Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Mar 23 2023 00:57:21 FOUS30 KWBC 230057 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 856 PM EDT Wed Mar 22 2023 Day 1 Valid 01Z Thu Mar 23 2023 - 12Z Thu Mar 23 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF CENTRAL SOUTHERN CALIFORNIA... Scattered showers and thunderstorms are expected to continue into the evening across portions of Central and Southern California as cold air aloft and an upper trough associated with a remnant upper low move across the region. While widespread heavy amounts are not expected, brief periods of heavier rainfall rates, resulting in isolated runoff concerns cannot be ruled out. Therefore, the Marginal Risk was maintained across Southern California and extended north along the coast into Central California. Farther to the east, showers will continue to diminish as drier air sweeps across the Southwest. With additional significant accumulations not expected, the Marginal Risk was removed from Arizona. Pereira=20 Day 2 Valid 12Z Thu Mar 23 2023 - 12Z Fri Mar 24 2023 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL OVER A PORTION OF THE MID/SOUTHERN MISSISSIPPI VALLEY.. Introduced a Moderate Risk of Excessive Rainfall focused primarily from northeast Oklahoma into southwest Missouri. Still expect a steady stream of moisture from the Gulf of Mexico as a deep-layer trough ejects from the Southern Rockies and results in strengthening low level flow. Precipitable water values at or slightly greater than 1.5 inches reaches eastern Oklahoma by 24/00Z. At about the same time, upper level divergence from an upper level jet aids in surface low pressure forming along a quasi-stationary front extending from Oklahoma northeastward into the Ohio/Tennessee Valley. The Moderate Risk was focused mainly in/near the Ozarks where 850 mb flow accelerates to 40 kts or more overnight and results in increasing moisture flux convergence along the boundary. The 12Z HREF started to show some potential for 1- and 3-hour rainfall amounts to exceed the respective flash flood guidance thresholds in southwest Missouri around 24/00Z and persist into the overnight. In addition...there were a few signals in the HREF for 2 inch per hour rates in the same area. While this area is not as saturated as it was a couple of weeks ago...there is local concern given that ground conditions are still fairly moist. Latest ensemble guidance showed precipitable water values being (more than 2 std dev getting lined up nearly parallel to the surface front so the potential for moderate to locally heavy/excessive rainfall along the front extending. Opted not to extend the Moderate any farther east which has not had quite as much rainfall recently and is not quite as hydrologically sensitive. The previously issued Slight and Marginal Risk areas covered the area and only minor adjustments were made based on the latest QPF and model mass fields. It is expected that the risk of excessive rainfall will continue beyond the end of the Day 2 period. Bann Day 3 Valid 12Z Fri Mar 24 2023 - 12Z Sat Mar 25 2023 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL FROM THE OZARKS TO THE OHIO VALLEY... Maintained the Moderate Risk area without too many changes from the issuance at 0830Z. Showers and thunderstorms will persist from the day 2 period in proximity to the sprawling frontal boundary with moisture flux convergence increasing across parts of the Mississippi Valley and into the Ohio Valley as a surface low pressure with trailing cold front moves east across the Southern Plains. Precipitable water values will surge up to 1.5 inches into the Mississippi/Tennessee/Ohio Valleys...which is some (+2 to +2.5 standard deviations greater than climatology for late March.=20 Repeating storms will track across areas soaked from recent rains and will likely surpass local FFGs early into the Day 3 period. The latest guidance depicts several inches of rain to fall in a SW to Northeast orientation with above average confidence. This part of the nation will be sensitive to additional rainfall, let alone a large area with several inches of new accumulations. The Moderate Risk area for excessive rainfall remained in effect from northeast Arkansas to western Ohio with the Slight Risk area stretches from the Arkansas/Louisiana border to western Pennsylvania. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5cL67REnXzswg1dnoRFHcGzLCw4sQAQmmaUw0ZYxqRAC= h7yyVNzlbSjbkbYprJEcfvwcc4h3WiRHxPONaMrOtg3Ef_g$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5cL67REnXzswg1dnoRFHcGzLCw4sQAQmmaUw0ZYxqRAC= h7yyVNzlbSjbkbYprJEcfvwcc4h3WiRHxPONaMrOABFmqBM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5cL67REnXzswg1dnoRFHcGzLCw4sQAQmmaUw0ZYxqRAC= h7yyVNzlbSjbkbYprJEcfvwcc4h3WiRHxPONaMrOx4uooaA$=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) .