Quantitative Precipitation Forecast
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FOUS30 KWBC 210831
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
430 AM EDT WED JUN 21 2017

...VALID 12Z WED JUN 21 2017 - 12Z THU JUN 22 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 E KBQX 35 NNW 5R5 15 SSW JSO 15 W SHV 30 S MLU 10 N HEZ
15 ESE GWO 40 NE TUP 30 NE ANB 40 ESE LSF 10 NE TLH 45 SSE AAF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 ENE GLD 30 SSW LXN 15 E ODX 15 S OTG 25 SW IMT 10 S GOV
20 W AMN 20 S MRJ 10 NNW DBQ 30 E ADU HJH 15 ENE DDC PPA PVW
35 SSE CVN 40 NE TCC 25 NW SPD 30 ENE GLD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 E KGVX 10 SSE LVJ 30 ENE CXO 25 WNW POE 45 SE ESF 25 SW MCB
30 NNE MCB 35 NE MCB 40 SW GTR 35 N TCL 25 WNW MXF MGM DHN PFN
50 SW AAF.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SW KVBS 20 WNW BPT 20 ESE JAS 15 W LFT 20 W PTN 20 NE SRN
10 ESE SRN.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 WNW KIKT 15 ENE BVE 15 NE BVE 25 NNW HSA 20 NE PIB
20 ESE NMM 35 S TCL 35 SW MGM 35 E GZH 35 NNE CEW 35 NNW ECP
35 WSW PAM.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 N KMIS 40 S BIX 25 NNW GPT 55 WNW GZH 10 ESE GZH HRT
25 SSW HRT.


...RISK OF EXCESSIVE RAINS ASSOCIATED WITH MOISTURE FROM TROPICAL
STORM CINDY...

HEAVY RAINFALL IS LIKELY TO CONTINUE ALONG PORTIONS OF THE GULF
COAST REGION IN ASSOCIATION WITH TROPICAL STORM CINDY...WITH THE
THREAT SPREADING A BIT FURTHER INLAND AS WELL TODAY OVER PORTIONS
OF MS/AL. A BROAD PLUME OF TROPICAL MOISTURE IS ASSOCIATED WITH
THIS SYSTEM...WITH PWAT VALUES OF 2"+ EXPECTED OVER MUCH OF THE
SOUTHEAST BY THIS AFTERNOON...WITH VALUES AROUND 2.5" PROBABLE AS
WELL. IN FACT RECENT RAP RUNS ARE FORECASTING PWAT VALUES NEAR ALL
TIME RECORD MAXES ACROSS PORTIONS OF LA/MS/AL AND THE FL PANHANDLE
(ALTHOUGH THE FORECAST COULD BE A BIT OVERDONE). NEEDLESS TO SAY
THE ATMOSPHERE WILL BE RIPE FOR EFFICIENT WARM RAIN PROCESSES
CAPABLE OF PRODUCING HEAVY RATES EVEN WITHOUT ROBUST DEEP
CONVECTION. CONTINUES TO LOOK LIKE WE WILL SEE TWO SEPARATE AREAS
OF HEAVY RAINFALL...ONE ASSOCIATED WITH A CONVERGENCE AXIS WELL
NORTHEAST OF THE TROPICAL SYSTEM...AND ANOTHER CLOSER TO (ALTHOUGH
STILL NORTH OF) THE CENTER OF CINDY.

THE HEAVIEST RAINFALL OVER THE DAY 1 PERIOD APPEARS TO LIKELY BE
ASSOCIATED WITH THE CONVERGENCE AXIS AND FEEDER BAND WELL
NORTHEAST OF CINDY. ALREADY SEEING HEAVY RAINFALL IN THIS AREA
MOVING INTO PORTIONS OF SOUTHERN MS/AL AND THE FL PANHANDLE.
SHOULD SEE WAVES OF RAIN CONTINUE THROUGH THE DAY WITH STRONG LOW
LEVEL MOISTURE TRANSPORT PERSISTING. EXPECT THAT WE WILL SEE A
BROAD SHIELD OF STRATIFORM RAIN WITH EMBEDDED LOW TOPPED
CONVECTIVE CORES CAPABLE OF PRODUCING VERY HEAVY RAINFALL RATES.
THE THREAT SHOULD SLOWLY PROGRESS A BIT FURTHER INLAND THROUGH THE
DAY AS WELL...ALTHOUGH WOULD EXPECT THE INTENSITY TO GRADUALLY
WANE THE FURTHER NORTH YOU GO. AS CINDY PROGRESSES WEST THIS
MOISTURE TRANSPORT AXIS MAY TEND TO SLOWLY SHIFT WEST AS
WELL...WITH CONVECTION EVENTUALLY PROPAGATING A BIT BACK TOWARDS
THE NORTHEAST LATER IN THE DAY. SOME MODEL DIFFERENCES CONTINUE
WITH THE EXACT PLACEMENT OF THIS HEAVY RAINFALL AXIS AND ITS
INLAND EXTENT. STAYED AWAY FROM THE 12Z ECMWF...WHICH APPEARED TO
BE TAKING CINDY TOO FAR WEST AND THUS ALSO WAS WEST WITH THE HEAVY
RAINFALL. OF THE GLOBAL GUIDANCE THE 0Z GFS AND UKMET SEEMED TO
BEST MATCH OUR EXPECTED EVOLUTION...ALTHOUGH THE GFS WAS PROBABLY
TOO FAR INLAND WITH THE HIGHEST TOTALS...AND THINK THE UKMET IS
PROBABLY KEEPING THE HIGHEST TOTALS TOO CONFINED TO THE COAST.
OVERALL THE QPF FORECAST RELIED HEAVILY ON THE 0Z SUITE OF HIGH
RES MODELS. WPC QPF GENERALLY STAYED CLOSE TO A CONSENSUS OF THE
AVAILABLE HIGH RES GUIDANCE...WHICH ENDS UP CLOSEST TO THE AXIS
SHOWN BY 0Z NSSL WRF AND GEM REGIONAL. THE DAY 1 WPC QPF IS
CALLING FOR 3"+ FROM SOUTHEAST MS INTO SOUTHWEST AL AND THE FAR
WESTERN FL PANHANDLE...WITH 5-8" IN FAR SOUTHERN AL AND FAR
WESTERN FL PANHANDLE. THIS IS A BIT OF A SHIFT EAST FROM OUR
PREVIOUS FORECAST...AND BRINGS SOME HEAVIER TOTALS FURTHER INLAND.
AMOUNTS OF THIS MAGNITUDE ARE SUPPORTED BY ALL THE HIGH RES
GUIDANCE. AGAIN THE MAIN UNCERTAINTY IS NOT REALLY WITH THE
GENERAL MAGNITUDE OF AMOUNTS...BUT WITH THE AXIS OF HIGHEST
TOTALS. SOME CHANCE THE AXIS SHIFTS A BIT WEST OR EAST OF OUR
CURRENT FORECAST...WITH OUR CURRENT FORECAST FEATURING A PLACEMENT
IN THE MIDDLE OF AVAILABLE GUIDANCE.

SIGNIFICANT AND POSSIBLY LIFE THREATENING FLASH FLOODING REMAINS
POSSIBLE ACROSS PORTIONS OF SOUTHERN MS/AL INTO THE FAR WESTERN FL
PANHANDLE...AND THUS A HIGH RISK WAS MAINTAINED ACROSS THIS
REGION. THE MODERATE AND SLIGHT RISKS WERE EXTENDED A BIT FURTHER
INLAND OVER MS/AL.

THE SECOND AREA OF HEAVIER TOTALS IS FORECAST ALONG THE SOUTHERN
LA COAST INTO FAR SOUTHEAST TX TO THE NORTH OF CINDY`S
CIRCULATION. STILL SOME UNCERTAINTY WITH THE SPEED AND TRACK OF
CINDY WHICH WILL IMPACT THIS RAINFALL AXIS...WITH WPC FOLLOWING A
CONSENSUS...WHICH MATCHES WELL WITH THE OFFICIAL NHC TRACK. ONLY
REALLY LEANED AWAY FROM THE 12Z ECMWF (TOO FAR WEST) AND THE 0Z
HRW ARW (TOO FAR EAST)...OTHERWISE A BLEND OF THE GFS/UKMET AND
THE HIGH RES GUIDANCE WAS USED. LOOKING AT AMOUNTS UPWARDS OF 2-4"
THOUGH 12Z THURSDAY..WITH LOCALIZED AMOUNTS APPROACHING 6"
POSSIBLE. WILL MAINTAIN THE MODERATE RISK FOR FAR SOUTHEAST TX
INTO SOUTHERN LA GIVEN THE HIGH PWAT AIR AND LIKELIHOOD OF
LOCALIZED 5"+ AMOUNTS. DID HOWEVER TRIM THE WESTERN EXTENT OF THE
MODERATE RISK. THIS IS BASED ON A SLIGHT EASTWARD SHIFT IN THE
LATEST GUIDANCE AND THE OFFICIAL NHC TRACK.

...PLAINS INTO THE MS VALLEY AND GREAT LAKES...

LIKELY TO HAVE CONVECTION BREAK OUT TODAY ALONG THE DRY LINE FROM
THE TX PANHANDLE INTO THE CENTRAL PLAINS...WITH ADDITIONAL
CONVECTION ALONG/NORTH OF A WARM FRONT OVER THE MS VALLEY AND
GREAT LAKES AS LOW LEVEL MOISTURE TRANSPORT INCREASES INTO THIS
BOUNDARY. WPC QPF FOLLOWED CLOSE TO A BLEND OF THE HIGH RES
GUIDANCE ACROSS THESE REGIONS. NOT EXPECTING ANY ORGANIZED FLASH
FLOOD THREAT WITH THIS ACTIVITY. ALTHOUGH PWAT VALUES AROUND OR
JUST ABOVE 1 SD ABOVE AVERAGE ALONG THE RY LIEN COMBINED WITH THE
LIKELIHOOD OF ISOLATED TO SCATTERED INTENSE CONVECTIVE CORES...DOE
SUPPORT AT LEAST SOME ISOLATED FLASH FLOOD RISK. NEAR THE WARM
FRONT SOME BRIEF TRAINING COULD LEAD TO A LOCALIZED FLASH FLOOD
THREAT...ALTHOUGH COVERAGE AND MAGNITUDE OF THE THREAT IS LOW.

CHENARD

$$





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