791  
FOUS30 KWBC 290033  
QPFERD  
 
EXCESSIVE RAINFALL DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
833 PM EDT SUN MAY 28 2017  
   
..VALID 01Z MON MAY 29 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  
65 ESE PIL 20 SSE MMMA 45 SW MMNL 15 ESE DLF 15 ESE ECU  
20 WNW GRK 20 E ACT 25 SSW CRS 20 SW GGG 15 NNE BAD 20 SW ELD  
20 SW GLH 10 SW GLH 25 SSW TUP 20 WNW TCL 20 S MEI 15 N HDC KVNP  
15 S KCRH.  
 
MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM  
20 NE CYPQ 20 WNW PEO 15 SSE IPT 15 E HGR 10 SW OKV 25 SSE W99  
25 S EKN 10 N 48I 20 ENE PKB 10 SE ZZV OSU 25 NNW SGH 35 SSE FWA  
20 NW DFI 30 NNW PHN CWGD 20 WNW CWLS.  
 
SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM  
20 SW HDO 15 SE ERV 20 SSE TPL 35 NNE LHB 15 N OCH 25 S BAD  
40 W MLU 15 SE MLU 25 NW HEZ 30 ENE ACP 25 NW BPT 35 S 3T5  
50 SSE SSF 35 SSE COT 25 N LRD 25 WNW COT 20 SW HDO.  
 
SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM  
15 WNW MRB 10 NNW W99 20 SSE MGW 15 SE AFJ 15 WSW PIT 20 SE CAK  
BJJ 15 NNE MFD 15 SW LPR BKL CGF 20 ENE GKJ 10 ESE BFD  
35 WNW IPT 25 ENE UNV 15 WNW HGR 15 WNW MRB.  
 
   
..01 UTC UPDATE
 
 
NO MAJOR CHANGES FROM THE PREVIOUSLY ISSUED WPC EXCESSIVE RAINFALL  
THREAT OUTLOOK OTHER THAN TO SHIFT THE WPC THREAT AREAS OVER TX  
AND THE LOWER MS VALLEY SLIGHTLY SEWD AND TO SHRINK THE UPPER OH  
VALLEY/CENTRAL APPALACHIANS THREAT AREAS SO BOTH MORE CLOSELY  
MATCH LATEST RADAR TRENDS AND HRRR GUIDANCE.  
 
SCHICHTEL  
 
   
..15Z UPDATE
 
 
WE MADE A MINOR EXPANSION TO THE SLIGHT RISK AREA AFFECTING THE  
PIEDMONT / EASTERN SLOPES OF THE CENTRAL APPALACHIANS IN PARTS OF  
PA/WV/MD/VA. MESOSCALE PRECIPITATION DISCUSSION 280 DESCRIBES THE  
SCENARIO THAT WILL BEGIN TO UNFOLD THERE BY EARLY AFTERNOON.  
 
ELSEWHERE WE MADE SOME ADJUSTMENT TO THE SLIGHT RISK AREA OVER THE  
LOWER MISSISSIPPI VALLEY AND EASTERN TEXAS...SHIFTING IF FARTHER  
SOUTH AND WEST...BUT NOT QUITE INTO THE HEART OF THE TX HILL  
COUNTRY. CONFLUENT MID LEVEL FLOW / RIGHT ENTRANCE REGION DYNAMICS  
SHOULD SUPPORT AN ORGANIZED HEAVY RAIN EVENT OVER EAST TX INTO  
LOUISIANA THIS AFTERNOON PER RECENT HRRR AND OTHER GUIDANCE.  
FARTHER WEST AND SOUTH FROM SAN ANTONIO TO BROWNSVILLE THERE ARE  
QUESTIONS. POOR LOWER LEVEL LAPSE RATES AND RELATIVELY ILL-DEFINED  
DEEP LAYER FORCING MAY INHIBIT CONVECTIVE COVERAGE AND  
ORGANIZATION. AT THE SAME TIME...THERE ARE INDICATIONS OF DEEPER  
MOISTURE MOVING INTO THIS REGION NEAR PEAK HEATING AND  
BEYOND...AND SOME HI-RES MODEL SOLUTIONS SHOW SOME UPSCALE  
GROWTH...DRIVEN BY LARGE CAPE...SHOULD CELLS BE ABLE TO MAINTAIN  
THEMSELVES DESPITE THE POOR LOW LEVEL LAPSE RATES. GIVEN  
UNCERTAINTY...WE MAINTAINED MARGINAL RISK. -BURKE  
   
..PREVIOUS DISCUSSION
 
 
   
..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  

 
 
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