EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
430 AM EDT SUN MAY 28 2017

...VALID 12Z SUN MAY 28 2017 - 12Z MON MAY 29 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WSW PEO 20 N UNV MRB 10 WNW CHO 20 SSW HLX 25 W RHP 20 W TCL
35 SE ESF 15 SW GLS 50 SSW HBV 55 N MMAN 65 SSW MMPG 10 E DLF
10 WNW TPL 30 WSW TXK 35 ESE MKL 30 SSE FTK 30 ESE TDZ 15 S CWAJ
25 NW ERI 15 E CWPS IAG 15 NW ROC 15 WSW PEO.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 NNW DTN 40 SE UTA 35 WNW GTR 15 E JAS 10 W 11R 20 N LHB
30 NNW DTN.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
AFJ 15 SE CAK 20 W HZY 15 ESE ERI 30 NNW DUJ 15 SW FIG CBE
25 SSW W99 30 SE 48I 10 NNW 48I AFJ.


...SOUTHERN PLAINS / LOWER MISSISSIPPI VALLEY...

MULTIPLE MESOSCALE CONVECTIVE SYSTEMS...ALIGNED IN A QUASI
WEST-EAST FASHION EARLY SUN MORNING...CONTINUE A SLOW SOUTHWARD
PROPAGATION INTO A MORE THERMODYNAMICALLY FAVORED ENVIRONMENT
(UNTAPPED DEEP-LAYER INSTABILITY). THE ACTIVITY CONTINUES TO BE
FUELED ALONG AND SOUTH OF AN ELONGATED SURFACE FRONT...LYING ON
THE SOUTHERN PERIPHERY OF THE BEST UPPER LEVEL CONFLUENCE. THIS
FRONT WILL CONTINUE TO SPUR ADDITIONAL CONVECTIVE ACTIVITY DURING
THE DAY 1 PERIOD...AS IT BECOME REINFORCED LATER IN THE PERIOD
(00-12Z MON) AS THE UPPER LEVEL JET STREAK TO THE NORTH
STRENGTHENS TO 110+ KTS AT 250 MB (RATHER ROBUST AT THIS LATITUDE
FOR LATE MAY). THE INCREASING ENTRANCE REGION UPPER JET FORCING
(LOW-LEVEL FRONTOGENESIS/UPPER DIVERGENCE) WILL FAVOR THE MORE
WIDESPREAD...HEAVIER CONVECTION INTO EASTERN TX...NORTHERN
LA/SOUTHERN AR...AND NORTHERN MS LATER TODAY AND THIS EVENING...AS
THE ACTIVITY SLIDES CLOSER TO THE WESTERN GULF COAST LATER SUN
NIGHT. THE CONCERN WILL CONTINUE TO BE WITH TRAINING...AS THE SLOW
MOVING SURFACE BOUNDARY REMAINS MORE OR LESS PARALLEL TO THE MEAN
850-500 MB FLOW.

IN TERMS OF THE QPF...WPC CONTINUED TO LEAN TOWARD VARIOUS PIECES
OF THE CAMS...WRF-ARW/PARALLEL ARW IN PARTICULAR...WHICH CONTINUE
TO VERIFY MORE FAVORABLY WITH RESPECT TO THE SOUTHWARD PROPAGATION
OF THE CONVECTION AS WELL AS WITH THE UPPER BOUND AMOUNTS IN AREAS
MOST LIKELY TO SEE CELL TRAINING. IN TERMS OF AREAL-AVERAGE
RAINFALL...WPC NOTED A SWATH OF 1.5-2.0+ INCHES IN A RELATIVELY
NARROW CORRIDOR FROM EASTERN TX ENE THROUGH NORTHERN LA/SOUTHERN
AR AND WESTERN MS. GIVEN THE AFOREMENTIONED CONCERNS (SLOW MOVING
BOUNDARY...LIKELIHOOD OF TRAINING/BACK-BUILDING WITH THE UPWIND
PROPAGATION)...EXPECT LOCALLY HIGHER AMOUNTS OF 3-6+" AS
ADVERTISED BY THE MAJORITY OF HIGH-RES MODELS. WPC WILL INCLUDE A
"SLIGHT" RISK OF EXCESSIVE RAINFALL OVER THIS AREA IN THE NEW DAY
1 EXCESSIVE RAINFALL OUTLOOK (ERO).


...TENNESSEE VALLEY / OHIO VALLEY / WESTERN APPALACHIANS / LOWER
GREAT LAKES...

AS THE CLOSED MID-UPPER LEVEL LOW DROPS INTO THE UPPER MS VALLEY
DURING THE DAY 1 PERIOD...INCREASING DOWNSTREAM UPPER DIFFLUENCE
ALONG WITH THE ARRIVAL OF THE THE INITIAL UPPER SHORTWAVE/VORT
LOBE AND 850-700 MB WARM FRONTAL ARC WILL ALLOW FOR AN EXPANSION
OF SHOWERS AND TSTMS ACROSS THESE AREAS...ESPECIALLY WHERE THE
LOWER-LAYER FLOW (SW-WSW) CAN ENHANCE THE COVERAGE/AMOUNTS
OROGRAPHICALLY. DEEP-LAYER INSTABILITY WILL BE MODEST AT
BEST...WITH THE MUCAPES GENERALLY BETWEEN 1000-1500 J/KG. PER THE
HIGH-RES CAMS...THERE REMAINS A SIGNAL FOR LOCALLY HEAVY RAINFALL
(2-4+ INCHES) ACROSS NORTHEAST OH...WESTERN PA...AND NORTHERN WV
GIVEN THE AFOREMENTIONED FAVORABLE UPSLOPE FLOW AND ANOMALOUS
850-700 MB MOISTURE FLUX (AROUND 2 STANDARD DEVIATIONS ABOVE
NORMAL). FOR THIS REASON...AND CONSIDERING THE WET ANTECEDENT
SOILS/LOWER FFG VALUES...WILL INCLUDE A "SLIGHT" RISK OVER THESE
AREAS IN THE DAY 1 ERO.

HURLEY