTS TO THE NORTH ACROSS THE GREAT
BASIN/ROCKIES, WITH PRECIPITABLE WATER VALUES RISING INTO 0.75-1.5"
RANGE. THE INGREDIENTS AVAILABLE ALONG WITH DETERMINISTIC GUIDANCE
QPF OUTPUT APPEAR SUFFICIENT TO MAINTAIN THE EXISTING SLIGHT RISK.
HOURLY RAIN AMOUNTS TO 2.5" WOULD BE POSSIBLE ACROSS PORTIONS OF
AZ, NM, AND THE FOUR CORNERS IN WIDELY SCATTERED TO SCATTERED
SPOTS DUE TO CELL TRAINING OR WHERE CELLS BACKBUILD OR MERGE.
URBAN AREAS, BURN SCARS, SLOT/BOX CANYONS, AND DRY WASHES/ARROYOS
WOULD BE THE MAIN AREAS OF CONCERN WITH THE HEAVY RAINFALL
ANTICIPATED.
ROTH
DAY 3
VALID 12Z THU OCT 22 2026 - 12Z FRI OCT 23 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST AND FOUR CORNERS REGION THURSDAY/THURSDAY NIGHT...
1900Z UPDATE: BASED ON THE LATEST GUIDANCE TRENDS, DID NOT MAKE
MANY CHANGES TO THE DAY 3 ERO, OUTSIDE OF EXPANDING THE SLIGHT
RISK SLIGHTLY. LATEST FIRST-GUESS FIELDS CONTINUE TO SUPPORT A
HIGH-END SLIGHT RISK EVENT, HOWEVER CANNOT RULE OUT A MODERATE RISK
AT SOME POINT ALONG AND EAST OF THE 4-CORNERS (INCLUDING THE SAN
JUAN MOUNTAINS), ALONG WITH AREAS EAST-NORTHEAST OF THE AZ SUN
CORRIDOR TO THE MOGOLLON RIM (AZ) AND GILA REGION (NM). LATEST QPF
TRENDS WITH THE RRFS ALONG WITH THE GLOBAL MODELS ON DAY 3 ARE A
BIT INCONCLUSIVE AT THIS POINT, AGAIN PREDICATED ON THE
DEPTH/DEGREE OF INSTABILITY THURS/THURS NIGHT.
HURLEY
PREVIOUS DISCUSSION BELOW..
THE SLIGHT RISK AREA REMAINS FOR PARTS OF THE SOUTHWEST/FOUR
CORNERS ON THURSDAY AS A DEEP MID/UPPER LEVEL LOW AND ACCOMPANYING
AMPLIFIED UPPER TROUGH MOVES FROM CA INTO THE GREAT BASIN. HEAVY
TO POTENTIALLY EXCESSIVE RAINFALL REMAINS A CONCERN GIVEN THE
MAGNITUDE OF THE TROPICAL MOISTURE BEING ADVECTED INTO THE REGION,
WITH INTEGRATED VAPOR TRANSPORT OF UP TO 600 KG/MS. DEEP SOUTHERLY
FLOW AHEAD OF THE APPROACHING TROUGH WILL ADVECT AN AIRMASS WITH
PRECIPITABLE WATER VALUES OF 1-1.5" INTO THE REGION, VERY HIGH BY
OCTOBER STANDARDS. FREEZING LEVELS WILL BE QUITE HIGH IN SOUTHWEST
CO, CLOSE TO THE MOUNTAIN PEAKS. MU CAPE IS FORECAST TO BE 1000+
J/KG IN EASTERN AZ EARLY ON. THE INGREDIENTS IN PLACE STILL SUGGEST
THAT AT LEAST LOCALLY SIGNIFICANT IMPACTS ARE A POSSIBILITY. HOURLY
RAIN AMOUNTS TO 2.5" ARE POSSIBLE GIVEN THE INGREDIENTS AVAILABLE.
THIS IS A HIGHER END SLIGHT RISK FOR PORTIONS OF SOUTHEAST AZ AND
SOUTHWEST CO. TRENDS WILL CONTINUE TO BE MONITORED AND CAN NOT
RULE OUT THE NEED FOR EMBEDDED MODERATE RISK AREA(S) AS WE GET
CLOSER TO THE EVENT. URBAN AREAS, BURN SCARS, SLOT/BOX CANYONS,
AND DRY WASHES/ARROYOS WOULD BE THE MAIN AREAS OF CONCERN WITH THE
HEAVY RAINFALL ANTICIPATED.
ROTH
DAY 4 AND DAY 5
VALID 12Z FRI OCT 23 2026 - 12Z SUN OCT 25 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST U.S. AND SOUTH FLORIDA ON SATURDAY/SATURDAY NIGHT...
20Z UPDATE: THE CURRENT SYNOPTIC PATTERN FOR BOTH THE SOUTHWESTERN
CONUS AND THE SOUTHEAST FL COAST MAINTAIN SIGNALS FOR ENHANCED
CONVECTIVE POTENTIAL AND THE PROSPECT FOR SCATTERED FLASH FLOOD
SIGNALS FOR EACH RESPECTIVE SETUP. BOTH SLGT RISKS ON D5 WERE
MAINTAINED, BUT ADJUSTED TO REFLECT THE LATEST QPF TRENDS. GUIDANCE
FOR FL IS KEYING ON THE IMMEDIATE COASTAL AREAS AS THE PRIMARY
POINT OF EMPHASIS, CORRELATING WITH THE URBAN CORRIDOR THAT TENDS
TO BE MORE PRONE TO FLASH FLOODING GIVEN THE MASS OF IMPERVIOUS
SURFACES. TIGHTENED THE SLGT RISK CLOSER TO THE COAST TO REFLECT
THE TREND OF CONVECTION LIKELY TIED RIGHT ALONG THE ATLANTIC COAST
WITH THE GREATEST PQPF SIGNATURE FROM PORT ST. LUCIE DOWN TO
NORTHERN MIAMI.
FOR THE SOUTHWEST U.S, THE THREAT WILL BE TIED TO THE ANOMALOUS
MOISTURE ADVECTION INTO THE AREA WITH THE BEST ASCENT LOCATED
WITHIN THE DOWNSTREAM DIFFLUENT SIGNATURE AHEAD OF THE BROAD ULL
FORMATION TO THE WEST. AS OF THIS TIME, THE ENSEMBLE MEAN QPF
DEPICTION WOULD NOTE AREAS ALONG AND EAST OF THE CONTINENTAL DIVIDE
AS THE MAIN AREAS OF CONCERN WITH SOME SIGNALS FOR LOCALLY 2+
INCHES, EVEN AT LEAD, FOR THE UPCOMING PATTERN. WILL NEED TO
MONITOR EXPANSE OF THE HEAVY RAIN FOOTPRINT AS GUIDANCE DIFFERS A
BIT ON THE EASTERN EXTENT OF THE HEAVIEST RAIN. THIS ALLOWED FOR
SOME ADJUSTMENT FOR BOTH THE SLGT AND MRGL RISKS OVER THE SOUTHERN
HIGH PLAINS OF TX WHERE SOME GUIDANCE LIMITS THE FAVORABLE ASCENT
FURTHER WEST WHICH WOULD NEGATE FLASH FLOOD CONCERNS OVERALL.
KLEEBAUER
.PREVIOUS DISCUSSIONS
SOUTHWEST US...
THE POTENTIAL REMAINS FOR LOCALLY HEAVY RAINFALL TO LINGER ON
THURSDAY INTO THURSDAY NIGHT AS THE AXIS A AN UPPER LEVEL TROUGH
REMAINS WEST OF THE REGION ACCORDING TO THE 20/00Z GFS AND ECMWF.
THAT LEAVES MUCH OF EASTERN AND CENTRAL NEW MEXICO WITH DEEP LAYER
SOUTHERLY FETCH OF MOISTURE. THE POTENTIAL FOR EXCESSIVE RAIN IS IN
A RELATIVE MINIMUM ON THURSDAY BEFORE ARRIVAL OF ADDITIONAL
MIDDLE- AND UPPER-LEVEL SHORTWAVE ENERGY REINVIGORATES THE CHANCES
OF HEAVY RAINFALL ON FRIDAY ACROSS PARTS OF THE HIGH PLAINS TO THE
LEE OF THE SOUTHERN ROCKIES. THE ADJUSTMENTS MADE TO THE MARGINAL
RISK AREA OF THURSDAY WAS MINIMAL WHILE A SLIGHT RISK AREA WAS
INTRODUCED IN THE PERIOD ENDING FROM FRIDAY AND INTO THE EARLY
MORNING HOURS OF SATURDAY.
SOUTH FLORIDA...
THE NUMERICAL GUIDANCE HAS BEEN SHOWING INCREASING MOISTURE
WITH EMBEDDED RAIN APPROACHING THE SOUTHERN FLORIDA PENINSULA FROM
THE SOUTHEAST. LATEST NUMERICAL GUIDANCE SUGGESTS LOCALLY HEAVY
RAINFALL COULD BEGIN AS EARLY AS FRIDAY BUT THE SIGNALS FOR GREATER
COVERAGE AND HIGHER RAINFALL AMOUNTS ARE FORECAST TO OCCUR ON
SATURDAY AS AN INVERTED TROUGH APPROACHES. GIVEN THE AMOUNT OF
URBANIZATION IN THE AREA COMBINED WITH LOCALLY HEAVY RAINFALL IN
THE AREA DURING THE PAST WEEK...OPTED FOR A SLIGHT RISK AT THIS
POINT ON SATURDAY.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page