Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Apr 21 2023 00:48:42 FOUS30 KWBC 210048 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 847 PM EDT Thu Apr 20 2023 Day 1 Valid 01Z Fri Apr 21 2023 - 12Z Fri Apr 21 2023 ......THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF EASTERN TEXAS TO THE MID-SOUTH... The greatest concentration of flash flood warnings thus far this afternoon/evening has been across portions of east central TX. This training/backbuilding threat will continue a bit longer, but in general the expectation is that this will evolve into forward propagating convective line tonight. This line of convection will still be capable of very heavy rainfall rates and localized flash flooding, but the expected forward speed should limit duration and thus coverage of flash flooding as the evening/night progresses. The other area to watch overnight will be northeast Texas into Arkansas, where multiple rounds of storms and/or backbuilding could result in an increasing flash flood risk. The initial band of convection continues to push off to the east ahead of the actual frontal boundary. Lower level moisture transport and convergence persists back to the west behind this initial area of convection...and there is plenty of upstream mid/upper forcing still to move across this region. The combination of this slow moving and lagging front and increasing synoptic ascent should result in the persistence or additional convective development over this region into the overnight. The biggest question mark will be how much instability is eroded and thus how much CAPE the next round of storms will have to work with as the night progresses. At this point do think we'll see enough lingering instability to support some continued heavier convection and rainfall rates into the overnight hours, with localized swaths of 3-5" of rainfall possible before the night is over. This should be enough to result in an increasing isolated to scattered flash flood risk over portions of AR, possibly extending into portions of southeast MO and adjacent portions of IL/KY/TN as well. Chenard Day 2 Valid 12Z Fri Apr 21 2023 - 12Z Sat Apr 22 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR A PORTION OF THE LOWER MISSISSIPPI RIVER VALLEY... Organized pre-cold frontal convection should be ongoing and near the central Gulf Coast around 12Z Friday as it continues tracking east or southeast. Deep Gulf-sourced moisture will continue to be drawn northward ahead of the front to fuel showers and thunderstorms with increasing confidence that the strongest moisture convergence will be over southern Louisiana where PWs reaching 2 inches are 2 sigma above normal. Flow in southern Louisiana will also be a little less than farther north. However, areas in the Mid-South will have deep-layer flow more parallel to the approaching cold front bringing a risk for repeating activity over western Tennessee/northwest Mississippi. There was consideration of focusing the Slight Risk area farther north over the Mid-South and removing the southern portion in Louisiana. However, uncertainty on the progression of the overnight activity seen in the 18Z HRRR and NAMnest warranted keeping the full Slight Risk area where there is potential for 2 to 4 inches. Farther north, greater progression allows the Marginal Risk to be shifted east over more of Ohio and Kentucky where there is a risk for 1 to 2 inches. Jackson Day 3 Valid 12Z Sat Apr 22 2023 - 12Z Sun Apr 23 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN MID-ATLANTIC... A plume of sub-tropical moisture spreading up the Eastern Seaboard on Saturday is focused fairly well over the southern Mid-Atlantic. While most global guidance brings a general risk of 1 to 2 inches to much of the Mid-Atlantic, the 12Z Canadian runs do focus QPF in excess of 2 inches near the existing Marginal Risk in southeast Virginia and Northeast North Carolina. Therefore, the Marginal Risk was maintained with a bit of an expansion over the relatively more flood prone Hampton Roads metro. Fairly dry antecedent conditions may allow this risk area to be dropped on subsequent shifts should the heavy rain focus become less certain. Jackson Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9Nq8M9zb7gw2meWOEYbk39EsEWqEGNxrGgUG3RCyfGvm= KkFU9TmH9wyv6nzAigYWH7AGaTj-DiPXNeAL95L7rk4wS18$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9Nq8M9zb7gw2meWOEYbk39EsEWqEGNxrGgUG3RCyfGvm= KkFU9TmH9wyv6nzAigYWH7AGaTj-DiPXNeAL95L7bO2pD0c$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9Nq8M9zb7gw2meWOEYbk39EsEWqEGNxrGgUG3RCyfGvm= KkFU9TmH9wyv6nzAigYWH7AGaTj-DiPXNeAL95L7ZVZuCEg$=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) .