Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 02 2023 08:19:13 FOUS30 KWBC 020819 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 418 AM EDT Wed Aug 02 2023 Day 1 Valid 12Z Wed Aug 02 2023 - 12Z Thu Aug 03 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID MISSISSIPPI VALLEY... ....Mid Mississippi to Lower Ohio Valleys... A significant flash flooding event is expected across portions of Mid Mississippi Valley this morning and then again late tonight into Thursday morning, impacting much of north-central to east-central Missouri with a narrow but potentialy extreme amount of rainfall in short period of time. This includes the greater St. Louis metro area, particularly for tonight/early Thursday morning. Early this morning, convection has continued to blossom and expand in coverage from southern Iowa through central Missouri at the nose of the strengthening low level jet. The latest RAP analysis showed upwards of 40 kts overrunning a frontal boundary draped across the region. This coincides with favorable forcing for ascent from shortwave energy rounding the periphery of the strong upper ridge axis. Finally, moisture anomalies are quite high this morning, where the blended TPW product shows values exceeding 2", and likely to increase further. The current convection will slowly drift south/southeast through central/east-central Missouri through mid to late morning. High warm cloud depths and an axis of 2000-2500 J/kg MUCAPE this morning will support higher end rain rates exceeding 2-3"/hr (localized 3"+ hourly totals possible) and with backbuilding/training convection, several hours of these intense rain rates in a narrow/localized swath is likely to produce a swath of extreme rainfall totaling 4-8"+ (localized 8-10") through the morning, which is supported by the 00Z HREF showing 50-60 percent probabilties for 5"+. This activity will begin to wane after 15Z (most intense rain rates through 15Z) but may not completely subside until early afternoon. Then later tonight into Thursday morning, another round of locally significant heavy rainfall is expected to develop across eastern Missouri into southern Illinois. Continued anomalous moisture, another surging low level jet, favorable instability, and high warm cloud depths all point toward intense rain rates (2-3"/hr) and localized higher end rain totals. The axis of heaviest rain may fall just east/southeast of this morning's heavy rainfall footprint, but very close overlap and also in and around the St. Louis metro. The 00Z HREF probs for 5"+ again reach 50-60 percent for tonight/early Thursday morning, maximized just west of St. Louis which shows even a near 20 percent chance for 8" totals. The 00Z CAMs generally all point to an higher end Moderate Risk flash flood event event and with the proximity to the STL metro, higher end flash flooding will be possible due to the intensity of rainfall for several hours over a more urbanzed location. ....Great Basin to North/Central Rockies and High Plains... Widespread showers and thunderstorms are expected Wednesday into Wednesday night aided by shortwave energy and right entrance dynamics with a strengthening jet streak over the northern Rockies. Moisture will be very anomalous, upwards of 1-1.25" of precipitable water and nearly 3 standard deviations above normal, based on the latest model guidance and with the daytime heating and terrain influences, localized intense rain rates between 0.5-1"/hr will be possible. The 00Z guidance continues to highlight portions of eastern Idaho, western Wyoming, and northern Utah with the greater probabilities of seeing the higher rainfall totals (localized 1-2") as well as portions of far northern Colorado and southeast Wyoming where Slight Risks were maintained from the previous forecast cycle. Taylor Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8WD9Yn5wWUFmWhbrhVtyrJULGDoIT9oXuCf5CJ9Yz5gx= rPy0z73LQzGGR6IXxGJguZLfFzVgRNgerMlFhO0MLd1wwLU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8WD9Yn5wWUFmWhbrhVtyrJULGDoIT9oXuCf5CJ9Yz5gx= rPy0z73LQzGGR6IXxGJguZLfFzVgRNgerMlFhO0MX2NToKc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8WD9Yn5wWUFmWhbrhVtyrJULGDoIT9oXuCf5CJ9Yz5gx= rPy0z73LQzGGR6IXxGJguZLfFzVgRNgerMlFhO0MEup864g$=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) .