Subj : HVYRAIN: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Nov 14 2022 19:50:16 FOUS30 KWBC 141950 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 249 PM EST Mon Nov 14 2022 Day 1 Valid 16Z Mon Nov 14 2022 - 12Z Tue Nov 15 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS THE UPPER TEXAS COAST AND CENTRAL GULF COAST... 16z update: No sizable changes were required with the update based on the new 12z guidance including the 12z HREF probability information. The trend toward best convergence off-shore continues, but there is some hint of increased spacing from the near surface based cells and the elevated development that the Upper Texas Coast still indicate a solid probability for excessive rainfall rates both in the hourly and sub-hourly time frame to maintain the Marginal Risk of Excessive Rainfall. Toward late evening/overnight hours as the progressive cells track east across S LA, the best mid to upper level forcing lifts northward and decouples sufficiently from the elevated unstable air to produce the most intense rates. Still, a low-end Marginal Risk remains along/south of I-10 resulting in limited changes to the risk area, carving back a bit in coastal MS/AL. Gallina A vigorous upper level trough tracking into the Southern Plains on Monday will spawn low pressure over central and South Texas. A frontal boundary along the Texas coast will act as the focus for developing shower and thunderstorm activity over southeast Texas around midday. Farther east, there is a strong dome of high pressure entrenched across much of the eastern third of the CONUS. The resulting pressure gradient between the low pressure center in Texas and high pressure in the East will foster a strong southerly 850mb jet in the western Gulf of Mexico. 850mb winds over the northwestern Gulf of Mexico between 18-00Z will be in the 40-50 knot range, which is around the 90th climatological percentile. IVT values for 00Z Tuesday just southeast of Lake Charles are also >750 kg/m/s, which is above the 97.5 climatological percentile as well. In terms of moisture, PWs will be >1.5" along the southeast Texas coast and as far east as the central Gulf Coast, which by Monday evening PWs may top 1.75". Lastly, regarding instability, the best MLCAPE will generally reside along the coastline with CAMs suggesting values anywhere from as little as 250 J/kg to 1,000 J/kg. This combined with the moisture levels and triggers in place should result in strong thunderstorms that produce rainfall rates >2"/hr in some cases. The latest 00Z HREF does show 2"/hr rainfall probabilities as high as 40-50% along some portions of the Louisiana coast. Despite the favorable parameters for heavy rainfall, storm motions will be quite progressive. Expected 850-300mb mean winds will be 40-50 knots and FFGs remain relatively high. The 00Z HREF does show 10-20% probabilities for 3-hr QPF > 3-hr FFGs from the southeast Texas coast to far southern Louisiana. These probabilities and the locally heavy rainfall rates support maintaining the Marginal Risk with the more urbanized communities and poor drainage areas most prone to potential flash flooding. Outside of that, the fast storm motions and higher FFGs throughout the at-risk region should keep any flash flood threat to being very localized. Mullinax Day 2 Valid 12Z Tue Nov 15 2022 - 12Z Wed Nov 16 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Gallina Day 3 Valid 12Z Wed Nov 16 2022 - 12Z Thu Nov 17 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Gallina =20 Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!54If6GVudIAg-XGSqMTs-usEfUaKCJOVXuI-WKg-mgV5= 5Hf3USNyySwa2UjDaBko8KNs9vBmo_CVgluow3fn2Ji4u2o$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!54If6GVudIAg-XGSqMTs-usEfUaKCJOVXuI-WKg-mgV5= 5Hf3USNyySwa2UjDaBko8KNs9vBmo_CVgluow3fnsOE8HJc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!54If6GVudIAg-XGSqMTs-usEfUaKCJOVXuI-WKg-mgV5= 5Hf3USNyySwa2UjDaBko8KNs9vBmo_CVgluow3fnePKrMdY$=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) .