Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 28 2025 08:29:50 FOUS30 KWBC 280829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 AM EDT Sat Jun 28 2025 Day 1 Valid 12Z Sat Jun 28 2025 - 12Z Sun Jun 29 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS=20 OF THE PLAINS INTO THE MID ATLANTIC/NORTHEAST US... ....Northern Plains and Upper Midwest... Showers and thunderstorms capable of producing locally heavy=20 rainfall rates and heavy rainfall totals have the potential to produce flash flooding as the next upper shortwave trough approaches. Aided by a 90kt upper level jet streak on the lee=20 side...the upper trough will generate a compact area of fairly=20 robust, transient deep-layer forcing over the outlook area later today and tonight. MUCAPEs are expected to soar within the warm=20 sector prior to the surface cold frontal passage. Given=20 precipitable water values getting near 1.75 inches...storms which=20 form within the unstable airmass will be capable of producing=20 rainfall rates in excess 1.5 inches per hour and areal average=20 rainfall amounts of 1 to 3 inches...especially once low- level=20 inflow accelerates to between 30 kts and 40kts at 850 mb ahead of=20 the approaching front. The storm/mesoscale nature of the threat=20 leads to uncertainty of a more focused corridor of higher risk, but a Slight Risk may still be necessary...particularly over the Upper Mississippi Valley...if trends remain consistent. ....Mississippi Valley to the Mid Atlantic/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 inches and as weak mid-level shortwave energy aids convective development in a high CAPE/weak flow environment over portions of the Mid- Mississippi Valley into the upper Ohio Valley. Farther north,=20 maintained the Marginal Risk to account for the possibility that some of the convective activity across southeastern Canada north=20 of the warm front clips portions of northern New England. While=20 guidance indicates the potential for 1-2" of rainfall totals across the region, the less robust convection on the northern side of the front should keep any flooding issues isolated. ....Southeast to adjacent southern Plains... Scattered pulse thunderstorms are expected across a broad warm=20 sector as seasonable instability develops with daytime heating from the Southeast and into the adjacent southern Plains. High=20 precipitable water values (at or above 2 inches, some 2 standard=20 deviations above the climatological mean for this time of year)=20 will once again lead to highly efficient rain rates of 1-2" per=20 hour, possibly as high as 3" per hour, which is more than enough to lead to isolated flash flooding concerns despite the generally=20 limited thunderstorm duration. With a signal that has persisted several runs...introduced a Marginal risk area over parts of the Florida peninsula for late day convection that fires along a weak convergence boundary. ....New Mexico... Yet another day of thunderstorms is expected across portions of southern New Mexico and west Texas with locally heavy rainfall (1-2") possible. QPF trends (coverage, intensity) are more isolated compared to day 1 with the moist south to southeast low-level upslope flow likely resulting in more localized areas of heavier rainfall focused across the Sacramento and Guadalupe Mtns south through the Trans-Pecos. The flash flood potential is expected to remain isolated. Bann/Putnam Day 2 Valid 12Z Sun Jun 29 2025 - 12Z Mon Jun 30 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL EXTENDING OVER=20 PORTIONS OF THE CENTRAL UNITED STATES... There is a Marginal Risk of excessive rainfall over portions of the central United States from the western Great Lakes south through the Mississippi Valley and west into the central/southern Plains and southern Rockies. Showers and thunderstorms are expected both along and well-ahead of a cold front and trailing surface trough/dryline as an upper-level trough approaches from the west. Mechanisms to help focus convection becomes less defined ahead of the front but deterministic guidance indicates widely scattered rainfall totals of 1-3" are possible 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.=20 Waves propagating along the front may help to focus/organize=20 convection and lead to a more concentrated threat...and remained=20 supported by localized maxima in the ensemble means/probabilities=20 in the central Plains/Missouri Valley to the Upper Mississippi=20 Valley region...confidence remained low with respect to the exact=20 placement. Bann/Putnam Bann Day 3 Valid 12Z Mon Jun 30 2025 - 12Z Tue Jul 01 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE WESTERN PLAINS EASTWARD INTO THE MID ATLANTIC... Similar to Sunday...convection is expected to develop within a region of decent CAPE and precipitable water values in excess of 2=20 standard deviations above climatology. Except for some mid-level westerly flow around the Great Lakes to provide some shear there...the flow farther south should be fairly meager (but offset by steeper low-level lapse rates). This sets up the potential for=20 some local rainfall rates in excess of 1 inch per hour that results in excessive rainfall from the Western High Plains=20 east/northeastward into the Ohio Valley and parts of the Mid- Atlantic region on Monday and Monday night. A weakening surface=20 boundary will help focus some of the threat for heavier rainfall=20 but its placement is quite uncertain. Without much forcing or confidence in placement of a boundary to focus activity...placement of any heavy rainfall is low confidence. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8AHabBRIwEOgRDFGByiIaYEekjsrgCrp489nLtt87VDz= NWfi_wj1YceW-w8aaHiIFP03xf3-cC0I5frlNjy4q7Fir3I$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8AHabBRIwEOgRDFGByiIaYEekjsrgCrp489nLtt87VDz= NWfi_wj1YceW-w8aaHiIFP03xf3-cC0I5frlNjy41L9L5y4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8AHabBRIwEOgRDFGByiIaYEekjsrgCrp489nLtt87VDz= NWfi_wj1YceW-w8aaHiIFP03xf3-cC0I5frlNjy4OoelV7o$=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) .