MESOSCALE PRECIPITATION DISCUSSION 0077
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
550 AM EDT WED MAR 28 2018

AREAS AFFECTED...PORTIONS OF S-CNTRL TO E-CNTRL TX

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

VALID 280948Z - 281445Z

SUMMARY...A HEAVY RAINFALL AND FLASH FLOOD THREAT WILL EXTEND INTO
THE EARLY MORNING HOURS FOR PORTIONS OF S-CNTRL TO E-CNTRL TX.
TRAINING WITH RAIN RATES OF 1-2 IN/HR WILL BE POSSIBLE THROUGH 15Z
WITH A POSSIBLE LULL BEFORE RENEWED ACTIVITY DEVELOPS.

DISCUSSION...REGIONAL RADAR REFLECTIVITY AS OF 09Z SHOWED A BROAD
REGION OF STRATIFORM RAIN WITH EMBEDDED THUNDERSTORMS STRETCHING
FROM NERN TO CNTRL TX...ANCHORED TO THE SOUTH WITH HEAVIER
RAINFALL CORES OF 1-2 IN/HR. SOME FLASH FLOODING DUE TO REPEATING
CELLS AND TRAINING HAD BEEN OBSERVED IN THE VICINITY OF I-35 FROM
NEAR GEORGETOWN TO SAN ANTONIO...AND WWD TOWARD HONDO THROUGH 09Z.
A SUBTLE INFLECTION ON WATER VAPOR IMAGERY WOULD SUGGEST A
SHORTWAVE IS PRESENT OVER WEST TEXAS...NORTH OF THE BIG BEND...AND
INFRARED IMAGERY SHOWS NO NEW SIGNIFICANT DEVELOPMENT BETWEEN THE
ONGOING COMPLEX AND THE RIO GRANDE...PERHAPS DUE TO BRIEF
SUBSIDENCE BEHIND THE SHORTWAVE. THIS MAY ALLOW FOR A BRIEF LULL
IN ACTIVITY IN THE SHORT TERM.

HOWEVER...THE 09Z SPC MESOANALYSIS AND 1 HR FORECAST FROM THE 08Z
RAP SUPPORTED A RESERVOIR OF MLCAPE BETWEEN 500 AND 1500 J/KG FROM
I-10 BETWEEN SAN ANTONIO AND HOUSTON...DOWN TO THE SOUTH OF SAN
ANTONIO. ONGOING CONVECTION APPEARS TO BE ON THE NRN EDGE OF
AVAILABLE MLCAPE. LARGE SCALE FORCING FOR ASCENT IS STILL PRESENT
WITH THE APPROACH OF A STRONG SHORTWAVE OVER NEW MEXICO.

THEREFORE...DESPITE THE RELATIVE BREAK IN CONVECTIVE ACTIVITY TO
THE WEST OF I-35...SLY 850 MB FLOW OF 40-50 KT IS EXPECTED TO
CONTINUE THE THREAT FOR CONVECTION AND TRAINING ELEMENTS ALONG THE
SWRN FLANK OF THE ONGOING CONVECTIVE CLUSTER AS IT CONTINUES TO
TRACK OFF TOWARD THE EAST...AND 850 MB FLOW VEERS TOWARD THE
SOUTHWEST.

SOME SIGNALS FROM THE HRRR AND EXPERIMENTAL HRRR SUPPORT THIS
SCENARIO...BUT CONFIDENCE IS A BIT LIMITED WITH EVOLUTION INTO A
TYPICALLY UNFAVORABLE DIURNAL TIME OF DAY FOR FLASH FLOODING.

OTTO

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

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

LAT...LON   31309652 31199585 30749542 30119541 29469586
            29159636 28719755 28559899 29139925 29849839
            30669730