Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Mar 12 2023 08:25:28 FOUS30 KWBC 120825 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 424 AM EDT Sun Mar 12 2023 Day 1 Valid 12Z Sun Mar 12 2023 - 12Z Mon Mar 13 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF NORTHERN CALIFORNIA AND EXTREME SOUTHWESTERN OREGON... ....California... The much-advertised next atmospheric river will be ramping up during the day as a deep positively tilted trough approaches the coast of the Pacific Northwest later tonight. Deep unidirectional west southwestly flow ahead of the troguh will continue draw plenty of moisture into northern California...with precipitable water values around 0.75 inches remaining consistent through the period. This flow will favor upsloping not just along the coast, but right up into the northern end of the Sacramento Valley as well. Meanwhile, snow levels will be largely steady in this region, holding between 5,500 and 6,500 ft. This is plenty high enough to result in rainfall on all but the highest peaks of the mountains in Siskiyou County. Continued snowmelt will also contribute to rising river levels and the excessive rainfall potential. The primary changes to the previous outlook was a sbtle southward extension of the Slight Risk area along the coast. Rainfall rates of 0.25-0.5 inches/hour are expected...with 2 to potentially 3 inches of rainfall in most of the higher elevations, with 1/2 to 1 inch expected in the middle of the valley. Changes made to the Marginal Risk on Saturday area still looked reasonable with spaghetti plots of QPF still supporting the potential for an inch or more of liquid precipitation over an area with snow pack. As mentioned prviously...the farther north you go, the less time snow levels will be that high, but nonetheless those rainfall amounts on snow could result in isolated flooding issues, particularly in urbanized areas and around burn scars. ....Southern AL/GA... There is a Marginal Risk of excessive rainfall over portions of southern Alabama and Georgia where the latest guidance has finally come into better agreement with the placement of the heaviest rainfall...presumably being focused on remnants of overnight convection and subsquen redevelopment. Corfidi vectors are close to parallel to the axis of the stalling front, and guidance is slowly catching on to this. Despite increasing QPF in the area...the Flash Flood Guidance is high so biggest concern is where cells with the highest rainfall rates train or in areas of repeat convection. Bann Day 2 The Day 2 outlook will be updated by 0830Z. 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!9COGSXtPpofP1Pjn5SJQP0rOOICOtR9C9rqe4ZuqKZeC= gM67V_zswDbdbmXjsYyJqNxQBXGiXTOECD-wckEJiNO9Gko$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9COGSXtPpofP1Pjn5SJQP0rOOICOtR9C9rqe4ZuqKZeC= gM67V_zswDbdbmXjsYyJqNxQBXGiXTOECD-wckEJbZ1cMvA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9COGSXtPpofP1Pjn5SJQP0rOOICOtR9C9rqe4ZuqKZeC= gM67V_zswDbdbmXjsYyJqNxQBXGiXTOECD-wckEJmOt_X4Y$=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) .