Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 19 2023 12:04:43 AWUS01 KWNH 191204 FFGMPD TNZ000-KYZ000-INZ000-ILZ000-MOZ000-191800- Mesoscale Precipitation Discussion 0762 NWS Weather Prediction Center College Park MD 804 AM EDT Wed Jul 19 2023 Areas affected...eastern MO, southern IL, western KY, western TN Concerning...Heavy rainfall...Flash flooding likely Valid 191203Z - 191800Z Summary...Thunderstorms developing along a NW to SE oriented convergence axis will persist through the morning. These thunderstorms will have rain rates of 1-3"/hr at times, which through training could produce locally more than 5" of rain. This will occur on top of saturated soils. Flash flooding is likely, some of which could be significant and life-threatening. Discussion...The regional radar mosaic this morning shows a continuation of an impressive NW to SE oriented MCS developing along a low-level convergent axis from eastern Missouri through central Tennessee. Convection has been ongoing all night along this boundary, and is likely to continue for several more hours as the 850mb LLJ of 30-40 kts noted on regional VWPs, more than +4 standard deviations according to the SREF, continues to lift into the area. A stationary front analyzed by WPC just south of the convection is serving as another lifting mechanism as the LLJ rises impressively and isentropically atop this boundary and then collides into the convergence axis to the northeast. MUCAPE according to the SPC RAP analysis remains 2000-3000 J/kg, with PWs measured by GPS as high as 1.9-2.0 inches, around the 90th percentile for the date. These extreme thermodynamics will continue to surge into the area on this LLJ, maintaining an environment favorable for 1-3"/hr rainfall rates. The high-res guidance still features some differences in where the heaviest rain axis will setup this morning, but recent runs of the HRRR, ARW, and CONEST are all initializing well enough to be helpful. It is likely that convection will continue to develop and train SE on 10-15 kts Corfidi vectors, with backbuilding occurring into the greater instability to the west as the LLJ begins to gradually veer. Impressive thickness diffluence positioned over western KY and into TN should also support continued intensity of these thunderstorms. What is concerning is that despite the thickness lines suggesting this complex will try to dive southeast with time, that will be offset both by weaker instability east and the veering of the LLJ, indicating the overall footprint of the heaviest rainfall will likely be narrow along the greatest moisture transport vector convergence, and across similar areas already impacted overnight. 12-hr rainfall from MRMS and mesonet observations has already been 2-5" with locally higher amounts, and the HREF exceedance probabilities for 3" and 5" reach 40% and 25%, respectively, atop these same areas. The heavy rain overnight is already leading all-time high USGS streamflows and flash flooding. With soils already saturated, any additional rain will lead to rapid runoff and flash flooding. Should the axis of heavy rain focus atop the same areas, this could result in locally catastrophic and life-threatening flash flooding, with maximum rainfall possibly reaching 8-10" for the entire event. Even in areas that haven't received as much rainfall overnight, the training of 1-3"/hr rain rates could produce 1-3+" of rain leading to other instances of flash flooding through the late morning. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-sC7toCPQe6YbuB_pjDk98nDdYI0uoA7IhA3GXmQ-MMMxYsDcH1xQbsV4R75f8TXQVvi= KEPTiT6-FzXqT4rXZlg8NQY$ for graphic product... ATTN...WFO...HUN...LMK...LSX...MEG...OHX...PAH...SGF... ATTN...RFC...LMRFC...MBRFC...NCRFC...OHRFC...NWC... LAT...LON 38619199 38599061 38248906 37708756 36838592=20 36278548 35758570 35438603 35228690 35458772=20 35728810 36268884 36718968 37289079 37609155=20 37879227 38059263 38419269=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) .