Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Feb 26 2024 08:18:17 FOUS30 KWBC 260818 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 317 AM EST Mon Feb 26 2024 Day 1 Valid 12Z Mon Feb 26 2024 - 12Z Tue Feb 27 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer Day 2 Valid 12Z Tue Feb 27 2024 - 12Z Wed Feb 28 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE OHIO AND MID-MISSISSIPPI VALLEY'S... A robust mid-level shortwave will propagate southeast out of the Pacific Northwest on Tuesday with increasing difluent flow ahead of the mean trough that will help initiate a round of convection within the confines of the Mid-Mississippi and Ohio Valley's. Focused meridional flow ahead of the mean longwave trough will advect deeper moisture and associated theta-E's poleward with a tongue of elevated instability building within the areal theta-E advection regime. Getting more into the hi-res time frame, we are seeing some forecast MUCAPE values approaching 500-1000 J/kg with locally higher lying along a projected warm front situated to the east of a developing surface reflection in the central Midwest. PWAT indices soar to 2-3 standard deviations above normal within a large zone spanning from the Mid-Mississippi Valley up into the Great Lakes by Tuesday afternoon as the enhanced low and mid-level flow usher Gulf moisture into the outlined area. By late-Tuesday afternoon, convective development is likely thanks to the approach a mid-level vorticity maxima moving out ahead of the shortwave trough as it migrates eastward. Models are keying on a band of heavy rainfall within the proximity of a warm front, denoted fairly well within the theta-E fields on guidance. The question that still needs to be solved is where that boundary will lie. Current consensus is north of I-70 with some guidance as far north as southern MI which leads this to be the focal point of expected convective development. Recent HREF probability fields for at least 1"/hr have risen to 25-30% within the confines of the IN/MI/OH border which is where most of the CAMs currently have the warm front situated when examining the surface moisture/temp fields. Further south will have the best deep layer moisture and elevated PWATs, but the lack of a focused boundary like the warm front in question will lead to more isolated flash flooding concerns, mainly within urbanized areas, and terrain as you head further east. Any convective development will continue into the overnight hours as we approach Wednesday with upscale growth of convection likely after 06z as the shortwave trough pivots east of the Mississippi and begins to take on a more neutral tilt by the end of the period. Large scale forcing will be at its maximum by the end of the forecast cycle with a line of heavy rain likely extending from eastern OH, south into the Tennessee Valley. This will continue to advance eastward and the focus shifts into the Appalachian front and terrain-centric areas in the Mid-Atlantic and Ohio Valley as we roll into D3. The Marginal Risk from the previous forecast was maintained, but adjusted to reflect the latest QPF trends within the convective-allowing environment being forecast. A Slight Risk upgrade is non-zero, but current forecasted rates within any convection keep this capped for the time-being. Kleebauer=20 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!60FkGRkcIprBwaiKeVHMcDcddzN0lFrZEI8ib3Ekw1ol= 9E-KIKi3kCbv0UDvOQpyzoo2lDAg1D7QS2OHRX5yHXBUoXA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!60FkGRkcIprBwaiKeVHMcDcddzN0lFrZEI8ib3Ekw1ol= 9E-KIKi3kCbv0UDvOQpyzoo2lDAg1D7QS2OHRX5yRUZTs-E$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!60FkGRkcIprBwaiKeVHMcDcddzN0lFrZEI8ib3Ekw1ol= 9E-KIKi3kCbv0UDvOQpyzoo2lDAg1D7QS2OHRX5y0gDLut0$=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) .