Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 240013
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
813 PM EDT SUN APR 23 2017

...VALID 01Z MON APR 24 2017 - 12Z MON APR 24 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SW AKQ 15 WSW GSB ILM 15 SSE SUT 10 SSE CRE 45 SSW MYR
30 SSE CHS 35 E HXD LHW 10 SE DQH 10 W VLD 10 NNE MGR 20 ESE WRB
AHN 1A5 35 ENE TYS 30 ESE 1A6 30 NW 6V3 10 NW BKW 25 NNW HSP OFP
15 SW AKQ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NW NBC TBR 15 E DBN 20 SSW HQU 15 WNW 27A 15 W CEU 25 NE 1A5
20 W TRI 15 SSW I16 15 SE LWB 20 N LYH 25 SSE FVX HNZ 10 SE IGX
POB 15 SSW CPC 40 SSW MYR 20 SSW CHS 20 NW NBC.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SW DAN 15 N EXX 10 NE FQD 30 NNE AVL TRI 10 ENE 6V3 10 N PSK
25 SE ROA 10 SW DAN.


...01 UTC UPDATE...

DISCONTINUED THREAT AREAS FOR SOUTH FL AS CONVECTION HAS MOVED
MAINLY OFFSHORE. ALSO TRIMMED THE WRN PERIPHERY OF THE PREVIOUSLY
ISSUED MARGINAL AND SLIGHT THREAT AREAS FOR THE SERN US CONSISTENT
WITH SYSTEM TRANSLATION AND RECENT SATELLITE/RADAR GUIDANCE
TRENDS. WPC DID THOUGH JUST ISSUE NEW MESOSCALE DISCUSSION #139
FOR THE ONGOING LEAD HEAVY RAINFALL EPISODE.

SCHICHTEL


...SOUTHERN-CENTRAL APPALACHIANS / SOUTHEASTERN U.S. / MID
ATLANTIC...

NO MAJOR CHANGES MADE TO THE ON-GOING EXCESSIVE RAINFALL OUTLOOK
ACROSS THIS PART OF THE COUNTRY.  RAINFALL RATES THROUGH THE
MORNING HAVE BEEN FAIRLY MODEST...WITH BETTER COVERAGE STAYING OUT
WEST SO FAR.  12Z UPPER AIR SHOWED ONLY MODEST
INSTABILITY...GENERALLY LIGHT FLOW AND PRECIPITABLE WATER VALUES
RUNNING RIGHT AROUND AN INCH.  THAT HAS HELD PRECIPITATION RATES
TO THE ORDER OF HALF INCH PER 6 HOURS ACROSS THE TN VALLEY AND
LESS ALONG THE APPALACHIANS AND IN THE CAROLINAS.

THE DECISION TO KEEP THE MODERATE IN PLACE WAS BASED ON THE
CHANGES IN THE LARGER SCALE FLOW PATTERN SHOWN BY THE MODELS FOR
LATER TODAY AND TONIGHT.  WHAT STARTS OUT AS A POSITIVELY TILTED
UPPER LEVEL TROUGH WILL DEEPEN AS IT PIVOTS TO THE SOUTHEAST WITH
A CLOSED MID LEVEL LOW EVENTUALLY TRAVERSING THE SOUTHEASTERN
STATES.  THIS PIVOTING WILL RESULT IN INCREASINGLY DIFLUENT
MID/UPPER LEVEL FLOW AND ASSOCIATED DIVERGENCE TO THE
EAST/NORTHEAST OF THE LOW.  IN ADDITION...A DUAL UPPER LEVEL JET
STRUCTURE WILL GRADUALLY GET INTO A POSITION TO ENHANCE UPPER
LEVEL DIVERGENCE OVER THE WESTERN CAROLINAS LATER THIS EVENING.

THIS SHOULD LEAD TO AN INCREASE IN AREAL COVERAGE AND RAINFALL
INTENSITY IN THE AREA OF MODERATE RISK LATER TONIGHT.  WHILE
ACKNOWLEDGING THAT...THE MODELS NEVER GENERATE A GREAT DEAL OF
INSTABILITY THIS FAR NORTH WHICH RESULTS IN ONLY WEAK TO MODERATE
UPDRAFT STRENGTH IN A REGION THAT MORE OR LESS HAS MOIST ADIABATIC
LAPSE RATES ALOFT. WHILE THIS WOULD CAP THE SHORT TERM RAINFALL
RATES AT LEAST TO SOME DEGREE...THE STRENGTHENING DYNAMICAL
PROFILE WITH A MATURING WCB/BAROCLINIC LEAF AND STRENGTHENING
LOW-MID LEVEL MOISTURE FLUX WILL SOMEWHAT COMPENSATE...ESPECIALLY
OVER THE HIGHER TERRAIN GIVEN THE UPSLOPE ENHANCEMENT. INDEED THE
ENSEMBLE PRECIPITABLE WATER PROGS INCREASE ANOMALIES TO BETWEEN 2
TO 2.5 STANDARD DEVIATIONS ABOVE CLIMATOLOGY AND INCREASING
MAGNITUDE OF MOISTURE TRANSPORT/FLUX.  AS A RESULT WE SUSPECT
CONDITIONS WILL BECOME BETTER FOR EXCESSIVE RAINFALL HERE GIVEN
THE INCREASING DYNAMICAL SUPPORT...POTENTIAL FOR CELL TRAINING AND
POSSIBLE INTERACTION WITH THE TERRAIN.

TO THE SOUTH OF THAT AREA...SAW LITTLE REASON TO MAKE ANY
ADJUSTMENTS TO THE SLIGHT RISK ACROSS PARTS OF GA...SOUTH CAROLINA
OR SOUTHERN NORTH CAROLINA.  THE INSTABILITY WILL BE STRONGER THAN
AREAS UP TO THE NORTH AND WEST WHICH SHOULD SUPPORT HIGHER
RAINFALL RATES.  DESPITE THE HIGHER RATES...STILL THINK A SLIGHT
RISK OF EXCESSIVE RAINFALL IS IN ORDER GIVEN HIGHER FLASH FLOOD
GUIDANCE VALUES AND THE CONVECTIVE MODE.

BANN
$$




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