Quantitative Precipitation Forecast
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FOUS30 KWBC 222244
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
643 PM EDT MON MAY 22 2017

...VALID 2243Z MON MAY 22 2017 - 12Z TUE MAY 23 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 E KGBK 25 ENE KVAF 20 SSE KBQX 20 NNE BYY 20 ESE CXO
10 SSW IER IER 25 WNW GTR 25 NE DNN RUQ 10 SSW PGV 20 NE NKT
25 SSW MRH 35 SE CRE 45 ESE CHS 20 NW LHW 11J 15 SE PNS KVOA
20 SW KIKT 30 SSW KMYT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WNW XCN 25 NW KHQI 15 N KGVX 10 ESE EFD 20 WSW DRI HKS
15 NNE ANB LZU 25 W 3J7 10 SW OPN GZH 10 ESE KVKY 30 W KMYT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SSE UZA MEB 20 S NCA 20 SE ILM 25 SE CRE 45 SSW MYR
30 ESE OGB 15 WNW CAE 30 SSE UZA.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SE KEIR 20 N KVQT 10 NNE KCRH 25 ENE 7R5 10 N ASD BIX
35 SSE BIX 20 NW KMIS 20 NNE S58.


2200 UTC UPDATE...

HAVE MADE SOME MINOR TWEAKS TO THE EXCESSIVE RAINFALL
OUTLOOK...WHICH INCLUDING PARING THE BACK (WESTERN) EDGES OF THE
AREAS ACROSS EASTERN TX BASED ON THE ACTIVITY HAVING SHIFTED OFF
TO THE EAST. HAVE ALSO ELONGATED THE SLIGHT RISK AREA FARTHER
NORTHEAST INTO A SLIVER OF WESTERN GA BASED ON THE OBSERVATIONAL
AND MODEL TRENDS...AS THE MORE RECENT CAM GUIDANCE SUPPORTS
WIDESPREAD CONVECTIVE ORGANIZATION INTO THE EVENING HOURS ALONG
THE FRONTAL ZONE. OVER THIS AREA...THE LOW-LEVEL FRONTOGENESIS
WILL BE AIDED BY A SUBTLE UPPER LEVEL JET STREAK TRAVERSING TN/KY.
ANOTHER MORE ENHANCED (SLIGHT) RISK WAS NOTED ACROSS NORTH-CENTRAL
TO NORTHEAST SC INTO SOUTHERN NC...AGAIN ALONG/NEAR THE LOW-LEVEL
FRONTAL ZONE WHERE THE SEA-BREEZE COMPONENT IS ALLOWING FOR A MORE
SOUTHERLY PRE-FRONTAL SURFACE FLOW AND THUS BETTER (MORE FOCUSED)
MOISTURE FLUX CONVERGENCE.

LASTLY...THE MODERATE RISK AREA WAS TRIMMED A BIT ON THE
NORTH-NORTHEAST PORTION BASED ON THE CURRENT (AND PROJECTED)
INSTABILITY GRADIENT...AS IT WOULD APPEAR THE HIGHEST DEEP-LAYER
CAPES (AND THUS RAINFALL RATES) WILL RESIDE GENERALLY SOUTH OF
LAKE PONTCHARTRAIN.

HURLEY



PREVIOUS DISCUSSION FOLLOWS...


MID TO UPPER TX COAST---CENTRAL GULF COAST/LOWER MS VALLEY INTO
THE SOUTHEAST

THERE WERE ONLY SOME MINOR CHANGES MADE TO THE PREVIOUS EXCESSIVE
RAINFALL POTENTIAL OUTLOOK FOR THE UPCOMING DAY 1 PERIOD FROM THE
MID TO UPPER TX COAST---EASTWARD ACROSS THE LOWER MS
VALLEY/CENTRAL GULF COASTAL REGION AND INTO THE SOUTHEAST. A BROAD
RISK REGION MAINTAINED IN THE VICINITY OF THE SURFACE FRONTAL
BOUNDARY THAT IS EXPECTED TO REMAIN NEARLY STATIONARY THIS
FORECAST FROM SOUTH TX EASTWARD ALONG THE CENTRAL GULF COAST AND
THEN NORTHEASTWARD INTO THE SOUTHEAST/SOUTHERN APPALACHIANS.
WITH PW VALUES EXPECTED TO REMAIN MUCH ABOVE AVERAGE IN THE
VICINITY OF THIS FRONT--1.5 TO 2+ STANDARD DEVIATIONS ABOVE THE
MEAN---AND STRONG LARGE SCALE LIFT ASSOCIATED WITH HEIGHT FALLS
PUSHING EASTWARD IN THE VICINITY OF THIS FRONT FROM SOUTH
TX---ALONG THE GULF COAST AND INTO THE SOUTHEAST---THERE IS A
STRONG MODEL SIGNAL FOR WIDESPREAD HEAVY TO LOCALLY EXCESSIVE
RAINFALL AMOUNTS.  THERE ARE STILL SOME SIGNIFICANT DIFFERENCES
WITH THE MAX QPF AXES AMONG THE MODELS.  THE FARTHER SOUTHWARD
AXES OF THE ARW---NMMB AND THEIR PARALLEL VERSIONS---ALONG WITH
THE NAM CONEST AND CMC GEM WERE PREFERRED OVER THE FARTHER
NORTHWARD GFS AND EC SOLUTIONS.  THE NAM AND GFS HAVE BEEN SHOWING
A SOUTHWARD TREND OVER THE PAST FEW RUNS WITH THEIR MAX QPF
AXIS---TOWARD THE FARTHER SOUTHWARD HI RES RUNS. THE
ECMWF---HOWEVER---HAS SHOWN THE OPPOSITE.  WHILE CONFIDENCE IS NOT
GREAT WITH THE SHORTER TERM DETAILS---EXPECT AN INITIAL AREA OF
HEAVY RAINS TO SPREAD EASTWARD MONDAY MORNING FROM COASTAL TX INTO
THE CENTRAL GULF COAST---PUSHING INTO THE SOUTHEASTERN U.S. LATER
MONDAY INTO MONDAY NIGHT.  IN THE WAKE OF THIS
ACTIVITY---ADDITIONAL CONVECTION MAY FIRE ALONG THE STATIONARY
FRONT FROM COASTAL TX INTO THE CENTRAL GULF COAST.  TRAINING OF
CELLS PARALLEL TO THE FRONT POSSIBLE AS MOIST WEST SOUTHWESTERLY
LOW LEVEL FLOW PERSISTS PARALLEL TO THIS FRONT INTO EARLY TUESDAY.
 WIDESPREAD 1-3" AREAL AVERAGE AMOUNTS DEPICTED DAY 1 ACROSS THESE
AREAS---WITH POTENTIAL FOR MAXIMA OF 5"+ WHERE TRAINING OF CELLS
OCCURS WITH BOTH ROUNDS OF ORGANIZED PRECIP.  SEE WPC`S MESOSCALE
PRECIPITATION DISCUSSION #0258 VALID UNTIL APPROXIMATELY 1400 UTC
FOR ADDITIONAL INFORMATION ON THE DEVELOPING CONVECTION ALONG THE
TX GULF COAST.


ORAVEC

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