Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 24 2024 07:08:52 AWUS01 KWNH 240708 FFGMPD LAZ000-TXZ000-241230- Mesoscale Precipitation Discussion 0715 NWS Weather Prediction Center College Park MD 308 AM EDT Wed Jul 24 2024 Areas affected...Middle Texas Coast through Southwest Louisiana Concerning...Heavy rainfall...Flash flooding likely Valid 240707Z - 241230Z Summary...Showers and thunderstorms blossoming over the Northwest Gulf of Mexico will spread onshore through the morning. Backbuilding of 2-4"/hr rates will result in 3-5" of rain with locally higher amounts. Flash flooding is likely. Discussion...The GOES-E WV imagery early this morning clearly portrays the extreme environment setting up across the Texas and Louisiana coasts this morning. An upper low is positioned over Tamaulipas, Mexico, while a secondary vorticity impulse spins across the NW Gulf of Mexico (GoM). This is helping to advect copious low-level moisture, noted via the SFC-850mb ALPW, northward into the western Gulf Coast. At the same time, a stream of high level moisture emerging from the eastern Pacific is traversing northeast in the 500-300mb ALPW fields to intersect this same region. This is manifesting as deeply saturated 00Z U/A soundings at KCRP and KLCH with measured PWs of 2.35 and 2.27 inches, respectively, nearing the daily record at both sites. This is combining with slowly increasing MLCAPE of 1000 J/kg (more than 2000 J/kg over the source region in the GoM) to yield extremely favorable thermodynamics for heavy rainfall. Into these thermodynamics, ascent is slowly increasing through the approach of the broad mid-level trough axis to the NW, a surface trough approaching from the GoM, weak mid-level impulses shedding through the flow, and strengthening frictional/moisture convergence. The regional radar mosaic shows a few convective cells beginning to propagate onshore as even more widespread activity blossoms over the GoM. Regional VWPs indicate that 850mb inflow out of the S/SW has increased to 15-20 kts, drawing the more robust thermodynamics northward, and as this persists thunderstorm development onshore should rapidly increase. This is progged by nearly all of the recent high-res CAMs simulated reflectivity, leading to higher confidence in the evolution the next few hours. As thunderstorms expand and intensify, rainfall rates will almost certainly (>70% chance on the HREF and REFS) exceed 2"/hr, and at times may reach 4"/hr as shown by HRRR 15-min accumulations of 1". Most concerning about these rain rates is that the Corfidi vectors will become increasingly aligned anti-parallel to the mean 0-6km wind and collapse to just 5 kts, suggesting storms will backbuild into the higher instability over the GoM and may exhibit near-zero net motion at times along the frictional convergence boundary. Where this occurs, rainfall of 3-5" is likely, and the HREF has a 40-60% chance for more than 5 inches from Galveston Bay to Lake Charles, LA. This area is also favored for the heaviest rain by the REFS PMM of more than 5 inches, and the experimental OU-CAPS SAM which aligns closely with the HREF EAS probabilities, further increasing the confidence that this will be the hardest hit region through the morning. Farther southwest, training of cells could still produce 2-3" of rain with locally higher amounts as far as Oso Bay, but confidence is somewhat less as to whether the heaviest rain will stay offshore in this area of the Middle Texas Coast. 14-day rainfall across the Gulf Coast has generally been above normal, although a subtle axis of below normal rain does exist along the Upper TX Coast into LA. However, recent rainfall has saturated the the top soils as noted by NASA SPoRT 0-10cm RSM that is 70-90% across the entire area. Regardless of soil conditions, slow movement and repeating rounds of these intense rain rates will likely cause flash flooding across much of the region this morning. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7ZIo7tgK6mkZLua1FK-pAv29wfcj6iGEv9ldJ_qvTJXye5prHzLD7pHit028SMXCWBJu= dcG_mBKjgBjxMPiVA_LgCf0$ for graphic product... ATTN...WFO...CRP...HGX...LCH... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 30559378 30549312 30349272 29989258 29729273=20 29659315 29419384 29359428 29169462 28899513=20 28659565 28439617 28149664 27849693 27579715=20 27409739 27499756 27759765 28209726 28789667=20 29249599 29789545 30229506 30519436=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) .