Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Mar 22 2023 20:30:47 FOUS30 KWBC 222030 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 PM EDT Wed Mar 22 2023 Day 1 Valid 16Z Wed Mar 22 2023 - 12Z Thu Mar 23 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHERN CALIFORNIA AND CENTRAL ARIZONA... Maintained the on-going Marginal Risk area for portions of southern California and central Arizona. Additional rainfall is expected on and off throughout the day and into the evening across this area as an upper low initially along the central California coast fills and the lingering trough axis with cold temps aloft tracks into the Desert Southwest later tonight. The latest HRRR and ARW both generate upwards of 500 J per kg of surface-based CAPE during the afternoon as low/mid level lapse rates steepen while moisture continues to be transported inland by west to southwest flow at 15 to 30 kts. Additional rainfall of an inch or so (mainly focused in/near the terrain) will be falling on areas that are already hydrologically sensitive to additional precipitation.=20 Bann 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!4tFf7ln1a1ooiH9V6py-WQtptnjieNzc_6cn3UiVZ9Gu= 27c3gv4r1NfhbewUSWZ15RF4T1Q90qlL8g66ZzKUoPoLB5g$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4tFf7ln1a1ooiH9V6py-WQtptnjieNzc_6cn3UiVZ9Gu= 27c3gv4r1NfhbewUSWZ15RF4T1Q90qlL8g66ZzKUY13yF3A$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4tFf7ln1a1ooiH9V6py-WQtptnjieNzc_6cn3UiVZ9Gu= 27c3gv4r1NfhbewUSWZ15RF4T1Q90qlL8g66ZzKUhjhzmVs$=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. 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