Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 22 2025 00:10:12 FOUS30 KWBC 220010 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 810 PM EDT Fri Mar 21 2025 Day 1 Valid 01Z Sat Mar 22 2025 - 12Z Sat Mar 22 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 2 Valid 12Z Sat Mar 22 2025 - 12Z Sun Mar 23 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Roth/Wegman Day 3 Valid 12Z Sun Mar 23 2025 - 12Z Mon Mar 24 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE MID-SOUTH, SOUTHEAST, WEST VIRGINIA, & WESTERN WASHINGTON... ....Lower Mississippi and Tennessee Valleys... A progressive, strong cold front trailing from a deep low tracking across the Upper Midwest will be the primary focus for shower and thunderstorm activity in this area on Sunday. Due to the strength of the upper level system driving the front forward, divergence exists aloft in the front's vicinity. The pre- frontal southwesterly low-level jet will be parallel to the orientation of the front (southwest to northeast), which could support training of the leading convection. While the forward speed of the front slows as the parent cyclone gets more distant, it should move fast enough to limit training potential. While FFGs decrease markedly towards the north into the Ohio Valley, the lack of atmospheric instability in that region will keep most of the rainfall in that area to stratiform rain. While minimal instability outside of southern KY limits the northward extent of the risk area, recent GFS runs suggest that a new Marginal Risk was prudent across portions of WV, where flash flood guidance values remain relatively low -- ~1.50"/3 hours -- and frontogenesis may be able to allow rainfall amounts to challenge the 3 hourly FFG. The greater instability and moisture will be closer to the Gulf, though precipitable water values are expected to remain under 1.5" regionally, which brings into question the degree of convective coverage expected. The flooding threat will be partially offset by the higher FFGs in the lower Mississippi Valley, so between that and the forward speed of the front, instances of flash flooding should remain isolated and most likely across urban areas. The above favors a continuation of the Marginal Risk across portions of the Mid-South and Southeast. ....Western Washington... A strong trailing cold front will move into the coast of the Pacific Northwest on Sunday. Low-level inflow from the Pacific towards 50 kts with near zero MU CAPE will allow IVT values to peak around 600-650 kg/ms. This would also allow hourly rain totals to be close to 0.5", which could be problematic in any burn scars. Soils along the westward facing slopes of WA are well saturated from repeated rounds of rain over the past few weeks, so this round could result in flooding on the rivers, streams, and creeks that drain the Olympic Mountains, particularly the Skokomish. As freezing levels rise, the western slopes of the Cascades should be equally in the mix for higher rainfall amounts, so looped the Marginal Risk farther inland to encompass that area. Expect 2 to 4 inches of new rainfall in the area through the day on Sunday. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8g5zQkDZge00KxCy8Y2Snv_-FiWBfGFqpj-xCzHaOsRT= eodKHtXHn64lo42fk754R8488USWuegqhgZIeGznZR3kVIs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8g5zQkDZge00KxCy8Y2Snv_-FiWBfGFqpj-xCzHaOsRT= eodKHtXHn64lo42fk754R8488USWuegqhgZIeGznKS0ONnA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8g5zQkDZge00KxCy8Y2Snv_-FiWBfGFqpj-xCzHaOsRT= eodKHtXHn64lo42fk754R8488USWuegqhgZIeGznTufktoE$=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) .