Quantitative Precipitation Forecast
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FOUS30 KWBC 230051
QPFERD

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

...VALID 01Z TUE MAY 23 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 WNW QT9 15 ENE KEHC 7R5 15 WNW AEX 20 NW GTR 15 SW RHP 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 S GSM 30 SW SRN 10 NNE KCMB 15 N ACP JAN 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 S NCA 10 SSW SUT 40 ENE CHS 25 N CHS 10 SE FLO 10 WSW 45J
SOP 10 NE OAJ 30 S NCA.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE 7R3 20 SSW GPT 40 NNE KMIS 20 SE BVE 15 NNW S58
10 SE SRN 15 SSE 7R4 20 NNE 7R3.


2200-0100 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 AND FAR WESTERN LA 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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