Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Apr 24 2025 15:51:50 FOUS30 KWBC 241551 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1151 AM EDT Thu Apr 24 2025 Day 1 Valid 12Z Thu Apr 24 2025 - 12Z Fri Apr 25 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR EASTERN LOUISIANA, NORTHEAST TEXAS, AND NORTHEASTERN KANSAS THROUGH CENTRAL=20 IOWA... ....16Z Update... The inherited Slight Risk across much of the Plains was divided into two much smaller risk areas with this update, with the middle carved out back down to a Marginal. The CAMs guidance has been in poor agreement regarding how these MCSs, as well as any new convection later this afternoon, will behave through tonight. Where there is at least some consensus among the guidance is for greater amounts of convection in the new, smaller Slight Risk areas and less in the middle, which was the catalyst behind dividing the Slight. ....Eastern Louisiana... The newly issued Slight in eastern Louisiana is in place for an ongoing MCS that has a history of producing rainfall rates of 2-4 inches per hour, along with training and backbuilding that has allowed this heavy rainfall to occur over a small area for an extended period of time. On the whole the MCS has been weakening, but local cores with rates that high continue this morning. CAMs guidance is in reasonable agreement that some level of heavy rain from convection will continue in this area, likely north of Lake Pontchartrain, through 18Z. It appears likely that this Slight=20 will be able to be downgraded this afternoon with higher confidence in the convective trends. ....Northeast Texas... The southern end of the previous Slight has been expanded south and east in response to a much more robust MCS (compared to the one in Louisiana) across northern Texas this morning. Individual cores of heavy rain have been far more persistent into the late morning, and have developed into an east-west oriented line that is now generally south of the I-20 corridor, and fortunately well south and west of the Dallas-Fort Worth Metroplex. While urban concerns remain heightened in the Metroplex for the possibility of additional storm development this afternoon, the greatest near term concerns will be between I-20 and I-35 in central Texas. With peak heating, expect additional storms to develop south of the current storms in the area of greatest inflow of moisture and instability. ....Kansas to Iowa... Multiple small clusters of storms from northern Kansas through=20 central Iowa are largely weakening this morning. However, there is some CAMs consensus that additional strong convection will break out in southeast Nebraska this afternoon. This convection will=20 advect northeast into Iowa, where previous rounds of heavy rain have depressed FFGs. Thus, despite a lower likelihood of training and faster moving cells, the low-confidence Slight remains in place with a small expansion northeast further into central Iowa based on the trends in the guidance. There remains some possibility tonight that additional convection will fire along remnant outflow boundaries in northern Kansas where the current line of showers has already cleared, which is why for now the Slight remains for that area. ....Marginal Risk... Elsewhere, as mentioned above expect a relative minimum of convection over most of Oklahoma and southern Kansas today and tonight, though isolated cells remain very possible. For the Southeast, no changes were made, with expected individual cells or small clusters of storms developing this afternoon with peak heating. The coverage of storms in this area is unlikely to be very robust, precluded the need for a Slight Risk upgrade for now. Wegman Day 2 Valid 12Z Fri Apr 25 2025 - 12Z Sat Apr 26 2025 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS, MID-MISSISSIPPI VALLEY, OHIO VALLEY, AND PORTIONS OF THE NORTHEAST... A strengthening surface low developing ahead of a strengthening upper level shortwave trough will drive the storms from a forcing standpoint through the period. Starting in the Plains it will track northeast into the Great Lakes Friday evening, with showers and storms forming along the cold front to the south and east of the low center. This will bring periodically heavy rainfall to portions of the Northeast, which has been in a drier period the past week. Gulf moisture continuing to advect in from the south will lead to shower and thunderstorm activity starting Friday afternoon across the Tennessee and Ohio Valleys, and continuing into Friday night as the front lags behind (south and west) of the surface low. Meanwhile, the trailing (western) end of the cold front may be the trigger for additional thunderstorms into southern Oklahoma, north Texas, and the southern Texas Panhandle. In coordination will the offices in the Northeast the Marginal Risk was removed from New Hampshire, Vermont, much of New York and northeast Pennsylvania. This area has been drier of late and with green up already in progress, much of the rain will be absorbed with minimal if any flooding possible. Elsewhere, the Marginal had minor reshaping to reflect the latest WPC QPF and model trends. Campbell/Wegman Day 3 Valid 12Z Sat Apr 26 2025 - 12Z Sun Apr 27 2025 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS AND FOR PORTIONS OF NEW ENGLAND... ....New England... Showers and thunderstorms are expected to pass through New England thanks to upper level shortwave energy and wavy surface fronts. The flow is expected to be fairly progressive so it will help limit the potential for flash flood. Given the recent QPF trends and placement, the inherited Marginal Risk area was significantly modified to only include northeast Vermont, northern New Hampshire and the majority of the state of Maine. ....Southern Plains... The steady influx of rich moisture ahead of a deeply strengthening storm system ejecting into the Plains will fuel rounds of heavy rain and thunderstorms across portions of the central U.S. from the weekend into next week. Guidance has improved its focus on where the higher QPF will occur. The old Day 4 Marginal Risk was reduced out of Nebraska and Kansas, now spanning from Texas to western Arkansas as the new Marginal Risk area for this period. Heavy rain will be favorable with the upper trough diffluence combined with front/dryline instabilities. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!53Z3_ZXfuqqWIKCcZW6uvrFfLEZ_l7GWquugYHYLJli2= rBemngICvubmNiBvKJJe-vhQeBc8LF6--PP1e_bH-w16tt0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!53Z3_ZXfuqqWIKCcZW6uvrFfLEZ_l7GWquugYHYLJli2= rBemngICvubmNiBvKJJe-vhQeBc8LF6--PP1e_bHaSfndrM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!53Z3_ZXfuqqWIKCcZW6uvrFfLEZ_l7GWquugYHYLJli2= rBemngICvubmNiBvKJJe-vhQeBc8LF6--PP1e_bHgu7OdcM$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .