Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 26 2023 08:25:23 FOUS30 KWBC 260825 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 424 AM EDT Sat Aug 26 2023 Day 1 Valid 12Z Sat Aug 26 2023 - 12Z Sun Aug 27 2023 ....A MARGINAL RISK OF EXCESSIVE RAINFALL IS IN EFFECT FOR PORTIONS THE SOUTHERN-CENTRAL ROCKIES AND CENTRAL PLAINS EASTWARD INTO PARTS OF THE LOWER MISSOURI AND MID MISSISSIPPI VALLEYS AS WELL THE TENNESSEE AND LOWER OHIO VALLEYS... Maintained a corridor of a Marginal risk area across parts of Missouri east/southeastward across portions of the Tennessee Valley/lower Ohio Valley..with on-going moderate to heavy rainfall being on-going at the start of the outlook period followed by additional elevated convection forming along/near a quasi-stationary front in a region of weak upper level height/thickness diffluence between the contracting deep-layer ridge and digging upper trough. There still looks to be some enhanced forcing within the right-entrance region of a 70-90kt upper level jet streak traversing the Great Lakes region. Spaghetti plots from the SREF and GEFS still not showing much overlap of 1 or 2 inch contours with each other...although the HREF was beginning to show some clustering of 40 km neighborhood probabilities of 1 inch per hour from the Mid-Mississippi Valley into the Tennessee Valley by later this morning and probabilities of 2 inches of rain in an hours develop by afternoon, The signals are not that strong...generally 15 per cent or less. The overall threat for heavy rainfall gradually shifts eastward into the east end of the Tennessee Valley by late tonight. Made a few adjustments to the previously issued Marginal.=20 Day 2 Valid 12Z Sun Aug 27 2023 - 12Z Mon Aug 28 2023 ....THERE ARE MARGINAL RISK AREAS EXTENDING FROM PARTS OF THE ROCKIES-HIGH PLAINS EASTWARD TO THE SOUTHEAST-LOWER MID ATLANTIC REGION... ....Rockies and High Plains... Another round of widely scattered afternoon and evening convection is expected along and near the terrain from the Central/Southern Rockies. Deeper moisture is expected to be in place...setting the stage for a few of the cells to produce local downpours from parts of Wyoming into New Mexico. Precipitable water values of 0.8 to 1.2 inches across the northern and western portion of the outlook area to nearly 1.25 inches on the plains from far southeast Colorado into northeast New Mexico and adjacent areas of Texas. Thinking is that at least some spots may get rainfall intense enough to produce run off related problems...with recent burn scars..normally dry washes and arroyos being most vulnerable. ....Parts of the Southeast into the Lower Mid Atlantic Region... Maintained the Marginal risk area over the Carolinas despite shifts from the ECMWF towards the GFS idea of limited coverage of rainfall being confined near the coast. The overall synoptic pattern...of an upper level jet over the Mid-Atlantic region helping provide upper level support for lift in a region where precipitable water values will generally be in excess of 2 inches...suggests that a broader area of 1 to 2 inch amounts seems plausible especially in light of the ARW5 developing 800 to 1500 J per kg of CAPE with little surface based CIN. Later outlooks can adjust later as needed. Of particular interest was the appearance of some 2 to 5 inch QPF bulls eyes across parts of the Tennessee Valley in the latest guidance from the ECMWF/UKMET/CMC and to a lesser extent by the NAM. Extended the Marginal Risk westward in deference to the number of model signals. Still believe that even the wetter solution in the Carolinas will be handled well given the antecedent conditions with only isolated run-off problems from the most active convection...and that what falls on Day 2 will act to prime the area for additional rainfall on Day 3. Bann Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-kKRZp5fh5v005gTwbNPTPLIwHPvDhCYEUxmqCknSuAV= YSJRnHjsehCVcJj1jjs02AvxXqt0ibGCdVx-eHDGfPRsvYo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-kKRZp5fh5v005gTwbNPTPLIwHPvDhCYEUxmqCknSuAV= YSJRnHjsehCVcJj1jjs02AvxXqt0ibGCdVx-eHDGLd0ZZ5c$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-kKRZp5fh5v005gTwbNPTPLIwHPvDhCYEUxmqCknSuAV= YSJRnHjsehCVcJj1jjs02AvxXqt0ibGCdVx-eHDGrSaASQ0$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .