Quantitative Precipitation Forecast
Issued by NWS

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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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