Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 27 2025 15:55:23 FOUS30 KWBC 271555 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1155 AM EDT Fri Jun 27 2025 Day 1 Valid 16Z Fri Jun 27 2025 - 12Z Sat Jun 28 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL APPALACHIANS... ....Central Appalachians... A more focused thunderstorm/heavy rainfall threat is expected=20 through the central Appalachians today as very moist flow interacts with the terrain ahead of a 'back-door' cold front passing through the Mid-Atlantic that will become quasi-stationary throughout the=20 day. Of particular concern is the prospect suggested by some of the 12Z hi-res guidance (HRRR and HREF) that initial storms over parts of western Maryland/West Virgina Panhandle/northwestern Virginia=20 will cluster/organize and move slowly southward along the=20 instability gradient ahead of the stalling front. Updated 12Z HREF=20 probabilities are between 40-60% for rainfall of 3"+, with a=20 focused area of 20-30% of 5"+ across the West Virginia Panhandle.=20 Efficient rainfall rates of 1-2.5" per hour can be expected given=20 PWATs upwards of 2" per 12Z PBZ sounding. Much of this region=20 remains more sensitive to additional rainfall not only due to the=20 typical terrain impacts but a number of recent heavy rainfall=20 events keeping FFGs low, with scattered to potentially numerous=20 instances of flash flooding possible.=20 ....Northern NY-New England... The suite of 12Z operational models and ensemble runs continues a=20 trend started during the day on Thursday of shifting the focus for=20 heavy rainfall to remain north of the international border. Even=20 though there are some variances on the possible MCS path which=20 could still result in an MCS clipping the northern portion of New=20 York and New England...it should fall in a region where Flash Flood Guidance is higher than adjacent areas so the Slight Risk was=20 removed and the Marginal Risk area was removed from the upper=20 Hudson Valley and southward. ....Southern Plains into the Mississippi Valley and Southeast... Another typical Summer day of scattered thunderstorms is expected=20 broadly from the Southeast through the Mississippi Valley and west=20 along a surface trough through the southern Plains given seasonable instability with daytime heating and a passing upper- wave. Pulse- type thunderstorms will have the ability to produce quick efficient bursts of heavy rainfall (1-3") and the risk for some mostly=20 isolated urban flooding, especially where any storms=20 develop/congeal along residual outflows.=20 ....Northern Plains... A quick moving shortwave across the northern and central tier of=20 the CONUS will lead to thunderstorm activity capable of locally=20 heavy rainfall, especially if convection can grow upscale into a=20 more organized MCS as indicated by some of the 12Z hi-res model=20 guidance. However, prospects for flash flooding still seem to be=20 limited given the progressive nature of the shortwave=20 trough/possible MCS. A quick 1-3+" is likely anywhere over parts of the eastern Dakotas and across central Minnesota. ....West Texas into New Mexico... Continued threat of widely scattered thunderstorms across far West Texas into New Mexico again over an area that will have seen=20 several days of heavy convective impacts with compromised Flash=20 Flood Guidance. Local 1- to 2-inch amounts are possible in the=20 period with the highest threat likely over the Sacramento's down=20 through the Guadalupe Mountains and adjacent valleys. A Marginal=20 risk was maintained to cover for the threat. Putnam/Bann Day 2 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... 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 mainly Saturday night. later in the period (especially Sat night). MUCAPEs are expected to soar within the warm sector prior to the surface cold frontal passage. Given precipitable water values getting near 1.75 inches...storms which form the unstable airmass will be capable of producing rainfall rates in excess of 1 inch per hour and areal average rainfall amounts of 1 to 3 inches...especially once low- level inflow accelerates to between 30 kts and 40kts at 850 mb ahead of the approaching front. ....Northeast... There continues to be an increasing concern for heavy to potentially excessive 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. ....New Mexico... Maintained a targeted Marginal Risk area over/near the Sacramento Mtns, particularly in vicinity of burn scars. QPF trends (coverage, intensity) are similar to Day 1, with the moist south to southeast 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. Bann Day 3 Valid 12Z Sun Jun 29 2025 - 12Z Mon Jun 30 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL EXTENDING OVER PORTIONS OF THE CENTRAL UNITED STATES... There is a Marginal Risk of excessive rainfall over portions of the central United States between the western Great Lakes and the Southern Rockies. Any showers or thunderstorms which form along or ahead of the front may be able to produce rainfall rates high enough to result in flash flooding. Away from the upper trough...mechanisms to help focus convection becomes less defined in an atmosphere characterized by precipitable water values in excess of 1.5 inches over all but the plains near the Central and Southern Rockies to in excess of 2 inches east of the Mississippi. Ensemble guidance depicted isolated to widely scattered rainfall amounts of 1 to 3 inches but little coherence in placement between the ensemble runs. Opted to highlight a broad but generally unfocused Marginal risk area . Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6_ApaL5lYdUKKXpNvyoerWIcnRAKxnQ6GzRs_7XL3h9C= lzDQpoG97RnPzFis3g5kuYLTQXRz5AfqbC0YxIBygCGuNtk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6_ApaL5lYdUKKXpNvyoerWIcnRAKxnQ6GzRs_7XL3h9C= lzDQpoG97RnPzFis3g5kuYLTQXRz5AfqbC0YxIByAvIpTVo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6_ApaL5lYdUKKXpNvyoerWIcnRAKxnQ6GzRs_7XL3h9C= lzDQpoG97RnPzFis3g5kuYLTQXRz5AfqbC0YxIBytrgzURU$=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) .