MESOSCALE PRECIPITATION DISCUSSION 0649
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 AM EST TUE NOV 17 2015
 
AREAS AFFECTED...NORTHEAST TX & SOUTHEAST OK 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 170734Z - 171334Z
 
SUMMARY...THUNDERSTORMS ARE EXPECTED TO FORM NEAR DALLAS-FORT
WORTH AND MERGE WITH AN INCOMING SQUALL LINE.  HOURLY RAIN RATES
COULD REACH 2" AN HOUR, WHICH COULD LEAD TO FLASH FLOODING.

DISCUSSION...A SQUALL LINE HAS BEEN MARCHING ACROSS TX AT ~30 KTS
OVER THE PAST SEVERAL HOURS.  AHEAD OF THE SYSTEM LIES A MOISTURE
GRADIENT NEAR THE DALLAS-FORT WORTH AREA, WHERE SHOWERS HAVE BEEN
KEPT TO A MINIMUM DUE TO CAPPING ALOFT, WHICH HAS WEAKENED A BIT
BETWEEN 00Z AND 06Z PER FWD SOUNDINGS.  PRECIPITABLE WATER VALUES
OF 1.75" LIE ON THE MOIST SIDE OF THE GRADIENT, AND 850 HPA INFLOW
OF 70 KTS IS STREAMING AHEAD OF THE FRONT/SQUALL LINE.  MUCAPES OF
1000-2000 J/KG LIE ACROSS CENTRAL AND NORTH-CENTRAL TX PER RECENT
SPC MESOANALYSES.

THE CAM GUIDANCE IS NEARLY UNITED IN THE AREA OF THUNDERSTORMS
FORMING IN THE NEXT HOUR OR TWO NEAR DALLAS-FORT WORTH AS 700 HPA
TEMPERATURES DROP TOWARDS 6C, WHICH WOULD ELIMINATE THE CAP.  IT
IS POSSIBLE THAT THE RECENT SHOWER DEVELOPMENT IN SOUTHEAST OK
COULD ALSO GROW UPSCALE IN THE MEANTIME.  THESE STORMS ARE
EXPECTED TO TRAIN SLIGHTLY BEFORE MERGING IN WITH THE APPROACHING
SQUALL LINE, WHICH COULD PICK UP THE PACE TO THE EAST.  IN THIS
SORT OF DYNAMIC/FAST-MOVING CONVECTIVE ENVIRONMENT, THIS WOULD BE
THE ONLY WAY TO GET HOURLY RAIN RATES TO APPROACH 2" WHICH WOULD
THREATEN THE MODEST FLASH FLOOD GUIDANCE VALUES.  THE CAM GUIDANCE
ADVERTISES 2-4", WHICH WOULD HAVE TO FALL QUICKLY AS THE SQUALL
LINE BROADENS TEMPORARILY DUE TO THIS INTERACTION.  DUE TO THE
UNCERTAINTY, USED THE POSSIBLE CATEGORY.  

ROTH

ATTN...WFO...FWD...OUN...SHV...TSA...

ATTN...RFC...ABRFC...LMRFC...WGRFC...

LAT...LON   35009649 34869511 34509459 33679459 32779531 
            32089653 32199774 32739811 33349816 34139760