Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 25 2023 00:22:02 FOUS30 KWBC 250021 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 821 PM EDT Fri Mar 24 2023 Day 1 Valid 01Z Sat Mar 25 2023 - 12Z Sat Mar 25 2023 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL FROM THE EASTERN ARKANSAS TO THE LOWER OHIO VALLEY... An impressive/strong shortwave trough was noted in the latest water vapor imagery this evening across portions of the ArkLaTex while at the surface low pressure and its associated cold front continues to track eastward through Arkansas. Regional radar shows organizing clusters of strong to severe thunderstorms along/ahead of the front from eastern Arkansas through western Mississippi. A stationary boundary remains draped near/south of the Ohio Valley where a large shield of stratiform precipitation is training over parts of southeast Missouri into southern Illinois. In the warm sector, the line of the intense thunderstorms is expected to continue racing eastward through portions of western/middle Tennessee into northern Mississippi. A surging low-level jet characterized by 850 mb flow of 50-60 kts will bring both anomalous moisture northward (upwards of 2" PWs) and an axis of higher instability (1000-2000 J/kg MUCAPE) up through portions of middle TN. With the mean flow offset the storm motions, the line should begin to race further ahead, particularly after 04Z when the low level setup becomes less conducive for intense rain rates. Until then, merging line clusters and some favorable setup for repeating rounds combined with the greater instability and high moisture should yield rain rates up to 2" in a hour at times. More impressively is the 5-minute rain rates that could exceed 0.5" at times in the stronger embedded cores (as shown by the experimental WoFS). This could yield a quick 1-2" that would result in flash flooding. Further north, the setup favors more moderate rainfall but over a longer period thanks to the flow being more parallel to the storm motions. From southeast Missouri through parts of western/central Kentucky and southern Indiana, a stripe of 2-3" of rainfall this evening is expected based on the 18Z HREF probabilities and latest runs of the HRRR. So although rain rates may not be as impressive (perhaps up to 1" hourly totals), the longer duration is expected to be the main driver for initiating flooding. For this update, the risk areas were adjusted based on the latest radar trends (trimming back edge some) with just some minor tweaks to the eastern edges based on the most recent guidance. MPD #125 issued at 2350Z covers part of the warm sector flash flood potential, valid through 0450Z while MPD #124 discusses flash flood potential further north into MO/IL. Taylor Day 2 Valid 12Z Sat Mar 25 2023 - 12Z Sun Mar 26 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 3 Valid 12Z Sun Mar 26 2023 - 12Z Mon Mar 27 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST... There is a Marginal Risk of excessive rainfall across portions of the Southeast U.S. as moisture starts getting drawn north from the Gulf of Mexico and encounters a quasi-stationary front that sets up across the region. In response to the increasing moisture, the atmosphere should become increasingly unstable with upwards of 1000 J per kg of MUCAPE. At the same time, Corfidi vectors support at least some training. However...the lack of any upper level support should keep any convection that fires along the front rather disorganized/scattered and high flash flood guidance values should work to limit the flash flooding potential. As a result...made few changes to the on-going Marginal Risk area. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_lyLCIx5y4akHG0YADlkiD0SnVCdLJZ6kYSTkh7BbfuJ= Fw_laqlcnnH6Zm3o5unjh8KKKuM9Xs_Kah6ijfMv_fy8ZxQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_lyLCIx5y4akHG0YADlkiD0SnVCdLJZ6kYSTkh7BbfuJ= Fw_laqlcnnH6Zm3o5unjh8KKKuM9Xs_Kah6ijfMvA8iWoKQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_lyLCIx5y4akHG0YADlkiD0SnVCdLJZ6kYSTkh7BbfuJ= Fw_laqlcnnH6Zm3o5unjh8KKKuM9Xs_Kah6ijfMvRLB2uLQ$=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) .