MESOSCALE PRECIPITATION DISCUSSION 0003
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1202 PM EST THU JAN 22 2015
 
AREAS AFFECTED...COASTAL SOUTHEAST TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 221701Z - 222101Z
 
SUMMARY...A LENGTHENING BAND OF CONVECTION IS DEVELOPING ALONG THE
MIDDLE AND UPPER TX COAST.  WITH RAIN RATES UP TO 1.75" AN HOUR
EXPECTED, FLASH FLOODING IS CONSIDERED POSSIBLE.

DISCUSSION...SURFACE-BASED CONVECTION IS FORMING NEAR A SURFACE
LOW MOVING UP THE TX COAST AND EXTENDING NORTHEASTWARD NEAR A
COASTAL FRONT. RECENT SATELLITE IMAGERY SHOWS CLOUD TOPS ARE
COOLING.  CAPE VALUES OF 500-1000 J/KG LURK JUST OFFSHORE THE
MIDDLE TX COAST, WHICH APPEARS TO BE AIDING THE DEVELOPING
THUNDERSTORM BAND.  PRECIPITABLE WATER VALUES ARE JUST ABOVE 1.50"
PER RECENT RAP RUNS, NEAR THE 99TH PERCENTILE FOR LATE JANUARY. 
INFLOW AT 850 HPA PER AREA VAD WIND PROFILES IS 30-40 KNOTS, NEAR
THE MAGNITUDE OF THE 850-400 MEAN WIND, WHICH IS HELPING TO
ORGANIZE THE THUNDERSTORM BAND.

PRECIPITABLE WATER VALUES THIS HIGH SUPPORT HOURLY RAIN RATES UP
TO 1.75" AN HOUR -- RADAR ESTIMATES SO FAR ARE UP TO 1.5" PER
HOUR.  THE EXPECTATION OVER THE NEXT FEW HOURS IS FOR THE BAND TO
MOVE NORTHEAST FARTHER UP THE TEXAS COAST.  THE LIMITING FACTOR
WITHIN THE SHORT TERM APPEARS TO BE DECREASING CAPE AND 850 HPA
INFLOW MAINLY AFTER 19Z PER RECENT RAP RUNS -- ALLOWED THE MPD TO
EXTEND TO 21Z IN CASE THIS PROCESS TAKES LONGER THAN EXPECTED. 
THE MESOSCALE GUIDANCE IS GROWING MORE BULLISH AND CONVERGING UPON
HEAVY PRECIPITATION IN THIS AREA, WITH THE GUIDANCE GENERALLY
SHOWING 3-4" IN A SHORT PERIOD OF TIME.  FLASH FLOODING IS
POSSIBLE IN THIS AREA, PARTICULARLY OVER URBAN AREAS NEAR HOUSTON
AND GALVESTON.

ROTH

ATTN...WFO...CRP...HGX...LCH...

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

LAT...LON   30349371 29739358 28839556 28339662 28929693 
            29789584