MESOSCALE PRECIPITATION DISCUSSION 0613
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
414 AM EDT WED AUG 02 2017

AREAS AFFECTED...NORTHEAST TX & NORTHWEST LA

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

VALID 020812Z - 021412Z

SUMMARY...SHOWERS WITH SLOWLY COOLING CLOUD TOPS ARE DEVELOPING
WITHIN A SATURATED ENVIRONMENT.  HOURLY RAIN RATES UP TO 2.5",
WITH LOCAL AMOUNTS TO 4", ARE EXPECTED.

DISCUSSION...RECENT SPC MESOANALYSES INDICATE A RECENT UPTICK IN
MUCAPE VALUES AHEAD OF AN INCOMING SHORTWAVE ACROSS OK, SHOWING A
BROADER AREA OF 500-1000 J/KG NORTH OF A ZONE OF WIND SHEAR WHICH
RECENTLY RETURNED FROM THE GULF OF MEXICO WITH SLIGHTLY WARMER AIR
TO ITS SOUTH.  SHOWERS APPEAR TO BE CONCENTRATED TO THE NORTH AND
NORTHEAST OF A DEW POINT GRADIENT IN THE WARM SECTOR NEAR THE 98TH
MERIDIAN.  EFFECTIVE BULK SHEAR OF 20 KTS EXISTS IN THIS REGION. 
PRECIPITABLE WATER VALUES OF 2-2.3" LIE IN THE AREA PER GPS
VALUES, WHICH COULD MEAN A HIGHER WET BULB ZERO THAN SEEN ON THE
00Z SOUNDINGS (15,000 FEET).  THE ATMOSPHERE APPEARS SATURATED
BOTH ON SATELLITE IMAGERY AND IN THE 00Z SOUNDINGS FROM SHREVEPORT
LA AND DALLAS TX, WHICH IS MAKING EFFECTIVE USE OF THE LIMITED
INSTABILITY.

SHOWERS AND THUNDERSTORMS SHOULD INCREASE IN COVERAGE ELEVATED
OVER THE SURFACE BOUNDARY UP TOWARDS THE RED RIVER OF THE SOUTH,
EXTENDING TOWARDS THE 850 HPA REFLECTION OF THE BOUNDARY.  WITH
THE BULK SHEAR NEARLY DOUBLE THE VALUE OF THE 850-400 HPA WIND,
AND SURFACE FLOW OPPOSING THE FLOW ALOFT, SLOW SHOWER AND
THUNDERSTORM MOTION TO THE EAST AT ~10 KTS IS EXPECTED.  THE
MESOSCALE GUIDANCE, BOTH AT 12Z AND 00Z, SHOWED SPLOTCHY AREAS OF
4"+ IN THIS AREA.  WITH INSTABILITY FORECAST TO RISE FURTHER, RAIN
RATES SHOULD FOLLOW SUIT.  THE NEIGHBORHOOD PROBABILITIES OF
EXCEEDING THE THREE HOUR FLASH FLOOD GUIDANCE VALUES PEAK IN THE
11-14Z PERIOD WITHIN THE 30-50% RANGE -- HIGH ENOUGH TO BE OF
CONCERN.  HOURLY RAIN RATES UP TO 2.5", AND LOCAL AMOUNTS OF 4",
ARE EXPECTED, WHICH WOULD BE MOST PROBLEMATIC IN URBAN AREAS.

ROTH

ATTN...WFO...FWD...HGX...LCH...SHV...

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

LAT...LON   33699734 33569443 32929286 31479232 31389496
            32019772 32829858