Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Feb 26 2024 00:29:38 FOUS30 KWBC 260029 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 728 PM EST Sun Feb 25 2024 Day 1 Valid 01Z Mon Feb 26 2024 - 12Z Mon Feb 26 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 2 Valid 12Z Mon Feb 26 2024 - 12Z Tue Feb 27 2024 ....2030Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 Valid 12Z Tue Feb 27 2024 - 12Z Wed Feb 28 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE OHIO VALLEY... ....2030Z Update... Few changes were made to the existing Marginal Risk area across the Ohio Valley. Latest guidance suggests the heaviest rainfall totals will be overnight Tuesday night/Wednesday morning across far northern Ohio, southeast Michigan, and northwestern Pennsylvania. As such, the Marginal was expanded a bit towards the northeast. A 60 kt LLJ is forecast in multiple pieces of guidance, including the GFS and EC, which will advect Gulf of Mexico moisture and instability northeastward ahead of a low and strong cold front racing east across the Plains. Much of the thunderstorm activity will be associated with the warm front and the LLJ behind it. Largely unidirectional southwesterly flow will favor the development of training thunderstorms in the Marginal Risk area. The strongest storms are expected on the western side of the Marginal Risk area as the storms are moving across Illinois and Indiana Tuesday afternoon and evening. By the time the storms reach eastern OH and western PA, the focus will be the leading edge of the LLJ and the warm front, resulting in a larger area, perhaps as an MCS of moderate to locally heavy rain. Expect more widespread 1 to 2 inch totals in this area, but less likely to see the extreme but highly localized rainfall totals more likely further west. The biggest factor working against flash flooding is the prevalent bone-dry conditions over the entire Marginal Risk area leading up to this event. This should allow added "space" for the rainfall to fill largely empty river basins. Nonetheless, the potential for heavy rainfall with the favorable atmospheric conditions should overcome the dry soils in isolated instances. The Marginal remains lower confidence. Some of the model guidance suggests heavier convection could develop further south towards the Ohio River itself, so there is some potential for additional expansions towards the river. Wegman ....Ohio Valley... A strong positively tiled mid-level trough is expected to sweep across the Central U.S. Tuesday/Tuesday night with a potent area of low pressure likely to intensify over the Great Lakes. A warm front draped across the region will act as the focus for elevated showers and thunderstorms as early as the afternoon hours, and likely continue through the night as a very impressive low-level jet ramps up where 850 mb winds reach 50+ kts. This warm/moist airmass will spark scattered/numerous showers and thunderstorms along the advancing cold front Tuesday night through early Wednesday morning. This system will have very strong dynamics and an increasingly moist airmass which may be supportive for locally heavy rainfall, particularly along the warm front where training/repeating rounds of rainfall are more likely. The storm motions are likely to be fast/progressive along and ahead of the cold front but may contain intense/brief rain rates. While there remains uncertainty in the placement/timing of the main features, the setup certainly favors strong thunderstorms and with the PWs increasing well above 1", some localized/isolated flooding issues will be possible so a Marginal Risk was introduced this cycle for portions of the Ohio Valley. Taylor Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7i5UOerkXzlNXCA8ayHRXe9eTj9WDlaGqRdbr4euDWjQ= 3M_htJP_o2MDSLCnGcFrYhLcX5Uc90KDNpqdRyL_zHr-gVM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7i5UOerkXzlNXCA8ayHRXe9eTj9WDlaGqRdbr4euDWjQ= 3M_htJP_o2MDSLCnGcFrYhLcX5Uc90KDNpqdRyL_KPBlLJA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7i5UOerkXzlNXCA8ayHRXe9eTj9WDlaGqRdbr4euDWjQ= 3M_htJP_o2MDSLCnGcFrYhLcX5Uc90KDNpqdRyL_xz6cLK8$=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) .