Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 27 2025 00:49:46 FOUS30 KWBC 270049 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 849 PM EDT Thu Jun 26 2025 Day 1 Valid 01Z Fri Jun 27 2025 - 12Z Fri Jun 27 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE CENTRAL PLAINS, MIDWEST, & GREAT LAKES... An upper level trough will pivot eastward across the Upper MS=20 Valley and Upper Great Lakes region Thursday night into early Friday. Enhancing the deep-layer forcing will be the curved 90kt=20 upper level jet streak that will be skirting the U.S.-Canadian=20 border. Ahead of the upper shortwave trough/surface front --=20 850-700 mb moisture flux anomalies are noteworthy (1.5-2.0 standard deviations above normal), as is the 0-6km bulk shear values=20 (35-45+ kts). This will likely continue to support more widespread, organized convective line segments into the overnight across the=20 elongated Slight Risk area, with embedded mesocyclones possible.=20 When compared to continuity, cleared the former western portions of the risk areas based on radar reflectivity trends and 18z HREF=20 output. ....Mid Atlantic & Upper Ohio Valley...=20 Relatively light (generally 20kt or less) deep-layer shear with=20 a near upper level high overhead between a retrograding TUTT cell in the Southeast and Westerlies to the north has caused a Florida- like situation to unfold today, with outflow boundaries moving in from many directions of the compass, which has caused CIN to set in across much of the region. The most interesting aspect has been a synoptically enhanced sea breeze, a possible cold front that=20 cleared portions of the Eastern Shore this afternoon and evening=20 and has led to patches of stratus in its wake over portions of NJ=20 & DE. The 18z HREF has significantly overforecast early evening=20 convection in the DC area in the hours leading up to this=20 discussion's issuance. With convective coverage becoming more=20 isolated due to the broad CIN development, dropped the risk in the=20 region to Marginal. The 18z HREF indicates that the threat of heavy rainfall on an isolated basis should end by midnight, holding on=20 the longest across portions southern PA, the Virginias, and near=20 the shores of Chesapeake Bay. ....New Mexico... Isolated to scattered thunderstorms across the Southern High Plains and the Texas Big Bend should maintain at least some threat for=20 flash flooding given wet antecedent conditions following a wet=20 multi-day convective period. Remaining elevated moisture and=20 sufficient buoyancy will maintain the diurnally driven=20 thunderstorms through roughly 05z, based on the 18z HREF output.=20 Heaviest thunderstorms will be capable of 1-2" with the peak QPF=20 max probably closer to 3". The previous MRGL risk was maintained, but trimmed on its western side per radar trends and the 18z HREF output. Roth/Hurley Day 2 Valid 12Z Fri Jun 27 2025 - 12Z Sat Jun 28 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NORTHERN NEW YORK AND NORTHERN NEW ENGLAND... ....Northern NY-New England... 21Z update... the latest guidance maintains the scenario described below with similar QPF amounts, particularly from northeast New=20 York to northern Vermont, therefore the Marginal and Slight Risk=20 areas were maintained as is. Campbell The forecast for a focused corridor of heavy rainfall associated with an MCS and trailing convection crossing from southeastern Canada into portions of Update New York/northern New England remains on track. While there are expectedly some variances on the possible MCS path which add some east-west uncertainty, all guidance is still in good agreement that the track will clip areas south of the international border bringing an attendant flash flood threat. Deterministic guidance indicates the potential of rainfall totals between 1-3", with ensemble probabilities of 2"+ between 15-25%. A small eastward adjustment of the Slight Risk area was added based on these latest ensemble probabilities. Elsewhere, prior forecast has remained consistent. ....Northern Plains... 21Z update... The progressive nature of the expected shortwave will help limit the severity of any local flooding that arises. The Marginal Risk currently in place remains without any changes at this time. Campbell A quick moving shortwave across the North-Central tier of the CONUS will lead to scattered thunderstorm activity capable of locally heavy rainfall and flash flood prospects. The best threat will be over Northern ND into the Red River area where some urbanized zones will have a greater threat for flash flooding. A quick 1-3+" is likely anywhere over Central ND into Northwest MN. This threat is within the lower end of the MRGL risk threshold and will be monitored closely to see if the risk is warranted, or needs any expansion. ....West Texas into New Mexico... 21Z update... The threat for localized heavy rainfall remains spotty across the area given the pattern. The Marginal Risk area continues to highlight the locations that may have local flash flooding during this period. Campbell Continued threat of widely scattered thunderstorms across far West TX into NM will allow for isolated flash flood concerns over areas that will have seen several days of heavy convective impacts with compromised FFG's. Local 1-2" is possible in the period with the highest threat likely over the Sacramento's down through the Guadalupe Mtns. and adjacent valleys. A MRGL risk was maintained to cover for the threat. Day 3 Valid 12Z Sat Jun 28 2025 - 12Z Sun Jun 29 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN PLAINS AND UPPER MIDWEST, THE NORTHEAST, AND SOUTH-CENTRAL NEW MEXICO... ....Northern Plains and Upper Midwest... 21Z update... The latest guidance continues to signal the highest QPF amounts to be over central Minnesota into western/northern Wisconsin with areal averages of 1 to 3 inches with locally higher amounts still possible. The environment looks to remain favorable for repeating cells, thus maintaining an elevated threat for localized flash flooding. Campbell Next approaching upper shortwave trough, with a 90kt upper level jet streak on the lee side, will generate a compact area of fairly robust, transient deep-layer forcing over the outlook area later in the period (especially Sat night). MUCAPEs are expected to soar within the warm sector prior to the surface cold frontal passage -- i.e. aoa 4,000 J/Kg per the GFS. This along with PWs getting near 1.75" will lead to more organized, widespread convection by Saturday night as the activity likely grows upscale with the increasing pre-frontal low-level inflow (30-40kts at 850 mb). The 00Z guidance indicates significant latitudinal spread in the heavier QPF, and as a result, have maintained the Marginal Risk from yesterday's Day 4 ERO. However, the potential for an upgrade to Slight is certainly plausible given the kinematic and thermodynamic profile, especially after 00Z Sun when the Corfidi Vectors decrease to 10kt or less (thereby enhancing the risk for cell training). ....Northeast... 21Z update... There is an increasing potential for heavy rainfall to develop across western Pennsylvania and surrounding areas as the frontal boundary sags southward and taps into the pooled PW values of 1.5-2". The latest model guidance are showing local maximums upwards of 2 inches possible and the ERO first guess supports expanding the Marginal Risk from eastern Pennsylvania further west into eastern Ohio, West Virginia and western Maryland. Campbell Upper shortwave trough pushes across the Northeast by late Sat, then off the coast Sun morning. The bulk of the rainfall will fall during the first half of the period (during the day Sat), coinciding with the most favorable pre-frontal deep-layer instability and moisture (PWs 1.75-2.00+ inches). The 00Z guidance shows considerable spread with the heaviest QPF, though are fairly similar with the max totals (1.5-3.0"). Given the spread in the model QPFs, along with the progression of the front and fairly quick diminishment in instability after 00Z Sun, for now will maintain the Marginal Risk. ....New Mexico... 21Z update... No changes were made to the Marginal Risk area. Campbell Maintained a targeted Marginal Risk area over/near the Sacramento Mtns, particularly the burn scar areas from the 2024 fires (Blue 2, South Fork, and Salt burn scars). QPF trends (coverage, intensity) are similar to Day 2, with the moist S-SE low-level upslope flow likely resulting in a concentrated area of heavier rainfall across the Sacramento Mtns and eastern foothills. The flash flood potential is expected to remain isolated/localized. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6BKAZzJ368AWHYuruuCGKuI3ZdH4XPh2dqqvVvy_7tqG= F7irjNEG5P0TZVuXbH0CK8Cy9om0Eaj2kpmi4rD5otEkBWU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6BKAZzJ368AWHYuruuCGKuI3ZdH4XPh2dqqvVvy_7tqG= F7irjNEG5P0TZVuXbH0CK8Cy9om0Eaj2kpmi4rD5ecBhPcA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6BKAZzJ368AWHYuruuCGKuI3ZdH4XPh2dqqvVvy_7tqG= F7irjNEG5P0TZVuXbH0CK8Cy9om0Eaj2kpmi4rD51MsDtwo$=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) .