Quantitative Precipitation Forecast
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FOUS30 KWBC 212259
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
614 PM EDT WED JUN 21 2017

...VALID 2214Z 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
30 SE KGVX 10 SSW LBX 20 WNW SGR 25 ESE CLL 30 N UTS 30 SE GGG
25 SE BAD 35 SW MLU 10 NW HEZ 30 SW HKS 25 ESE GWO 30 ESE MKL
55 NNE MSL 10 NNW 4A9 10 NNW CCO 30 NNW ABY 15 S BGE 35 SSW AAF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 WNW PVW 35 SSE CVN 15 W CVS 40 NNE TCC 55 WNW GCK 10 NE BVN
20 SE EAU 20 WSW MNM 25 SE SUE 30 SE SBM 20 S PDC 20 WSW AIO HJH
15 ENE DDC PPA 10 WNW PVW.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 E KGVX 20 ENE LBX 10 SW IAH 20 ESE UTS 45 E OCH 10 SE IER
30 ESE ESF 20 WSW MCB 30 S JAN 40 ENE JAN 15 NNE CBM 30 SSE 1M4
20 NW ALX 30 E TOI ECP 50 SW PAM.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 SSW KVBS 10 E KXIH 20 NNE GLS 30 ENE IAH 15 SW JAS DRI
25 SSE ACP 10 W 7R4 20 SW KVNP.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
KMIS 20 N 1B7 20 ESE NEW 30 ENE HDC 35 N PIB 25 NE NMM
45 SSE TCL 15 SSW MGM 30 W OZR 10 S DTS 55 ENE KVOA.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 N KMIS 15 SSW GPT 25 S HBG 25 E PIB 50 SE MEI 30 NW GZH
15 SE GZH 10 SSE NSE 25 S NPA.


...2200 UTC UPDATE...

MADE A FEW MINOR CHANGES TO THE PREVIOUS OUTLOOK...MAINLY TO
ADJUST THE AREAS ACROSS THE GULF COAST REGION AND LOWER TN VALLEY
BASED ON THE LATEST MESOANALYSIS/CONVECTIVE TRENDS...DETERMINISTIC
AND PROBABILISTIC QPF FROM THE LATEST WPC OUTPUT AS WELL AS THE
OPERATIONAL AND ENSEMBLE GUIDANCE (PARTICULARLY HIGH-RES
CAMS)...AND THE LATEST FFG ALONG WITH THE NATIONAL WATER MODEL
BASED SOIL MOISTURE ANALYSIS AND FORECAST. THIS RESULTED IN A
SLIGHT WESTWARD SHIFT OF THE MARGINAL-SLIGHT-MODERATE OUTLOOKS
ACROSS THE UPPER TX COAST...WHILE ALSO NUDGING THE MARGINAL AND
SLIGHT AREAS A BIT FARTHER NORTH ACROSS NORTHERN AL ALONG THE AXIS
OF THE PREDOMINANT MOISTURE FEED EAST OF CINDY (I.E. WARM CONVEYOR
BELT) WHERE PWS WILL BE CLIMBING TO 2.25+ INCHES OVERNIGHT WHILE
THE LOW-LEVEL (ABOVE SURFACE LAYER) MOISTURE TRANSPORT
STRENGTHENS.

HURLEY


PREVIOUS DISCUSSION BELOW...


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

*SIGNIFICANT AND POSSIBLY LIFE THREATENING FLASH FLOODING REMAINS
LIKELY TODAY ACROSS PORTIONS OF SOUTHERN MS/AL INTO THE FAR
WESTERN FL PANHANDLE...AND THUS A HIGH RISK OF EXCESSIVE RAINFALL
WAS MAINTAINED ACROSS THIS REGION.*

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
WESTERN FL PANHANDLE...WITH 5-8" (LOCALLY AS HIGH AS 10") IN FAR
SOUTHEAST MS INTO FAR SOUTHERN AL AND THE 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 DRY LINE COMBINED WITH THE
LIKELIHOOD OF ISOLATED TO SCATTERED INTENSE CONVECTIVE
CORES...DOES SUPPORT AT LEAST SOME ISOLATED FLASH FLOOD RISK. NEAR
THE WARM FRONT SOME BRIEF TRAINING COULD LEAD TO A LOCALIZED FLASH
FLOOD THREAT AS WELL...ALTHOUGH COVERAGE AND MAGNITUDE OF THE
THREAT IS LOW. OPTED TO EXTEND A MARGINAL RISK ALONG THE EXPECTED
CONVECTIVE AXIS.

CHENARD

$$





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