Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Apr 04 2023 08:08:21 FOUS30 KWBC 040808 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 407 AM EDT Tue Apr 04 2023 Day 1 Valid 12Z Tue Apr 04 2023 - 12Z Wed Apr 05 2023 ....THERE ARE MARGINAL RISKS FOR EXCESSIVE RAINFALL FOR PORTIONS OF SOUTH-CENTRAL U.S. AND GREAT LAKES REGION... ....Western Great Lakes... A powerful cyclone over the Midwest will be responsible for two particular areas where Excessive Rainfall is possible today. Focusing first in the western Great Lakes, the primary surface low is set to track from the Central Plains Tuesday morning and into the Upper Midwest by Tuesday evening. The warm front associated with the low pressure will also push north, tracking through the Middle MS River Valley Tuesday midday and reach the the Great Lakes by Tuesday evening. Between the exceptionally deep upper trough in the West and strong ridging in the Southeast, the integrated vapor transport will steadily increase from South Texas to the Upper Midwest. By 00Z Wednesday, NAEFS shows IVT values will be >750 kg/m/s and above the 99th climatological percentile from southeast TX to northern IL. PWs in the Marginal Risk area will eventually reach 1.10-1.20", which is above the 90th climatological percentile according to NAEFS. The excellent moisture transport and rising PWs does provide enough moisture for developing thunderstorms to tap into, leading to locally heavy rainfall rates. Most guidance is in agreement in MUCAPE >1,000 J/kg, which is high enough to support heavy rainfall rates. The biggest limiting factors in the flash flood threat are storm motions and drier air at upper levels. Area averaged soundings show that the 700-300mb layer is quite dry, and the elevated convection will also contain some modest hail CAPE as well. Mean 850-300mb winds are will be at a progressive 50-60 knots as well so barring the potential for training convection, which is not as likely as convection much farther south, residence time of heavy rainfall rates will be on the shorter side. The wild card in this setup are soil temps, which are still quite chilly. In addition, western MI has also received as much as 300% of rainfall over the past 7 days. FFGs are also as low as 1"/hr in parts of eastern WI, northern IL, western IA, and western MI. With the available instability and anomalous moisture, the Marginal Risk still looks to be in good shape at this time given the fast storm motions will help to keep the flash flood threat much more localized. ....East TX/OK, Arkansas, and Middle MS River Valley... Unlike their neighbors to the north, the atmosphere will be more unstable and feature less intrusion of the dryslot from the powerful cyclone in parts of the South Central U.S. Storm motions will still be rather fast, but this region has the right entrance region of a 150 knot 250mb jet streak positioned overhead, maximizing vertical ascent atop the atmosphere. Over 1,000 J/kg of MLCAPE and PWs approaching 1.5" will coincide within an atmospheric profile Tuesday evening that features 80-90% RH values in the 1000-500mb layer. Unlike the soundings to the north, the atmospheric column will feature deeper warm cloud layers and more saturated profiles, allowing these developing thunderstorms Tuesday night to be more efficient rainfall producers. The slower progression of the cold front and strengthening LLJ after 00Z Wed will prompt thunderstorms to blossom in these areas along a pre-frontal trough initially, followed by the cold front sweeping through these areas early Wednesday morning. It is along the pre-frontal trough with mean winds in the LCL-LFC cloud layer running parallel to it where there is the potential for training convection. However, storm motions will likely be as fast as 40-50 knots, so residency time of hourly rainfall rates up to 2"/hr would be shorter and keep the best flash flood potential to only segments of training storms. East TX may be the most prone location for possible flash flooding given recent 7-day rainfall totals have surpassed 300% of normal. However, the lower 1-hr FFGs are in the Ozarks and into the Middle MS Valley where some values are as low as 1.5"/hr. Given the quick progression of the anticipated convection, have maintained the Marginal Risk but will mention a Slight Risk upgrade may be required should hi-res CAMs begin showing higher QPF totals in future forecast cycles. Mullinax 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!-ANzIQshLAyS-gB8SpR-iAxbyjvi0KwnY2y32rdAY1HT= bzYUmVHWMnCp3JNOZLriH3r7cYtyk6ywGfKnd0uYB6PsO_w$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-ANzIQshLAyS-gB8SpR-iAxbyjvi0KwnY2y32rdAY1HT= bzYUmVHWMnCp3JNOZLriH3r7cYtyk6ywGfKnd0uYQ4CCYaw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-ANzIQshLAyS-gB8SpR-iAxbyjvi0KwnY2y32rdAY1HT= bzYUmVHWMnCp3JNOZLriH3r7cYtyk6ywGfKnd0uYnLFyJUw$=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) .