Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 07 2025 15:22:11 FOUS30 KWBC 071520 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1120 AM EDT Sat Jun 7 2025 Day 1 Valid 16Z Sat Jun 07 2025 - 12Z Sun Jun 08 2025 ....THERE IS A RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE EASTERN UNITED STATES...WITH SLIGHT RISKS IN SOUTHERN NEW ENGLAND... THE OHIO RIVER VALLEY...AND MID-SOUTH... An active day of heavy rainfall and flash flooding is expected across a large portion of the eastern United States, with the Marginal Risk area now encompassing the majority of the land area in the CONUS east of 95W longitude. This is due to a broad region of near to above normal tropospheric moisture (via PW anomalies) and sufficient instability for convective rain bands and thunderstorms. Generally, the broad zone of heavy rainfall risk can be divided into three main areas of concern, all indicated by a regional-scale Slight Risk maximum now: 1. In the Northeast, where low-topped convection has organized into narrow bands of efficient heavy rainfall. MRMS analysis indicates almost no ice present in these convective bands, with 30 dBZ echo tops generally shy of the -10C level. In other words, warm rain processes are dominant and any organized convective rain band could produce localized heavy rainfall. The area of greatest concern is probably from active area of flash flooding in the Hudson Valley near Albany, NY eastward through Massachusetts and northern Connecticut to the Boston metro area. There should naturally be=20 increasing low-level convergence with the existing front draped=20 across the region, and increasing easterly flow near the coast=20 around the north side of the offshore low. Aloft, a coupled jet=20 structure should lead to enough divergence to focus convection. 2. The Ohio River Valley region, particularly the middle and upper Ohio Valley from late this afternoon well into the overnight hours. This will be due to scattered convective rain bands and perhaps some thunderstorms developing in advance of an eastward propagating mid-upper level wave, and developing surface low by this afternoon, currently centered over IA- MO. This should allow for some organized convective bands in the warm air advection regime. Model forecast soundings show increasing PWs to near or above the 90th percentile for early June and tall, skinny CAPE profiles that are a good match for efficient, low-topped convective flash flood events. Of particular concern will be the potential for flash flooding overnight in the central Appalachian region from eastern Kentucky and southeast Ohio into West Virginia and southwest Pennsylvania. Models show southwest low-level inflow increasing into the mountains in a very moist environment, with the right entrance region of an upper level jet streak providing divergence aloft. All of this should support an organized heavy rain threat and the structure of the instability profile will keep convection low- topped and dominated by warm rain processes. Locally significant flash flooding will be possible given the terrain in the area and relatively wet antecedent conditions. 3. Across the mid-South where a forward propagating MCS has already generated some flash flooding in central Arkansas, but appears to begin accelerating. Renewed development and/or stalling and training will be possible along the southern periphery of the cold pool later today, and hi-res models do show localized corridors of heavy rainfall that would be sufficient to cause flash flooding. The Slight Risk was shifted south to account for observational trends indicating the current position of the cold pool and convective line, and the projected motion over the next few hours. Lamers Day 2 Valid 12Z Sun Jun 08 2025 - 12Z Mon Jun 09 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS NORTHERN TEXAS AND SOUTHERN OKLAHOMA... ....Southern Plains to the Southeast... The latest guidance remains consistent in showing additional shortwave energy pushing east southeastward late Sunday afternoon/evening from the lee of the Central to Southern Rockies into the Southern Plains in the northwest flow on the south side of a stronger upper level low centered over the north-central United States. This will again re-strengthen the low level flow into the west to east oriented front forecast to remain across the Southern Plains, supporting another round of organized convection along the front. There continues to be fairly good agreement on the potential for an axes of heavy precip day 2, resulting in good continuity with the slight risk area with only some small changes to reflect the latest forecasts. This next round of organized convection will likely be fairly progressive, similar to what occurred farther to the north Thursday night into early Friday and Friday night into early Saturday. Still, there is likelihood of widespread rainfall amounts of 1-2" with localized amounts up to 4". Soils are not as saturated as areas farther north, but localized runoff issues are still likely. ....Central Appalachians into the Mid-Atlantic... The negatively tilted shortwave coming out of the OH Valley late day 1 will push across the Central Appalachians into the Mid- Atlantic day 2. There is a fair amount of spread with model qpfs, but a signal for the potential for locally heavy rains in the continued well defined area of upper difluence ahead of these height falls in an axis of above average PW values...1.5 to 2+ standard deviations above the mean. There were only some minor changes made to the previous marginal risk across the Central Appalachians into the Mid- Atlantic, continuing to center it across areas that have lower ffg values. Oravec Day 3 Valid 12Z Mon Jun 09 2025 - 12Z Tue Jun 10 2025 ....THERE IS A MARGINAL OF EXCESSIVE RAINFALL ACROSS THE SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, NORTHEAST THROUGH THE TENNESSEE VALLEY, UPPER OHIO VALLEY AND INTO THE EASTERN GREAT LAKES... There is good agreement in the latest guidance with the slow eastward push of the closed low through the Upper Lakes day 3 and the broad upper troffing extending south of this center through the MS and OH Valleys. A broad region of above average PW values will continue to stretch across the southern tier from the Southern Plains, east across the Lower MS Valley and into the Southeast along and ahead of the lead west to east oriented front. Another axis of above average PW values will push northeastward across the TN and OH Valleys into the Lower Lakes ahead of a secondary front rotating through the cyclonic flow on the southeast side of the strong closed low over the Upper Lakes. Along each frontal boundary, widespread moderate to locally heavy precip totals are likely. Model agreement, however, is not great with placement of maximum amounts, leading to overall low confidence in where anything but a marginal risk could be drawn. Overall, the previous broad marginal risk area fits well with the latest model qpf spread, with no significant changes made to previous outlook for the new day 3 outlook. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!94whDg0a3KxU9mSepEt5Ayah1gNWktqb4fyc8EsEhmGZ= 6xgXeBa166o6u_DnoHLf6fed6JvbbW5fq8IAbiNTcT5Ua6U$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!94whDg0a3KxU9mSepEt5Ayah1gNWktqb4fyc8EsEhmGZ= 6xgXeBa166o6u_DnoHLf6fed6JvbbW5fq8IAbiNTgJ_Zfug$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!94whDg0a3KxU9mSepEt5Ayah1gNWktqb4fyc8EsEhmGZ= 6xgXeBa166o6u_DnoHLf6fed6JvbbW5fq8IAbiNTq-WzF0A$=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) .