Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Oct 24 2024 15:28:13 FOUS30 KWBC 241527 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1127 AM 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=20 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=20 where urban conditions further increase potential for limited=20 infiltration and high run-off capable of localized flooding.=20 Gallina Introduced a Marginal Risk for portions of the Middle MS Valley,=20 from northwest IL and southeast IA into northern MO (and adjacent=20 portions of far northeast KS). Strengthening southwesterly low-=20 level flow (850 mb) to 40-50 kts this evening will usher in PWATs=20 to near 1.25" (well above the 90th percentile, per SPC sounding=20 climatology), along with sufficient instability (ML CAPE 1000+=20 J/kg) and forcing (potent shortwave trough crossing the Central=20 Plains) for convective development. Strong vertical shear (~50 kts) with idealized curving hodographs will likely favor discrete=20 convection (with both the mean flow and bunkers right vectors=20 favoring storm motions of 20-30 kts), and despite relatively low=20 PWs (particularly compared to warm season convection) any=20 supercells will likely be capable of 1-2"/hr rainfall rates (per=20 40-km neighborhood HREF probabilities for 1"/1-hr exceedance of=20 40-50%). While 1-2" totals should be well tolerated by soils (and=20 largely beneficial, given dry antecedent conditions), localized=20 training could result in too much rainfall (2"+) too quickly (in a=20 matter of 2-3 hours). Given this threat, an isolated instance or=20 two of flash flooding is possible. Churchill Day 2 Valid 12Z Fri Oct 25 2024 - 12Z Sat Oct 26 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill Day 3 Valid 12Z Sat Oct 26 2024 - 12Z Sun Oct 27 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-woBPXJejXzOj-4XwX8D8hM215shrYAIwGKmzOXAAqzS= M_4BDh1GDt5X66_FfgRBwaLHCkwqzzcKYNAWWCdfwGzuUoA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-woBPXJejXzOj-4XwX8D8hM215shrYAIwGKmzOXAAqzS= M_4BDh1GDt5X66_FfgRBwaLHCkwqzzcKYNAWWCdfBV0UbvM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-woBPXJejXzOj-4XwX8D8hM215shrYAIwGKmzOXAAqzS= M_4BDh1GDt5X66_FfgRBwaLHCkwqzzcKYNAWWCdf_RdJ274$=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) .