MESOSCALE PRECIPITATION DISCUSSION 0394
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
353 PM EDT SAT JUN 24 2017

AREAS AFFECTED...SOUTHERN LA...SOUTHWEST MS...SOUTHEAST TX

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

VALID 241952Z - 242352Z

SUMMARY...SLOW MOVING SHOWERS AND THUNDERSTORMS WITH HEAVY
RAINFALL RATES ARE LIKELY TO PERSIST THROUGH THE REMAINDER OF THE
AFTERNOON HOURS.  SOME LOCALIZED FLASH FLOODING IS POSSIBLE WITH
RAINFALL RATES ON THE ORDER OF TWO INCHES PER HOUR POSSIBLE.

DISCUSSION...RECENT IR SATELLITE IMAGERY HAS INDICATED EXPANDING
DEEP CONVECTION WITH EMBEDDED OVERSHOOTING TOPS.  THE CONVECTION
IS ASSOCIATED WITH THE SLOW SOUTHWARD ADVANCE OF A COLD FRONT INTO
A VERY MOIST AND UNSTABLE AIRMASS OUT AHEAD OF IT AND IS BEING
FOCUSED NEAR A DEVELOPING WAVE OF LOW PRESSURE ALONG THE FRONT. 
MIXED LAYER CAPE ON THE ORDER OF 2000 J/KG EXISTS JUST SOUTH OF
THE ONGOING CONVECTION, AND THIS UNSTABLE INFLOW TOWARDS THE FRONT
WILL SERVE TO ENHANCE RAINFALL RATES.  THERE ARE ALSO INTERSECTING
OUTFLOW BOUNDARIES FROM EARLIER CONVECTION OVER THIS REGION.

A RIBBON OF HIGH PWS, ON THE ORDER OF 1.8 TO 2.2 INCHES PER THE
LATEST SPC MESOANALYSIS, IS POOLED ALONG AND AHEAD OF THE FRONT. 
THIS IS FACILITATING RATHER EFFICIENT RAINFALL PROCESSES FOR
HEAVIER RATES, WHICH MAY APPROACH 2 INCHES PER HOUR AT TIMES THIS
AFTERNOON.  THE LATEST HRRR EXPERIMENTAL GUIDANCE SUPPORTS SOME
IMPRESSIVELY HIGH RAINFALL TOTALS BETWEEN THE 20Z TO 00Z TIME
FRAME, WITH AMOUNTS LOCALLY UP TO 4 INCHES BY 00Z. THIS SEEMS TO
HAVE A BETTER HANDLE ON THE SITUATION THAN THE OPERATIONAL HRRR,
WHICH APPEARS TO BE UNDERDONE WITH ITS AMOUNTS. SOME FLASH
FLOODING WILL BE POSSIBLE GIVEN THESE TYPES OF RAINFALL AMOUNTS,
ESPECIALLY OVER AREAS THAT HAVE RECEIVED APPRECIABLE RAIN OVER THE
PAST FEW DAYS.

HAMRICK

ATTN...WFO...HGX...JAN...LCH...LIX...SHV...

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

LAT...LON   31779238 31699165 31399089 31169026 30718967
            29918936 29408962 29109008 29039078 29239154
            29489241 29649346 29489469 30219473 30999407
            31419356 31719309