AWUS01 KWNH 201525

FFGMPD

TXZ000-202130-



Mesoscale Precipitation Discussion 0480

NWS Weather Prediction Center College Park MD

1124 AM EDT Sat Jun 20 2026



Areas affected...South Texas and the Texas Coast



Concerning...Heavy rainfall...Flash flooding likely



Valid 201530Z - 202130Z



Summary...Convection will rapidly expand across South Texas and

the Texas Coast this afternoon. Rainfall rates of 2-3"/hr are

expected, which through slow storm motions could produce 3-5" of

rainfall. Flash flooding is likely.



Discussion...An upper low spinning over parts of South Texas is

clearly evident this morning as a spin in visible satellite

imagery. A few clusters of thunderstorms with heavy rainfall have

been ongoing already this morning just inland from the Middle

Texas Coast, but additional convection is beginning to expand as

noted via improving glaciation in the GOES-E experimental

day-cloud phase RGB.



Thermodynamics across the area are impressive. PWs as measured via

GPS are above 2.3" inches, or near the daily record according to

the SPC sounding climatology. These tropical PWs are combining

with MLCAPE above 2500 J/kg to support the increasing thunderstorm

coverage, with ascent driven both by the upper low and attendant

mid-level trough axis, as well as a developing bay-breeze which

will produce low-level convergence. Additionally, 850mb inflow of

10-20 kts is roughly equal to the mean wind, but locally some

enhancement is occurring immediately downstream of the upper low,

forcing more intense thermodynamic advection into the Texas Coast.



During the next few hours, the environment will support an

expansion and intensification of thunderstorms, especially along

the bay breeze and immediately downstream of the upper low. This

is reflected by available high-res guidance simulated

reflectivity, and confidence is increasing in widespread coverage

by this aftn. Any thunderstorms will contain extremely heavy rain

rates (already measured by MRMS at 1.75"/hr), with both HREF and

REFS 1-hr rainfall probabilities reaching 30-50% for 2"/hr.



These rain rates themselves could cause instances of flash

flooding since soils are primed (0-40cm soul moisture above the

95th percentile) with FFG around 3"/3hrs. However, Corfidi vectors

become aligned more obliquely right of the mean flow, which is

itself parallel to the developing boundary and only around 10 kts.

This suggests a high potential for regenerating and training of

cells, leading to rainfall that may (40-50% chance) exceed 3", and

could (20% chance) top 5" in some locations, leading to at least

scattered instances of flash flooding.



Weiss



...Please see www.wpc.ncep.noaa.gov for graphic product...



ATTN...WFO...BRO...CRP...EWX...HGX...



ATTN...RFC...FWR...NWC...



LAT...LON   29939610 29829557 29679525 29389507 28929496 

            28389511 27979552 27709619 27299660 26969678 

            26639706 26329725 26079750 26039795 26219851 

            26409886 26679918 26909947 27099964 27439967 

            27779951 27889917 27969883 28119837 28399811 

            28689799 29409732 29809667