EXCESSIVE RAINFALL DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
300 PM EDT THU APR 21 2011
 
...VALID 18Z THU APR 21 2011 - 00Z SAT APR 23 2011...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...
 

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E COU 20 NNW ALN 25 SSW TAZ 20 NW SLO ENL 15 NW HSB
30 ENE M30 15 ESE CKV BNA 20 S MQY 20 NNW MDQ 30 NNW MSL
15 WSW MKL 10 ENE JBR 15 NE BVX 30 SSE FLP 35 SSW FLP 25 SW HRO
15 S TQH 10 SSW GMJ 30 ENE JLN 50 S SZL 25 SE DMO 30 E COU.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ESE MLU MLU 30 SSE ELD 15 S ELD 15 WNW ELD 20 NW ELD
25 SE M89 30 ESE M89 20 S PBF 15 W GLH 40 NNE TVR 25 NNE TVR
10 ENE TVR 10 WSW TVR 30 WSW TVR 20 ESE MLU.

 

SERN AR/NERN LA...

THIS INITIAL AREA OF ORGANIZED CONVECTION ALONG AND NORTH OF THE
FRONTAL BNDRY OVR THE LOWER MS VALLEY REGION HAS BECOME VERY
PROGRESSIVE TO THE SOUTHEAST INTO MS THIS AFTERNOON. 
HOWEVER...ADDITIONAL CONVECTION CONT TO FORM UPSTREAM ALONG THIS
BNDRY AND MAY PUSH SEWD OVR AREAS THAT HAVE RECEIVED HVY PCPN
EARLIER.  MODEL PERFORMANCE WITH THIS CONVECTION HAS NOT BEEN VERY
GOOD..LEADING TO LOW CONFIDENCE AS TO HOW LONG ADDITIONAL
CONVECTION MAY CONT TO FIRE AND PUSH SEWD ALONG THIS BNDRY. 
LATEST NAM AND GFS CONT TO SHOW SOME SHRTWV ENERGY MOVG EWD IN THE
0000-0600 UTC TIME FRAME FROM ERN TX INTO NRN LA.  THIS MAY
SUPPORT ADDITIONAL ACTIVITY THRU THIS TIME BEFORE THE PRIMARY
FOCUS WL BE FARTHER NWD.  IN AREAS OF TRAINING OR WHERE PRIOR
CONVECTION HAS OCCURRED...ISOLATED RUNOFF ISSUES ARE POSSIBLE FROM
ISOLATED 1"+ AMTS IN A BRIEF PERIOD.

MID MS VALLEY...LOWER OH VALLEY..LOWER TN VALLEY...

THE EMPHASIS FOR ADDITIONAL ORGANIZED CONVECTION WL LIKELY BE
SHIFTING NWD LATE THIS AFTERNOON INTO THE OVERNIGHT PERIOD FROM
FAR NRN AR..EWD INTO THE MID MS VALLEY...LOWER OH VALLEY...UPR TN
VALLEY. OVERALL THERE IS LOW CONFIDENCE THIS PERIOD WITH THE
INCREASINGLY WET PATTERN DEVELOPING ACRS THESE AREAS.   WHILE
MODELS HAVE GENERAL EVOLUTION TO THE LARGE SCALE FLOW WITH AN
AMPLIFYING TROF MOVG OUT OF THE NWRN U.S/GTBASIN AND INTO THE NRN
TO CNTRL PLAINS...THEY DO DIFFER WITH THEIR RESPECTIVE QPF AXES
ALONG THE NEWD LIFTING WARM FRONT FROM THE LOWER MS VALLEY INTO
THE OH VALLEY.  THE HI RES ARW WAS FOLLOWED MORE CLOSELY THIS
PERIOD FOR  THE QPF AXES AS IT WAS FARTHER TO THE SOUTH WITH THIS
AXIS THAN THE OTHER OPERATIONAL GUIDANCE...ESPECIALLY WITH THE
FIRST ROUND OF CONVECTION EXPECTED TO SPREAD EWD FROM ERN OK AND
AR TONIGHT INTO FRI.  THIS WL BE FOLLOWED BY ANOTHER ROUND OF
ORGANIZED CONVECTION THAT MAY FORM FARTHER TO THE NORTH FRI OVR MO
AND SPREAD EWD INTO THE LOWER TO MID OH RIVER VALLEY.  WITH BOTH
OF THESE ROUNDS OF CONVECTION...MDT TO HVY TOTALS ARE
POSSIBLE..WITH AREAL AVG .50-1"+ AMTS DEPICTED FROM THE MID MS
VALLEY EWD INTO THE LOWER TO MID OH RIVER VALLEY...LOWER TN VALLEY
AND CUMBERLAND VALLEY AREA...WITH ISOLATED SHRT TERM TOTALS OF
1-2"+ POSSIBLE.  THIS MAY PRODUCE ISOLATED RUNOFF ISSUES ACRS
THESE AREAS.ORAVEC

$$