Mesoscale Precipitation Discussion 0154
NWS Weather Prediction Center College Park MD
1000 AM EDT Mon Apr 21 2025

Areas affected...Coastal Texas

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

Valid 211358Z - 211900Z

Summary...Showers and thunderstorms will continue through early
afternoon across the Upper and Middle Texas Coasts. Rainfall rates
in excess of 1"/hr mcould reach 3"/hr at times, leading to
rainfall of 2-3" with locally up to 5". This may cause instances
of flash flooding.

Discussion...The regional radar mosaic this morning shows a line
of showers and thunderstorms extending from near Corpus Christi,
TX northeast towards Beaumont, TX. This convection is blossoming
along a slow moving cold front analyzed by WPC which will continue
to sag very slowly southward towards the Gulf Coast through the
aftn. Rainfall rates this morning have already been estimated via
local radars of 2-3"/hr, resulting in 3-5" of rain in a few areas
in the vicinity of Houston, and these scattered intense rates are
likely to continue through the aftn.

As the front sags southward, it will encounter weak but onshore
850mb flow of 10-15 kts. While this is modest, it will be
sufficient in the presence of PWs that are 1.6 to 1.7 inches,
above the 90th percentile according to the SPC sounding
climatology, to produce intense moisture advection and convergence
into the boundary. This will combine with the approach of the LFQ
of a subtropical jet streak extending across northern Mexico to
enhance ascent, and the simulated radar from the morning CAMs
suggest storms will persist for many more hours. As instability
climbs to 2000-3000 J/kg later today, the organization of
convection may become more diffuse, but still widespread enough
that mean cloud layer winds from SW to NE will result in short
duration training. With HREF 2"/hr probabilities peaking above
40%, and the HRRR 15-min accumulated precipitation fields
indicating short-duration rain rates above 3"/hr possible, this
could cause 2-3" of rain with locally higher amounts as much as 5"
into the aftn.

Soils across the region are generally drier than normal according
to the NASA SPoRT 0-40cm soil moisture anomalies, and this is
reflected by both 1-hr and 3-hr FFG that are generally 3-4 inches.
Despite that elevated FFG, the HREF indicates a 10-30% chance of
exceedance. This suggests at least an isolated flash flood risk,
but the greatest potential will be where any slow moving storms
can train or linger across urban areas where infiltration capacity
is lower.


Weiss

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

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

LAT...LON   30839475 30829407 30359376 29789402 29449468
            28979541 28599606 28209661 27879695 27529725
            27269743 27309773 27739780 28739691 30359540