Graphic for MPD #0651

MESOSCALE PRECIPITATION DISCUSSION 0651
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1034 PM EDT MON AUG 07 2017

AREAS AFFECTED...SOUTHEAST TX

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 080234Z - 080834Z

SUMMARY...THUNDERSTORMS ARE BEGINNING TO FIRE WITHIN THE SOUTHEAST
QUADRANT OF AN MCV.  HOURLY RAIN TOTALS UP TO 2.5" AND LOCAL
AMOUNTS TO 5" ARE EXPECTED.

DISCUSSION...RADAR IMAGERY REVEALS AN MCV FROM MORNING
THUNDERSTORM ACTIVITY IN SOUTH-CENTRAL TX MOVING INTO THE REGION,
TO THE EAST-SOUTHEAST AT 10-15 KTS.  CIN HAS DEVELOPED ACROSS THE
REGION, WHICH IS ALLOWING THE INSTABILITY ALOFT/MU CAPE TO ITS
SOUTHEAST TO BE TAPPED, ON THE ORDER OF 1000-3000 J/KG.   WHILE
VAD WIND PROFILES SHOW CYCLONIC INFLOW OF 20 KTS, RADAR-BASED CELL
MOTIONS IMPLY THAT 30 KTS IS A BETTER INDICATION OF THE 850 HPA
INFLOW.  THIS IS 10 KTS ABOVE THE LEVEL OF THE MEAN 850-400 HPA
FLOW.   EFFECTIVE BULK SHEAR OF ~30 KTS EXISTS NEAR THE MCV. 
PRECIPITABLE WATER VALUES ARE 2-2.2" PER GPS DATA.

THE GUIDANCE HAS A SMALL BUT AGREEABLE MAXIMUM SCATTERED ACROSS
THE REGION OF 5", WHICH IS LIKELY DUE TO THIS MCV.  RAINFALL
EFFICIENCY IS EXPECTED TO INCREASE WITH TIME AS THE MEAN 850-400
HPA FLOW WEAKENS TO 5-10 KTS BY 09Z.  THE 18Z SSEO NEIGHBORHOOD
PROBABILITIES OF EXCEEDING THE THREE HOUR FLASH FLOOD GUIDANCE
SHOW SMALL 50%+ SPOTS BETWEEN 05 AND 09Z.  HOURLY RAIN RATES UP TO
2.5" ARE POSSIBLE NEAR ITS CENTER AND WITHIN ITS SOUTHERN AND
EASTERN QUADRANTS.  DUE TO RAINFALL OVER THE PAST 18 HOURS, FLASH
FLOOD GUIDANCE IS COMING DOWNWARD.  CONSIDERING THE AMOUNTS
EXPECTED, FLASH FLOODING IS A CONCERN, PARTICULARLY WITHIN URBAN
AREAS.

ROTH

ATTN...WFO...CRP...EWX...HGX...

ATTN...RFC...WGRFC...

LAT...LON   30689586 30209487 29509438 28279674 30039657
            30549642


Last Updated: 1034 PM EDT MON AUG 07 2017