959
FOUS30 KWBC 070901
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
500 AM EDT SUN JUN 07 2020
DAY 1
VALID 12Z SUN JUN 07 2020 - 12Z MON JUN 08 2020
...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL GULF COAST IN ASSOCIATION WITH CRISTOBAL...
...WIDESPREAD FLASH FLOODING EXPECTED, POTENTIALLY SIGNIFICANT AND
LIFE THREATENING ACROSS PORTIONS OF EASTERN LOUISIANA AND SOUTHERN
MISSISSIPPI...
..GULF COAST
CHANGES FROM THE PREVIOUS FORECAST INCLUDED A SLIGHT EXPANSION OF
THE MODERATE RISK ACROSS SOUTHERN MS AND INTO SOUTHERN PORTIONS OF
AL (INCLUDING MOBILE), WHILE ALSO INCLUDING A HIGH RISK ACROSS FAR
EASTERN LA INTO SOUTHERN MS. THE FORECAST TRACK FROM THE NATIONAL
HURRICANE CENTER WAS PRETTY CLOSE TO THE EARLIER FORECASTS WHICH
RESULTED IN FAIRLY MINOR ADJUSTMENTS IN TERMS OF TIMING AND
PLACEMENT WITH THE HEAVIEST QPF TODAY THROUGH SUNDAY NIGHT. WBC
QPF COMPRISED A MULTI-MODEL BLEND OF THE HIGH-RES CAMS ALONG WITH
THE OPERATIONAL AND EXPERIMENTAL NBM. THE RESULT WAS A SLIGHT
CONSTRICTION OF THE HEAVIER AMOUNTS THAT PREVIOUS FORECASTS HAD
INTO CENTRAL MS AND SOUTHEAST AR. THE HEAVIEST AREAL-AVERAGE
RAINFALL CONTINUES TO BE ACROSS EASTERN LA/SOUTHERN MS, I.E. 4 TO
7+ INCHES, ATTENDANT WITH THE STRONG MOISTURE TRANSPORT EAST OF
THE CENTER OF CRISTOBAL AND FAVORED REGION FOR SIGNIFICANT,
POTENTIALLY PROLONGED MOISTURE FLUX CONVERGENCE (WHERE 850 MB
MOISTURE TRANSPORT/MOISTURE FLUX ANOMALIES ARE OVER 5 STANDARD
DEVIATIONS PER THE SREF AND GEFS). PW VALUES CLIMBING BETWEEN
2.5-2.75+ INCHES WITH THE TALL/SKINNY INSTABILITY PROFILE WILL
LEAD TO OPTIMAL RAINFALL EFFICIENCY WITH DEEP WARM CLOUD DEPTHS.
ON AREA OF CONCERN IS THE POTENTIAL FOR MORE SUBSTANTIAL
(DIFFERENTIAL) DIURNAL HEATING AND STRONGER INSTABILITY LATER
TODAY GIVEN THE BREADTH OF CRISTOBAL'S CIRCULATION AND SOME
ENTERTAINMENT OF DRIER AIR IN BETWEEN MAIN BANDS. THIS COULD LEAD
TO A SPIKE OF HOURLY RAINFALL RATES WELL OVER 2 INCHES, POSSIBLY
>3 INCHES. ALSO, THE MAJORITY OF THE HIGH-RES CAMS DEPICT
PERSISTENT INFLOW BANDING ON THE EAST AND EVENTUALLY SOUTHEAST
SECTOR OF CRISTOBAL'S PATH, LEADING TO THE POTENTIAL OF
PERSISTENT, TRAINING CONVECTION ACROSS THE MODERATE AND ESPECIALLY
HIGH RISK AREAS OF EASTERN LA AND SOUTHERN MS TONIGHT INTO MONDAY
MORNING AS THE CENTER OF CRISTOBAL PASSES TO THE NORTH.
..NORTHERN ROCKIES
MAINTAINED THE MARGINAL RISK AREA ACROSS PORTIONS OF MT EAST OF
WHERE THE PRECIPITATION IS EXPECTED TO FALL AS SNOW. FAVORABLE
UPPER LEVEL DIFLUENCE AND ASSOCIATED DEEP-LAYER MOISTURE/THETA-E
TRANSPORT WILL COUPLE WITH SOME INSTABILITY (MUCAPES GENERALLY
UNDER 1000 J/KG) IN PRODUCING A LOCALIZED FLASH FLOOD THREAT,
ESPECIALLY IN AREAS WHERE THE RAIN EXACERBATES SNOW MELT.
..EASTERN DAKOTAS INTO THE UPPER MISSISSIPPI VALLEY
UPGRADED A PORTION OF THE MARGINAL RISK FROM YESTERDAY'S DAY 2 ERO
TO A SLIGHT FOR THE DAY 1 PERIOD, BASED ON THE INITIAL HEAVY
RAINFALL EARLIER THIS MORNING (WET ANTECEDENT SOILS) AND RENEWED
CONVECTION LATER THIS AFTERNOON/EVENING AND OVERNIGHT ASSOCIATED
WITH THE INCREASING DIVERGENCE ALOFT BEHIND THE RIDGE AXIS AND
ROBUST LOW-LEVEL MOISTURE/THETA-E TRANSPORT PER THE STRENGTHENING
LLJ. FOLLOWING THE MORNING ACTIVITY, EXPECT A SHORT REPRIEVE
DURING THE AFTERNOON WITH INSTABILITY (MUCAPE CLIMBING OVER 2000
J/KG) REBOUNDING THANKS TO DIURNAL HEATING. WITH PRECIPITABLE
WATER VALUES OVER 1.75 INCHES AIDED BY STRONG (>45KT) LOW-LEVEL
S-SW FLOW, LOW-LEVEL MOISTURE TRANSPORT/FLUX ANOMALIES CLIMB TO
OVER 5 STANDARD DEVIATIONS ABOVE THE NORM. MOREOVER, WEAKENING,
MORE NORTH-TO-SOUTH ORIENTED CORFIDI VECTORS COULD LEAD TO SOME
TRAINING OF CONVECTION OVERNIGHT. AREAL-AVERAGE QPF WITHIN THE
SLIGHT RISK AREA IS EXPECTED TO RANGE BETWEEN 1 AND 2.5"; HOWEVER,
SOME OF THE HIGH-RES CAMS SHOW LOCALIZED TOTALS OF 3-5+ INCHES.
MOREOVER, THE LATEST HREF 40KM NEIGHBORHOOD PROBABILITIES OF 3
HOURLY RAINFALL TOTALS EXCEEDING FFG PEAKING BETWEEN 30-40% WITHIN
THE SLIGHT RISK AREA BETWEEN 00-06Z MONDAY.
HURLEY
DAY 2
VALID 12Z MON JUN 08 2020 - 12Z TUE JUN 09 2020
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL
GULF COAST STATES NORTHWARD TOWARD THE MID MISSISSIPPI VALLEY...
..CENTRAL GULF STATES NORTHWARD TO THE MID-MISSISSIPPI VALLEY
MAINTAINED THE ON-GOING MODERATE RISK OF FLASH FLOODING FROM PARTS
OF LOUISIANA/MISSISSIPPI/ALABAMA NORTHWARD INTO ARKANSAS...WITH
ONLY MINOR MODIFICATIONS BASED ON THE LATEST CRISTOBAL TRACK
GUIDANCE. FLASH FLOODING CONCERNS ARE ALONG AND AHEAD OF
CRISTOBALS PATH AS RAINBANDS ROTATE NORTH AND THEN EASTWARD AROUND
THE CENTER. IN SOME CASES, THESE RAINS WILL BE FALLING OVER AREAS
WHICH HAVE DEALT WITH ROUNDS OF HEAVY RAINFALL PRIOR TO CRISTOBAL
AND MIGHT BE MORE PRONE TO RUN-OFF OR FLOODING CONCERNS. A SECOND
AREA IF CONCERN IS IN THE WAKE OF CRISTOBAL DUE TO THE POSSIBLE
FORMATION OF A QUASI-STATIONARY RAINBAND. THE FORMATION OF SUCH A
RAINBAND HAS BEEN SHOWN IN THE HIGH-RESOLUTION GUIDANCE, AND WOULD
BE IN A FAVORABLE AREA CONSIDERING INCREASING INSTABILITY AND
CONFLUENT LOW LEVEL FLOW. HOWEVER, CONFIDENCE IN WHEN OR EXACTLY
WHERE SUCH A BAND FORMS IS QUITE LOW AT THIS TIME RANGE. THE
ASSUMPTION IS THAT THE AREA WILL BE REFINED OVER THE NEXT FEW
FORECAST CYCLES.
..UPPER MIDWEST TO PARTS OF THE MISSOURI VALLEY
THERE WILL BE STRONG DYNAMIC SUPPORT FOR SLOW MOVING, EFFICIENT
RAIN PRODUCING CONVECTIVE ACROSS THE NORTHERN PLAINS AND INTO THE
UPPER MISSISSIPPI VALLEY..ESPECIALLY FROM MONDAY AFTERNOON INTO
EARLY TUESDAY. THE ATMOSPHERE SHOULD HAVE PRECIPITABLE WATER
VALUES AT OR ABOVE 1.75 INCHES IN PLACE AS A COLD FRONT AND
SYNOPTIC SCAL TROUGH APPROACHES. WITH TRAINING, BACKBUILDING AND
CONTINUED INFLUX OF DEEP MOISTURE...SEVERAL LOCATIONS COULD SEE
TORRIENTIAL DOWNPOURS AND 1 TO 3 INCHES OF RAINFALL IN A SHORT
PERIOD OF TIME OVER AREAS. GIVEN THAT 1- AND 3-HOUR FLASH FLOOD
GUIDANCE TENDS TO BE 1.75 INCHES OR GREATER, THINK THAT THERE
COULD BE SOME RUN-OFF CONCERNS.
BANN
DAY 3
VALID 12Z TUE JUN 09 2020 - 12Z WED JUN 10 2020
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE
MID-MISSISSIPPI VALLEY INTO PARTS OF THE UPPER MIDWEST...
CRISTOBAL, OF WHAT REMAINS OF CRISTOBAL, WILL BE ACCELERATING
NORTHWARD DURING THE PERIOD WHILE MOISTURE STREAMING NORTHWARD
AHEAD OF CRISTOBAL WILL BE APPROACHING AND INTERACTING WITH A COLD
FRONT AND SYNOPTIC SCALE TROUGH ADVANCING FROM THE WEST. RAINFALL
RATES SHOULD INITALLY BE TAPERING OFF AS CRISTOBAL MOVES FARTHER
AWAY FROM ITS SOURCE OF DEEP MOISTURE...WITH AMOUNTS ALSO
BEGINNING TO DIMINISH IN RESPONSE TO THE STORMS INCREASING FORWARD
SPEED. HOWEVER, THE APPROACH OF A SYNOPTIC SCALE TROUGH SHOULD
RESULT IN AN INCREASE IN AREAL COVERAGE OF PRECIPITATION AHEAD OF
THE FRONT AS WELL AS LOW- AND MID-LEVEL FRONTOGENESIS LEADING TO
AREAS OF ENHANCED RAINFALL RATES. THE MODELS WERE NOT HANDLING
THE INTERACTION VERY WELL, RESULTING IN FAIRLY LOW CONFIDENCE IN
THE DETAILS. HOWEVER, WITH ANOMALOUSLY DEEP MOISTURE AND
INCREASING DYNAMICS...STILL FELT A SLIGHT RISK AREA WAS WARRANTED.
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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