Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat May 06 2023 19:58:39 FOUS30 KWBC 061958 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 357 PM EDT Sat May 06 2023 Day 1 Valid 16Z Sat May 06 2023 - 12Z Sun May 07 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE LOWER MISSISSIPPI VALLEY INTO THE SOUTHERN PLAINS AND THE MID-MISSISSIPPI VALLEY INTO THE OHIO VALLEY... ....Mid-Mississippi Valley into the Ohio Valley... There will be a resurgence of moisture and the low-level jet later this evening and into the overnight hours as the warm front moves into the region. There is some ongoing convection this morning, however there will likely be additional development near the edge of the instability axis that will have the potential to produce moderate to heavy rainfall- particularly from northeast Missouri to parts of Indiana. There is also a signal for a strong cell/cluster of cells to quickly dive southeast into Kentucky and Tennessee that could produce up to 2.5-3 inches/hr along its track. While portions of the this region have been somewhat drier of late, given the environment, isolated instances of flash flooding may arise. Therefore a Marginal Risk was hoisted for this period. Campbell ....Southern Plains and Lower Mississippi Valley... 16Z update... The latest guidance is showing a stronger, more organized line of convection lifting north and east across eastern Texas into Oklahoma with multiple hours of rainfall rates pf 1 to 2+ inches/hr. The speed and duration suggested that the Marginal Risk previous over northeast Texas needed to be expanded much further into southeast Oklahoma and western Arkansas. Some of the guidance is also signaling backbuilding of storms across southern Louisiana/Texas border, therefore the Marginal over the Mississippi Delta region was also broadened as well to reflect this trend. Campbell Maintained the Marginal Risk area for excessive rainfall over portions of the Lower Mississippi Valley as well as portions of Texas. A quasi-stationary boundary will remain parked in the same areas...leading to another round of convection in many of the same places where thunderstorms occurred on Thursday night/Friday morning and again in the early-morning hours of today. There is a possibility that storms will traverse flood sensitive portions of LA and MS...including Baton Rouge, New Orleans, and Biloxi...as the move towards the southeast. The expectation is that some convection will be lingering at the start of the Day 1 period but taper off...followed by additional convection later in the afternoon and evening. This will keep the soils in the area primed for additional flash flooding. In Texas...the focus for convection will be just a hair farther north as compared to today. Given the antecedent conditions..the Marginal Risk area there still looks warranted. Bann Day 2 Valid 12Z Sun May 07 2023 - 12Z Mon May 08 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE MIDWEST... 21Z update... Consensus of 1 to 3 inches across this part of the country persists from the previous run and WPC forecast, although very isolated areas of 4 to 6 inches can not be ruled out. The latest guidance continued with the small westward shift especially across portions of the Iowa and Missouri -the Marginal Risk area was nudged westward by 1-2 counties on the northwest side. There also continues to be some uncertainty on where the heaviest QPF will fall near the southern bounds, however consensus suggests centering over Kentucky. Only minor reshaping of the Marginal Risk to reflect the trends were made at this time. Campbell Even though there has been some convergence of ideas among the models, the forecast remains below average in confidence in placement of the heavier rainfall amounts/rates and any associated risk of excessive rainfall across the Midwest on Sunday. The trend noted on Friday afternoon of a subtle northward shift in the guidance has continued in the 06/00Z forecast cycle...although the better focus this run has been more northwest than northeast for the larger magnitude of instability and surface low pressure development with a warm front towards the east being the focus for more widespread rainfall.=20 As a result...the inherited Marginal Risk area was nudged westward...although lower FFGs on the eastern periphery of the Marginal Risk area meant smaller adjustments there. A steady southwesterly flow adding atmospheric moisture to the area behind the warm front will help boost MUCAPE values approach 2,000 J/kg Sunday afternoon and evening, so any storms that fire will have a favorable environment to work with. How the different streams interact with each other and the timing of weak shortwave energy that can help trigger and focus convection remains far from clear, Expect continued adjustments with future updates as the details become more clear. Bann Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6MuBibtIT3owvo6kSUpErmJ189hr7sc-pQNBrBsTRhX5= sYyT5TGP1W0aazLIrLhOXsoUFBvcIwS-vpOz7CXq_E9Cwbw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6MuBibtIT3owvo6kSUpErmJ189hr7sc-pQNBrBsTRhX5= sYyT5TGP1W0aazLIrLhOXsoUFBvcIwS-vpOz7CXqt-bZk_0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6MuBibtIT3owvo6kSUpErmJ189hr7sc-pQNBrBsTRhX5= sYyT5TGP1W0aazLIrLhOXsoUFBvcIwS-vpOz7CXqLYbFYOM$=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) .