MESOSCALE PRECIPITATION DISCUSSION 0391
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
705 AM EDT FRI SEP 19 2014
 
AREAS AFFECTED...SOUTHEAST TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 191104Z - 191604Z
 
SUMMARY...THUNDERSTORMS WITH HEAVY RAINFALL HAVE DEVELOPED ACROSS
THE REGION SINCE 08Z.  CONSIDERING THE AVAILABLE MOISTURE, HOURLY
RAIN RATES UP TO 2.5" ARE POSSIBLE WHICH COULD LEAD TO FLASH
FLOODING.

DISCUSSION...ELEVATED THUNDERSTORM ACTIVITY HAS FORMED OVER A
STATIONARY FRONT DURING THE PAST FEW HOURS JUST INLAND OF THE TX
COAST, NEAR A ZONE OF WEAK SURFACE CONVERGENCE ACROSS INTERIOR
SOUTHEAST TX.  ITS DEVELOPMENT IS BEING AIDED BY A JET STREAK
ALOFT AND CAPE VALUES (MIXED AND UNSTABLE) OF 1000-2000 J/KG LIE
NEAR AND SOUTHEAST OF THE BOUNDARY PER THE MOST RECENT SPC
MESOANALYSIS.  LOW-LEVEL INFLOW AND 0-6 KM BULK SHEAR IS MINIMAL,
WHICH SHOULD KEEP CONVECTION OF A SINGLE CELL OR PULSE NATURE. 
PRECIPITABLE WATER VALUES OVER 2", AROUND THE 90TH PERCENTILE FOR
MID-SEPTEMBER, SUPPORT HOURLY RAIN RATES OF 2.5" WITHIN THIS
ACTIVITY.

MESOSCALE QPF GUIDANCE INDICATES THAT LOCAL AMOUNTS OF 2-4" ARE
POSSIBLE IN THIS REGION, WHICH WOULD LIKELY BE THE RESULT OF CELL
MERGERS.  AS CAPE/INSTABILITY BECOMES EXHAUSTED IN THE COLD SECTOR
OF THE BOUNDARY RELATIVELY EASILY, THE THREAT SHOULD BECOME
INCREASINGLY COASTAL WITH TIME.  THE 00Z SSEO NEIGHBORHOOD
PROBABILITIES OF EXCEEDING THREE HOURLY FLASH FLOOD GUIDANCE
SUGGEST THAT THE THREAT OF EXCEEDING FLASH FLOOD GUIDANCE IN THE
REGION COULD PERSIST AT LONG AS 19Z ALONG PORTIONS OF THE MIDDLE
AND UPPER TX COAST.  SINCE CONVECTION IS OF THE PULSE VARIETY,
BELIEVE THE THREAT COULD BE OF SHORTER DURATION, SO USED A FIVE
HOUR WINDOW FOR THIS MPD.  THE REGION HAS BEEN SATURATED BY
RAINFALL OVER THE PAST COUPLE DAYS, MAKING IT MORE SUSCEPTIBLE TO
FLASH FLOODING.  FLASH FLOODING IS CONSIDERED POSSIBLE HERE.

ROTH

ATTN...WFO...CRP...EWX...FWD...HGX...LCH...

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

LAT...LON   30949579 30009392 29729381 29649384 29569419 
            29179498 28429616 28509658 29139748 30229792 
            30869765