Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun May 25 2025 12:57:11 FOUS30 KWBC 251256 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 856 AM EDT Sun May 25 2025 Day 1 Valid 12Z Sun May 25 2025 - 12Z Mon May 26 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM CENTRAL OKLAHOMA TO NORTHWESTERN ARKANSAS... ....Southern Plains to the Mid-South/Tennessee Valley... Convection now developing over the central High Plain is expected to gradually grow upscale through the remainder of the overnight as it moves further east into a region of deeper moisture associated with a low level warm front. Storms will likely be ongoing, with areas of heavy rain impacting portions of southeastern Kansas, northeastern Oklahoma, and the Ozarks as this system crosses the region through the remainder of the morning into afternoon hours. Some storms may persist and reintensify as they move east of the Ozarks, bringing a heavy rain threat and some potential for flash flooding into the Mid-South and Tennessee Valley by the afternoon. A lingering boundary and moisture will help support redeveloping convection back to the west across Oklahoma into the Texas Panhandle by the afternoon. These storms are also expected to grow upscale as the low level jet across Texas intensifies ahead of an upper trough moving across the Southwest. Moisture pooling on the nose of the low level jet (PWs ~1.75 in) within a region of strong ascent is expected to support the development of a convective complex, with heavy rains moving east near the Red River through the overnight. Forecast confidence is limited by differences shown by the CAMs regarding how this convection will evolve and their placement of heaviest amounts. Relied on the HREF to make adjustments to the previous outlook, which included shifting the Moderate Risk area further south across central/eastern Oklahoma and western Oklahoma. With possible contributions from both this morning's activity and the storms expected to follow this evening and overnight, the HREF is showing some of its highest neighborhood probabilities for amounts over 3 inches over this area. This also corresponds with an area of relatively lower flash guidance, reflecting some locally heavier totals that have fallen over the past 24-hrs. Maintained the Slight Risk as far west as the eastern Texas Panhandle, where this second round is expected to become better organized this evening. Also brought the Slight Risk further south across Northeast Texas, where some of the guidance shows slow-moving, heavy rain producing storms developing along a boundary ahead of the system. ....Front Range into the Central High Plains... Anomalous moisture supported by low level easterly flow is expected to fuel additional showers and thunderstorms developing along the terrain before moving east, with some threat for locally heavy amounts and isolated flash flooding concerns. Easterly winds along the northern extent of a low centered over the southern High Plains will continue to support standardized PW anomalies over 1.5 sigma, which along with daytime heating and ascent afforded by a mid- level shortwave and right-entrance region forcing is expected to support storm development. A Marginal Risk was maintained from the Front Range eastward into southwestern Nebraska, where the HREF is showing high neighborhood probabilities for accumulations over an inch, along with some notable probabilities for amounts over 2 inches along the high terrain. ....Florida and Georgia/South Carolina coasts... A stalled frontal boundary will remain across central Georgia and the SC Lowcountry. Southerly flow along the western extent of the subtropical ridge will support deepening moisture along and south of the boundary, reaching ~1.75 inches in some locations. This moisture along with daytime heating and enhanced convergence along land-sea interactions, will support showers and thunderstorms capable of producing locally heavy rates and perhaps isolated flash flooding concerns, especially in urbanized areas. A Marginal Risk was drawn for areas from the SC Lowcountry to South Florida, where the HREF shows high neighborhood probabilities for accumulations exceeding 2 inches. Pereira Day 2 Valid 12Z Mon May 26 2025 - 12Z Tue May 27 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE SOUTHERN PLAINS TO THE TENNESSEE VALLEY... Overall, not much change to the previous forecast. The shortwave associated with the previous night's convection over the Southern Plains is expected to move out across the Mississippi Valley into the Mid-South. This along with trailing energy moving from the Southwest into the Plains will help shift the axis of deeper moisture and the greater potential for heavy rainfall further south and east. Expect the initial wave to carry with it some threat for heavy rain and flash flooding into the Mid-South and the TN/lower Ohio Valleys as it helps direct deeper moisture into the those regions late Monday into early Tuesday. However, perhaps the bigger threat for heavy rain and possible flash flooding will focus further to the southwest along a boundary left in the wake of this system. Southerly flow ahead of a wave moving across the Southern Plains maintaining deep moisture, along with right-entrance region upper jet forcing providing large scale ascent, are expected to generate an environment favorable for heavy rainfall. Some of the overnight guidance continues to show impressive amounts extending across parts of Northeast Texas into the ArkLaTex. There is still enough uncertainty to withhold an upgrade to a Moderate, but will continue to monitor. Pereira Day 3 Valid 12Z Tue May 27 2025 - 12Z Wed May 28 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL EXTENDING FROM THE SOUTHERN PLAINS TO THE MID ATLANTIC AND SOUTHEAST... An expansive Marginal Risk was maintained from areas along and east of the central/southern Appalachians back through the Ohio, Tennessee, and lower Mississippi valleys and across Texas. While one or more Slight Risk are likely forthcoming within this broad area, opted to maintain the Marginal pending better model agreement and forecast confidence in future runs. Areas for potential upgrades include the upper Ohio Valley, where some models show heavy amounts associated with energy moving out of the central U.S. and across the top of a downstream ridge. Another possible area is over the Tennessee Valley into the Southeast, where energy moving out of the lower Mississippi Valley, along with favorable upper jet forcing, may contribute to some higher totals. Perhaps a more likely area will be associated with some of the deeper moisture and greater instability back across South-Central Texas. Some, but not all of the guidance, show mid-level energy along with right-entrance region upper jet dynamics supporting heavy amounts across the region Tuesday afternoon into the evening. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!__1a8CVzJtmLpEdUeriOh49UIKr0oj6TN5rU21Q5umPs= e8idovqhdPtcaXFPe3q6okJqkG61PWvhwhfSMTMHu23u4bk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!__1a8CVzJtmLpEdUeriOh49UIKr0oj6TN5rU21Q5umPs= e8idovqhdPtcaXFPe3q6okJqkG61PWvhwhfSMTMHviOXnHE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!__1a8CVzJtmLpEdUeriOh49UIKr0oj6TN5rU21Q5umPs= e8idovqhdPtcaXFPe3q6okJqkG61PWvhwhfSMTMH16eOVNc$=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) .