Quantitative Precipitation Forecast
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160
FOUS30 KWBC 190025
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
824 PM EDT TUE APR 18 2017

...VALID 01Z WED APR 19 2017 - 12Z WED APR 19 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 WSW FNB 20 SSW HJH 20 SSE AUH 20 S FET 25 WSW DSM 10 E AWG
15 SSE MUT 35 W EOK 30 SSW LWD FNB 30 WSW FNB.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 N KBBF 10 NW 5R5 15 NNE SGR 10 SSE IAH 10 NE BPT 20 SSW KVBS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 NE DBN 30 SE ATL 15 SW FTY VPC 25 WSW CHA 40 S MQY 10 SW BNA
25 NNE MQY 30 S EKQ 15 NNW 1A5 20 SW AVL 30 E GRD 25 ESE SSC
30 SW MYR 40 ESE CHS 10 NW HXD 10 SE JYL 40 NE DBN.


19/01Z UPDATE...
CHANGES TO PREVIOUS OUTLOOK AREAS WERE RELATIVELY MINOR.  NARROWED
MARGINAL RISK AREA ACRS IA/NEB/MO AREA WHERE THERE IS GENL MULTI
MODEL CONSENSUS ON DVLPG AXIS OF HEAVY RAINS THERE OVERNIGHT AS
COLD FRONT DROPS SWD TOWARD SRN IA AND BECOMES STATIONARY..THOUGH
THERE REMAINS FAIRLY LARGE MODEL SPREAD REGARDING POTNL AMOUNTS
THERE.  CONCERN HERE IS WITH POOLING OF PWS OF OVER 1.25 INCHES
LATER TONIGHT ALONG WITH SOME TRAINING OF CELLS ALONG E/W
FRONT..THERE COULD BE SOME ISOLD RISK OF FLASH FLOODING.   ACRS
THE TN VALLEY AND SE...EXPECT SCTD TSTMS TO SLOWLY DIMISH WITH
LOSS OF DAYTIME HEATING/INSTABILITY OVER THE NEXT SEVERAL
HOURS..THOUGH IN THE MEANTIME..ISOLD HEAVIER TSTM CELLS NEAR AND
NORTH OF STATIONARY FROM COULD LEAD TO SHORT TERM HEAVY RAINFALL
THREAT.   ACRS THE UPPER TX COAST...SURFACE DPS HAVE DROPPED
CONSIDERABLY SINCE YDA ACRS THE WRN GULF...THOUGH PWS REMAIN QUITE
HIGH ACRS THE UPR TX COAST. ADDITIONAL TSTM ACTIVITY ACRS THE
UPPER TX COAST TONIGHT IS EXPECTED TO BE RATHER ISOLD AS MID/UPR
TROF AXIS CONTINUES TO SHIFT EWD...BUT GIVEN THE HIGH PW
ENVIRONMENT...ANY CELLS THAT DO DVLP COULD BE RATHER SLOW MOVING
HEAVY RAIN PRODUCERS.  SULLIVAN


15Z UPDATE:

NOT MUCH CHANGE FROM OUR PREVIOUS OUTLOOK. JUST MADE SOME MINOR
ADJUSTMENTS TO THE EXTENT OF THE MARGINAL RISK ACROSS COASTAL
TEXAS AND OVER THE SOUTHEAST. ACROSS COASTAL TEXAS...OPTED TO
SHRINK THE MARGINAL RISK TO RIGHT ALONG THE COAST. OVERALL THE
FLASH FLOOD THREAT APPEARS TO BE DIMINISHING AS OUTFLOW HAS PUSHED
A MAJORITY OF THE INSTABILITY OFFSHORE. GETTING SOME REDEVELOPMENT
CLOSE TO THE CORE OF THE MCV...BUT IN GENERAL EXPECT THIS ACTIVITY
TO REMAIN LESS ORGANIZED AND LESS INTENSE GIVEN THE LACK OF LOW
LEVEL FLOW. WITH THE MCV NOT MOVING MUCH THROUGH THE DAY...THINK
IT MAY BE HARD TO GET ADDITIONAL ROBUST CONVECTIVE DEVELOPMENT
ONSHORE...AS THE FAVORED REGION OF ASCENT AHEAD OF THE MCV HAS
STABILIZED WITH THIS MORNINGS ACTIVITY. GIVEN ONGOING CONVECTION
NEAR THE COAST WILL CONTINUE THE MARGINAL RISK THERE FOR NOW...BUT
AS MENTIONED ABOVE...THINK WE CONTINUE TO BE ON A DOWNWARD TREND
WITH REGARDS TO THE FLASH FLOOD RISK.

ACROSS PORTIONS OF TN/GA/SC JUST MADE SOME MINOR ADJUSTMENTS TO
THE MARGINAL RISK AREA BASED ON RADAR TRENDS AND HREF V2
PROBABILITIES. STILL THINK ISOLATED 2-4" RAINFALL TOTALS WILL BE
POSSIBLE WITHIN THE MARGINAL RISK AREA WHERE CELL MERGERS OCCUR
THIS AFTERNOON.

CHENARD

PREVIOUS DISCUSSION...

MID TO UPPER TX COAST

A MARGINAL EXCESSIVE RAINFALL RISK AREA WAS MAINTAINED ALONG THE
MID TO UPPER TX COAST FOR THE UPCOMING DAY 1 PERIOD AHEAD OF SLOW
MOVING MID TO UPPER LEVEL VORTS EXPECTED TO IMPACT THE TX GULF
COAST.  CONFIDENCE ON THE EXACT HANDLING OF THESE VORTS IS LOW AS
IS THE RESULTANT CONVECTIVE EVOLUTION.  WITH PW VALUES REMAINING
ABOVE AVERAGE FROM PERSISTENT SOUTHERLY LOW LEVEL FLOW OFF THE
WESTERN GULF AND THE SLOW MOVEMENT OF THE MID TO UPPER LEVEL
VORTS---LOCALLY HEAVY TO EXCESSIVE RAINFALL AMOUNTS ARE POSSIBLE.
WHILE THE LATEST MODELS DIFFER ON MANY OF THE SHORTER TERM
DETAILS--THERE IS A CLEAR MODEL SIGNAL FOR THE HEAVY TO LOCALLY
EXCESSIVE AMOUNTS ACROSS THIS AREA.

UPPER TN VALLEY---SOUTHERN APPALACHIANS INTO PORTIONS OF THE
SOUTHEAST

A MARGINAL RISK AREA IS DEPICTED DAY 1 IN THE VICINITY OF A
SURFACE FRONTAL BOUNDARY FORECAST TO LIE FROM THE UPPER TN VALLEY
INTO THE SOUTHERN APPALACHIANS AND SOUTHEASTERN U.S.  OVERRUNNING
OF THIS BOUNDARY FROM SOUTH SOUTHWEST LOW LEVEL FLOW OVER THE TN
VALLEY AND SOUTHEASTERLY LOW LEVEL UPSLOPE FLOW INTO THE SOUTHERN
APPALACHIANS WILL SUPPORT POTENTIAL FOR WIDESPREAD MODERATE TO
HEAVY RAINS FROM CENTRAL TO EASTERN TN INTO WESTERN NC---NORTHEAST
GA AND ACROSS LARGE PORTIONS OF SC.  SLOW MOVEMENT OF CELLS WILL
POSE THE THREAT FOR ISOLATED RUNOFF ISSUES ACROSS THESE REGIONS.

SOUTHEAST NEBRASKA---SOUTHERN IA---FAR NORTHERN MO

THE TRAILING SURFACE FRONTAL BOUNDARY FROM THE LOW MOVING INTO THE
UPPER MS VALLEY/UPPER LAKES REGION WILL BECOME ORIENTED WEST TO
EAST FROM THE CENTRAL PLAINS INTO THE MID TO UPPER MS VALLEY
TUESDAY INTO TUESDAY NIGHT-EARLY WEDNESDAY.  CONVECTION SHOULD
BECOME INCREASINGLY ACTIVE ALONG THIS FRONT DURING THE SECOND HALF
OF THE DAY 1 PERIOD AS THE LOW LEVEL FLOW INTO THE BOUNDARY
STRENGTHENS.  THE GREATEST RISK OF ANY RUNOFF ISSUES APPEARS TO BE
TOWARD THE END OF THE DAY 1 PERIOD WHEN THE LOW LEVEL FLOW WILL
BECOME INCREASINGLY PARALLEL TO THE FRONTAL BOUNDARY---SUPPORTING
POTENTIAL FOR A SHORT PERIOD OF TRAINING OR BACK BUILDING OF CELLS
FROM SOUTHEAST NEBRASKA---ACROSS SOUTHERN IA AND FAR NORTHERN MO.


ORAVEC

$$





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