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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