Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Dec 24 2023 03:16:32 AWUS01 KWNH 240315 FFGMPD TXZ000-240910- Mesoscale Precipitation Discussion 1217 NWS Weather Prediction Center College Park MD 1014 PM EST Sat Dec 23 2023 Areas affected...middle/upper TX coast Concerning...Heavy rainfall...Flash flooding possible Valid 240311Z - 240910Z SUMMARY...The threat for flash flooding is expected to steadily increase overnight along the middle and upper TX coastline. Areas of training with rainfall rates of 1 to 2+ in/hr are expected along with 6-hr totals of 3-4 inches on a localized basis. DISCUSSION...Regional radar imagery at 0230Z showed widespread light to moderate rain along the TX Coastal Plain with embedded areas of heavy rain near Matagorda Bay and just east of Galveston Bay. The rain was due to a combination of warm advection and lift out ahead of a southern stream shortwave near South TX. Moisture return was ongoing into TX from the Gulf of Mexico with precipitable water values of 1.5 to 1.7 inches from the TX coast to locations as far inland as Waco and San Antonio (RAOBs and GPS data). Over the Gulf, an axis of low level convergence was estimated to extend southeastward from Galveston Bay into the west-central Gulf of Mexico (via surface observations and RAP analysis data through 850 mb). Meanwhile, MLCAPE was variable across the region, with as little as 100 J/kg along the upper TX coast to over 500 J/kg inland from the middle TX coast via the 02Z SPC mesoanalysis page (MUCAPE values slightly higher). Forcing for ascent is likely to increase over the next 6 hours as the shortwave near South TX continues to advance ENE and as coupled jet exit/entrance regions focus increasing divergence aloft over southeastern TX. In the lower levels, directional wind and speed shear will focus areas of convergence near the middle/upper TX coast, most likely between Matagorda and Galveston Bay via the latest RAP forecast. Mean steering flow from the SSW could allow for areas of training/repeating of stronger cells containing high rainfall rates. Peak rainfall rates are expected to average 1-2 in/hr, but locally higher rates cannot be ruled out. CAPE will be a limiting factor for higher rates with the latest RAP guidance suggesting better forcing along the upper TX coast but better instability setting up farther south in the vicinity of Matagorda Bay and offshore...25-50 miles south...of Galveston Bay. Given relatively high flash flood guidance values, areas of flash flooding that develop should remain localized. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-W8uZxroshA1PBBoSGSGZmsEoGB9VK49LZLRC76ky6Mj7aq3cCyRGeTDlxFY1ab_dQgZ= A6-NBQ9tFkC9hTbpD5OFKKo$ for graphic product... ATTN...WFO...CRP...EWX...HGX...LCH... ATTN...RFC...WGRFC...NWC... LAT...LON 30939474 30309403 29539409 28599521 27929651=20 27929700 28329735 29029740 30079693 30789624=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .