MESOSCALE PRECIPITATION DISCUSSION 0123
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
120 PM EDT SUN APR 17 2016
 
AREAS AFFECTED...PORTIONS OF CENTRAL AND EASTERN TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 171715Z - 172315Z
 
SUMMARY...SLOW-MOVING HEAVY SHOWERS AND THUNDERSTORMS ARE EXPECTED
TO CONTINUE THIS AFTERNOON WITH REPEATING CELLS AND CELL-MERGERS
LIKELY. CONCERNS FOR FLASH FLOODING WILL INCREASE THROUGH THE
AFTERNOON.

DISCUSSION...MOIST AND RELATIVELY UNSTABLE LOW LEVEL FLOW
CONTINUES TO CONVERGE NORTH ACROSS CENTRAL AND SOUTHEAST TX AND
TOWARD WHAT HAS BEEN A PERSISTENT AXIS OF HEAVY SHOWERS AND
THUNDERSTORMS. THE COLDER CONVECTIVE TOPS OVER THE LAST HOUR HAVE
BEEN GENERALLY SOUTH OF DALLAS DOWN TOWARD THE WACO AND GATESVILLE
AREA. ADDITIONAL CELLS ARE ALSO DEVELOPING JUST SOUTHEAST OF
AUSTIN WHICH IS INDICATIVE OF ADDED BOUNDARY LAYER DESTABILIZATION
WITHIN THE BROAD AND DEEPER LAYER SOUTH TO SOUTHEAST FLOW ACROSS
SOUTHEAST TX.

OVER THE NEXT FEW HOURS THERE WILL BE STRONG CONCERNS FOR SOME
VERY HEAVY RAINFALL TOTALS AS INCREASED DIABATIC HEATING/SOLAR
INSOLATION AHEAD OF THE CONVECTION HELPS DESTABILIZE THE BOUNDARY
LAYER FURTHER. THIS IS SUGGESTED IN THE LATEST VIS SATELLITE
IMAGERY WHICH SHOWS AN EXPANSIVE CU/TCU FIELD SURGING NORTH TO
NORTHWEST ACROSS SOUTH TEXAS ALONG WITH A NUMBER OF CLOUD STREETS.
THIS WILL ALLOW CONVECTION TO CONTINUE TO FOCUS ALONG A
CONVECTIVELY ENHANCED OUTFLOW BOUNDARY...AND ALSO IN A SOMEWHAT
ELEVATED FASHION OVER A WELL-DEFINED COLD POOL OVER CENTRAL TX.

THE HIRES GUIDANCE HAS BEEN TERRIBLE IN ACCURATELY DEPICTING THE
CONVECTIVE EVOLUTION TODAY ACROSS THE REGION...BUT RECENT RUNS OF
THE HRRR/HRRX ARE SUGGESTING SOME IMPRESSIVE CONVECTIVE RAINS
DEVELOPING NEAR THE CURRENT OUTFLOW BOUNDARY THROUGH THE AFTERNOON
HOURS. THE 15Z HRRR-TLE INDICATES HIGH PROBABILITIES OF OVER 6
INCHES IN 6 HOURS GENERALLY WITHIN A LINE FROM WACO TO AUSTIN TO
LLANO.

PWATS ARE GENERALLY CLOSE TO 1.5 INCHES NOW ACROSS THIS
REGION...AND WITH RATHER STRONG SBCAPE VALUES SETTING UP SOUTH F
AUSTIN...CONVECTION SHOULD TEND TO INTENSIFY WITH HEAVIER RAINFALL
RATES THROUGH THE AFTERNOON. CURRENT RADAR TRENDS INDICATE A
LIKELIHOOD OF CELL-MERGERS...AND THIS WILL ENHANCE THE RATES
FURTHER.

EXPECT RAINFALL AMOUNTS OVER THE NEXT 6 HOURS TO BE AS MUCH AS 3
TO 6 INCHES WITH LOCALLY HEAVIER AMOUNTS PERHAPS APPROACHING 8
INCHES WHERE CELL-MERGERS AND REPEATING CELLS OCCUR. THE MEAN FLOW
IS NOT VERY KEEN ON A STRONG SOUTHEAST PUSH THIS AFTERNOON...SO
EXPECT NUMEROUS REPEATING CELLS TO FOSTER HEAVY RAINFALL TOTALS
WITH AN ENHANCED FLASH FLOOD THREAT.

ORRISON

ATTN...WFO...EWX...FWD...HGX...SHV...SJT...

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

LAT...LON   33659606 33229521 31999532 30539640 29769745 
            29439866 29279981 29860028 30929971 31739906 
            32629824 33339721 33539665