Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 09 2025 18:22:47 AWUS01 KWNH 091822 FFGMPD LAZ000-TXZ000-100000- Mesoscale Precipitation Discussion 0628 NWS Weather Prediction Center College Park MD 221 PM EDT Wed Jul 09 2025 Areas affected...Middle and Upper Texas Coast into Southwest Louisiana Concerning...Heavy rainfall...Flash flooding possible Valid 091819Z - 100000Z Summary...Showers and thunderstorms will increase in coverage along the Middle and Upper Texas Coasts through the afternoon. Rainfall rates will intensify to 2-4"/hr, resulting in pockets of 2-3" of rain with locally higher amounts. Flash flooding is possible. Discussion...The regional radar mosaic this afternoon shows rapidly expanding coverage of showers and thunderstorms across the Middle and Upper Texas coasts, with activity lifting slowly northward across the coastal plain. This activity is responding to extreme thermodynamics, as PWs sampled via GPS are 2.0-2.1 inches, which is around the 90th percentile for the area according to the SPC sounding climatology, paired with MLCAPE that is over 2000 J/kg. Into these robust thermodynamics, forcing for ascent continues to maximize in response to a shortwave and accompanying strung out vorticity maxima drifting southward from North Texas, and impressive upper level divergence as the region is sandwiched between mid-level synoptic high pressure ridges. Additionally, light onshore low level flow is allowing the gulf breeze to push inland, functioning as an axis for convergence and storm development. The overlap of this ascent and moisture is driving rain rates which have been estimated via KHGX WSR-88D to be 1.5"/hr, leading to MRMS measured rainfall above 1.5" in a few spots the past hour. The high-res CAMs are in general under-representing the current activity, although the ARW/ARW2 seem to have the best handle on the current situation. Despite that, all CAMs indicate rapid expansion of coverage during the next few hours, which indicates that showers and thunderstorms should become numerous to widespread, which is additionally supported by the favorable overlap of instability, moisture, and ascent. As storms become more numerous, mergers and collisions will become more likely as bulk shear remains minimal, with resulting interactions leading to rapid updraft development. In the anomalous environment, rainfall rates of more than 2"/hr are expected as forecast by HREF (REFS) neighborhood probabilities reaching 30% (50%), with brief rainfall rates of 4"/hr possible as reflected by HRRR 15-min rainfall peaking around 1". Mean 0-6km winds will remain light at just 5 kts, which when combined with the pulse type storms indicates slow and chaotic motions that could result in 2-3" of rain with local amounts as much as 5" into the evening. 0-40cm soil moisture from NASA SPoRT is saturated above the 95th percentile in many areas, resulting in FFG that is compromised, especially for this region, to as low as 2.5"/3hrs, and both the HREF and REFS probabilities indicate a medium change (30-60%) of exceedance. This suggests that despite a lack of organization, these intense rainfall rates, especially during slow and chaotic motions or across more urban areas, could create rapid runoff leading to instances of flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8yy2sDn2ran2vWR6TZzzlIezAchrqa8YRkbVAi7Wifad3oi7-EcpvwM-R9lCu8xVVoyD= POhcj_ZdT_yE9IMZz4_vdGI$ for graphic product... ATTN...WFO...CRP...EWX...FWD...HGX...LCH...SHV... ATTN...RFC...FWR...ORN...NWC... LAT...LON 31539407 31349344 31029288 30779260 30479259=20 30109274 29649358 29209446 29029476 28759525=20 28389597 27859698 27779765 27979806 28249830=20 28859819 29649771 30219709 31149578 31449491=20 =20=20=20=20=20=20=20=20=20=20=20=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .