Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Oct 24 2024 20:14:19 FOUS30 KWBC 242014 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 414 PM EDT Thu Oct 24 2024 Day 1 Valid 16Z Thu Oct 24 2024 - 12Z Fri Oct 25 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY... ....16z update... Very little change in initial reasoning. 12z forecast guidance continues to denote a bimodal distribution of potential heavy rainfall corridors across central IA into northern IL and/or across northeast MO also toward northern IL with a quicker/eastward shift of the intense rainfall rates capable to exceed short-term FFG values. This includes an expansion into the Chicagoland region where urban conditions further increase potential for limited infiltration and high run-off capable of localized flooding. Gallina Introduced a Marginal Risk for portions of the Middle MS Valley, from northwest IL and southeast IA into northern MO (and adjacent portions of far northeast KS). Strengthening southwesterly low- level flow (850 mb) to 40-50 kts this evening will usher in PWATs to near 1.25" (well above the 90th percentile, per SPC sounding climatology), along with sufficient instability (ML CAPE 1000+ J/kg) and forcing (potent shortwave trough crossing the Central Plains) for convective development. Strong vertical shear (~50 kts) with idealized curving hodographs will likely favor discrete convection (with both the mean flow and bunkers right vectors favoring storm motions of 20-30 kts), and despite relatively low PWs (particularly compared to warm season convection) any supercells will likely be capable of 1-2"/hr rainfall rates (per 40-km neighborhood HREF probabilities for 1"/1-hr exceedance of 40-50%). While 1-2" totals should be well tolerated by soils (and largely beneficial, given dry antecedent conditions), localized training could result in too much rainfall (2"+) too quickly (in a matter of 2-3 hours). Given this threat, an isolated instance or two of flash flooding is possible. Churchill Day 2 Valid 12Z Fri Oct 25 2024 - 12Z Sat Oct 26 2024 ....2000 UTC Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 3 Valid 12Z Sat Oct 26 2024 - 12Z Sun Oct 27 2024 ....2000 UTC Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7PTQWnpA2dSpwG0_v9eCcUWF1s_a8lDgJa1ivq1gAFZN= HvDidgbb_SYOTRkZ_7n28wlxHEBQXl636-RdnsRXHZTQJ8E$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7PTQWnpA2dSpwG0_v9eCcUWF1s_a8lDgJa1ivq1gAFZN= HvDidgbb_SYOTRkZ_7n28wlxHEBQXl636-RdnsRXxdBnVjY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7PTQWnpA2dSpwG0_v9eCcUWF1s_a8lDgJa1ivq1gAFZN= HvDidgbb_SYOTRkZ_7n28wlxHEBQXl636-RdnsRXqORX1oE$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .