Mesoscale Precipitation Discussion 0151
NWS Weather Prediction Center College Park MD
708 PM EDT Sun Apr 20 2025

Areas affected...middle/upper TX Coastal Plain

Concerning...Heavy rainfall...Flash flooding possible

Valid 202306Z - 210435Z

SUMMARY...Isolated flash flooding will be possible from training,
slow movement and/or backbuilding thunderstorms along portions of
the TX Coastal Plain through early tonight. Rainfall rates could
exceed 2 to 3 in/hr resulting in storm total rainfall of 3 to 6
inches.

DISCUSSION...Visible satellite and radar imagery showed a line of
scattered thunderstorms extending from eastern TX to the middle TX
coast, located along a trough axis positioned ahead of a cold
front/dryline which extended SSW from northeast TX into the
southern Coastal Plain. The environment was supportive of heavy
rain with PWATs of 1.7-1.9 inches, MLCAPE of 2000-2500 J/kg and
effective bulk shear of 25-40 kt (22Z SPC mesoanalysis).

Over the past few hours, cell motions have been averaging 20-25 kt
toward the NE (similar to the 0-6 km AGL mean wind), parallel to
the initiating trough axis, although slower motions were observed
south of 29 degrees N, where shear values were weaker. Cells to
the south were less numerous but have had a history of
backbuilding and rainfall rates of ~1 inch in 15 minutes across
portions of eastern Victoria County.

MLCAPE of at least 1000-2000 J/kg with little to no CIN is
forecast by the RAP to persist across the TX Coastal Plain beyond
sunset along with some degree of continued convection. While bulk
shear values are forecast to lower from south to north with a
departing mid-level shortwave over KS/MO, there may remain a
narrow zone where sufficient shear exists for at least
quasi-organized cells where low level inflow remains modest along
the middle to upper TX coast after 00Z. The combination of slowing
cell motions with a continued (though modest) influx of low level
moisture may be enough to sustain a cell or two with slow net
movement (backbuilding/training) which could result in localized
heavy rain with 3 to 6 inches possible.

However, this threat is considered to be very isolated in nature
and given dry antecedent conditions from a lack of rainfall over
the past two weeks, any impactful threat of heavy rainfall would
likely remain isolated and urban in nature.

Otto

ATTN...WFO...CRP...EWX...HGX...LCH...SHV...

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

LAT...LON   31499497 31249426 29809509 28639650 28679709
            29419670 30369581