Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Sep 20 2023 06:42:15 AWUS01 KWNH 200642 FFGMPD MOZ000-ARZ000-OKZ000-KSZ000-201230- Mesoscale Precipitation Discussion 1086 NWS Weather Prediction Center College Park MD 241 AM EDT Wed Sep 20 2023 Areas affected...Portions of the Southern Plains into the Ozarks Concerning...Heavy rainfall...Flash flooding likely Valid 200640Z - 201230Z Summary...Showers and thunderstorms will continue to expand and train through the morning. Rainfall rates of 2"/hr or more are likely at times, which through training could produce 2-4" of rain with locally higher amounts. Instances of flash flooding are likely. Discussion...The regional radar mosaic tonight shows a cluster of showers and thunderstorms expanding in the vicinity of an MCV centered over far southwest MO. This MCV is lifting slowly northeast beneath a potent shortwave noted in the GOES-E WV imagery. The accompanying height falls and PVA are overlapping with the LFQ of a subtropical jet streak arcing across the Southern Plains to drive robust deep layer ascent, which is additionally aided by the isentropic upglide from a SW LLJ of 40-50 kts measured via regional VWPs lifting over a stationary boundary. This overlap of ascent is occurring into a region of robust thermodynamics characterized by PWs measured by GPS of 1.3-1.6 inches, around the 90th percentile for the date, and a strong gradient of elevated MUCAPE from 250 to 2000 J/kg, highest to the west. Within this environment, showers are increasing in coverage, with radar-estimated rainfall rates of 1.5-2"/hr producing FLASH unit-streamflow response as high as 600 cfs/smi. The high-res guidance is struggling with the current activity, so confidence in evolution is modest, and based more so on ingredients than model output. Despite that, both the HREF and RRFS TL ensembles suggest moderate probabilities reaching 30% for 2" in the next 6 hours, with the HREF forecasting even a 5-10% chance for locally 5". As the LLJ continues to surge to the NW, it will encounter a tightening pressure gradient along the isentropic surfaces, suggesting even more impressive lift through the night. This LLJ orientation will also result in strong thermodynamic advection of higher PWs and instability from the SW, which suggests convective coverage and intensity could increase into the early morning driving rainfall rates which at times will exceed 2"/hr. More concerning to the flash flood risk is that these rain rates will likely train to the SE as Corfidi vectors become increasingly right-angled to the mean 0-6km wind. While the placement of the heaviest rain axis is uncertain, it is probable that the outflow along the SW flank of this MCV will be one focus for an axis of heavy rain, with secondary maxima possible just north of the stationary front. Recent rainfall across this region has been limited, with 14-day rainfall only 25-50% of normal according to AHPS. This has resulted in low 40cm soil moisture and 3-hr FFG that has recovered to generally 3"/3hrs. Although the HREF exceedance probabilities are modest, likely both due to these dry soils and a lack of high-res consensus, the setup suggests that training of these rain rates will result in at least isolated instances of flash flooding overnight and into the early morning. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-J3FzANjVJ8JxdZ3QX9y5142LfEVDqcP8eH57UuFf3shNcJNwZy1pHcrtNML2McqAEHf= FiUv9MgEBJEE3MPaGBPXHmo$ for graphic product... ATTN...WFO...EAX...ICT...LZK...OUN...SGF...TOP...TSA... ATTN...RFC...ABRFC...LMRFC...MBRFC...NWC... LAT...LON 38329470 38149291 37579236 36999218 35979264=20 35379330 34989448 35119571 35649671 36089736=20 36429769 36999777 37479726 37869619=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) .