Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Mar 23 2023 19:50:08 FOUS30 KWBC 231950 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 349 PM EDT Thu Mar 23 2023 Day 1 Valid 16Z Thu Mar 23 2023 - 12Z Fri Mar 24 2023 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL OVER A PORTION OF THE MID/SOUTHERN MISSISSIPPI VALLEY.. An abundant Gulf moisture will be streaming northward ahead of a deep-layer trough that ejects from the Southern Rockies and results in strengthening low level flow. At about the same time, upper level divergence from an upper level jet aids in surface low pressure forming along a quasi-stationary front extending from Oklahoma northeastward into the Ohio/Tennessee Valley. A quick look at the 12Z NAM and the latest runs of the HRRR still fundamentally show precipitation breaking out along the same axis as earlier runs although the timing of heavy rainfall may be just a tad quicker to develop than shown in the past couple of runs.=20 12Z soundings showed an axis of stronger flow (30+ kts) from the Gulf coast region towards the ArkLaTex. Models still point to the axis of an anticyclonic upper jet approaching the region that increases upper level divergence by late afternoon and early evening...so the potential for 1 to 2 inch/hour rain rates still looks to be on-track. While this area is not as saturated as it was a couple of weeks ago...there is local concern given that ground conditions are still fairly moist. Overall...there were a few minor adjustments to the on-going outlook areas based on the latest guidance but those changes do not reflect a major shift in forecast reasoning. Bann Day 2 Valid 12Z Fri Mar 24 2023 - 12Z Sat Mar 25 2023 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL FROM THE OZARKS TO THE OHIO VALLEY... Showers and thunderstorms will be on-going at the start of the forecast period in proximity to the sprawling frontal boundary with moisture flux convergence increasing across parts of the Mississippi Valley and into the Ohio Valley as a surface low pressure with trailing cold front moves east across the Southern Plains. By 25/00Z a PW fetch of 1.5 inches will span from the Gulf Coast to the MO boot heel, feeding right into the frontal boundary, which is some (+2 to +2.5 standard deviations greater than climatology for late March. It is expected that multiple storms will track across areas soaked from recent rains and will likely surpass local FFGs early into the Day 2 period. The latest model runs have been persistent with areal averages of 2 to 4+ inches amounts. There is always a concern that convection will build a bit farther south towards the instability than suggested by the models...but confidence remains above normal in this cycle given run to run consistency in both placement and rainfall amounts. The Marginal Risk area was trimmed once again just a bit across the Lower Mississippi Valley. Bann Day 3 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 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!54RdV_xSyES2bybffiuwJCUlDp4BUBlku_UC9WGsYuPV= sJ6144u2Ti__oR0v1kLg59cgK-W2Gid1iNskqvr1h5DBzW4$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!54RdV_xSyES2bybffiuwJCUlDp4BUBlku_UC9WGsYuPV= sJ6144u2Ti__oR0v1kLg59cgK-W2Gid1iNskqvr1FgL8PHE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!54RdV_xSyES2bybffiuwJCUlDp4BUBlku_UC9WGsYuPV= sJ6144u2Ti__oR0v1kLg59cgK-W2Gid1iNskqvr1uRjYo8s$=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) .