Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Sep 27 2023 01:19:28 AWUS01 KWNH 270119 FFGMPD WIZ000-ILZ000-MNZ000-IAZ000-270600- Mesoscale Precipitation Discussion 1105 NWS Weather Prediction Center College Park MD 918 PM EDT Tue Sep 26 2023 Areas affected...Portions of the Upper Midwest Concerning...Heavy rainfall...Flash flooding possible Valid 270117Z - 270600Z Summary...Slow moving showers and thunderstorms rotating around a stacked low pressure will continue tonight. Rainfall rates at times will exceed 1"/hr, which through storm motions could produce rainfall as high as 2-3" in a few locations. This could result in isolated instances of flash flooding. Discussion...The GOES-E WV imagery clearly indicates a potent closed low spinning slowly over eastern IA. Downstream of this feature to the east, modest mid-level divergence is combining with the slow height falls to drive ascent, resulting in repeated developing of showers and thunderstorms into MO/IL/IN. Additional ascent is occurring within the weak LFQ of a jet streak rounding the base of this trough, with low-level convergence along a stationary front also aiding. This deep layer lift is occurring into favorable thermodynamics characterized by PWs of 1.2-1.3 inches, and a plume of 1000-1500 J/kg SBCAPE which is still not yet overturned according to the SPC RAP mesoanalysis. Convection in this region has been generally scattered, but radar estimated rain rates have reached 1.5"/hr at times. As the stacked low pivots slowly eastward tonight, ascent will persist, acting upon elevated MUCAPE that will remain around 1000 J/kg. This should drive the development of rounds of thunderstorms, primarily south and east of the low center, which will then rotate NW within deep layer cyclonic flow. Mean 0-6km winds will remain light around the upper low, 5-15 kts, with similarly collapsed and aligned Corfidi vectors indicating a likelihood for training of cells. Additionally, some backbuilding of convection is possible towards the SE and into the modest 850mb inflow. This is conducive to training of these already slow moving storms, which will likely result in extended temporal duration of heavy rain rates. The HREF and HRRR sub-hourly graphics indicate rainfall rates will reach 1-2"/hr at times, which through this motion could produce 2-3" of rainfall in a few areas as reflected by HREF probabilities as high as 40% for 3"/6hrs. Rainfall across this region has been well above normal the last 14-day as reflected by AHPS departures reaching 300% of normal. This has resulted in compromised FFG as low as 1.5"/3hrs. However, overall recent dryness has keep 40cm soil moisture percentiles still below normal, which will somewhat inhibit the flash flood risk. Still, training of these impressive rain rates, especially if they occur atop areas that have received heavy rain recently, or in any urban areas, could produce isolated instances of flash flooding tonight. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4BuPQgDGxrU_u1ZdB_X9pdwoQm4ZwPRlGkSo06wp7XiL68ciZ0cG6K2wVvp6KBtCD_E2= wNKli_TMbe1I_-jcgQBHbnE$ for graphic product... ATTN...WFO...ARX...DVN...ILX...LOT...MKX... ATTN...RFC...NCRFC...OHRFC...NWC... LAT...LON 43709079 43338916 42958834 42428779 41748753=20 40848766 40228813 39968905 40028999 40279065=20 40799046 41329070 41889117 42579156 43369161=20 43559144=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) .