Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Dec 02 2023 08:26:05 FOUS30 KWBC 020825 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 325 AM EST Sat Dec 02 2023 Day 1 Valid 12Z Sat Dec 02 2023 - 12Z Sun Dec 03 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR THE FLORIDA PANHANDLE INTO LOWER SOUTHEAST ALABAMA... ....Gulf Coast and Southeast... A strong cold front pushing east out of the Plains and into the Southeast will draw deep Gulf moisture northeastward along and ahead of the front. Meanwhile, a strong southwesterly jet streak will continue intensifying from the southern Plains to the southern Appalachians. This will put the portions of the Gulf coast in the favorable right entrance region of the jet. Helping intensify the jet will be a strong shortwave that will also be tracking northeastward. While the shortwave is unlikely to have a direct impact on the storms, it's influence on the upper jet will help support broad scale lift over the area. Showers and thunderstorms are ongoing across LA and MS this morning. Heavy-rain-producing thunderstorms have been embedded within the broader rain shield, which fortunately have been moving enough to limit flooding impacts somewhat. Nonetheless their tendency to produce 3 inch per hour rainfall rates at times has resulted in localized flash flooding in portions of southwestern LA. Storms and the broader rain shield will push off to the east as more storms develop over the Gulf through the morning due to the aforementioned large scale environmental lift. The heaviest rain of the day and the greatest potential for flooding will likely be in the morning hours/first part of the day today. Supporting the storms are CAPE values between 500 and 1,000 J/kg over the Gulf and the immediate Gulf Coast. Instability generally diminishes as one goes further inland, but the increasing southwesterly flow supported by the jet is helping advect the unstable air mass further inland. There's likely to be a break in the significant rainfall for much of the afternoon through the evening hours between systems. A renewed round of storms is expected to develop overnight tonight into the early morning hours of Sunday. While the storms will have more support in the upper levels as the jet streak intensifies to over 150 kt, the time of day, faster storm motion, and lesser forcing across the FL Panhandle and nearby portions of AL/GA should limit both the storms' intensity and coverage tonight/early Sunday morning. The Slight and surrounding Marginal Risk areas are largely unchanged with this update. Given the above reasons, the Slight may be able to be cancelled with the midday update depending on the evolution of the convection at that time. ....Western Oregon into far Northwest California... The next in the long string of fronts associated with a persistent atmospheric river is already moving into the Pacific Northwest (primarily Washington State) this morning. The heaviest rain will shift southward and diminish through the morning. A stronger front will push into the far northern CA and OR coasts tonight, which is when the bulk of the day's rainfall is expected. Expect a soaking 3 to 5 inches of rain into the coastal ranges of OR and the Cascades through tonight, with local amounts approaching 8 inches by Sunday morning. The impulse of moisture will be accompanied by much warmer air typical of many atmospheric rivers. This will rapidly raise snow levels, allowing snowmelt to contribute some to rising river levels. Since the area has been relatively dry recently, much of the rainfall and snowmelt should be contained in the river banks, so only isolated flash flooding in particularly sensitive areas is expected through Sunday morning. The Marginal Risk was maintained with this update. Wegman 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!9sI4wBEAzWIYC1mSqIjj3Lr2uheizOIyj7966Nx43-Pk= H_Y1x5SWbYPeSe_IVrsT2QUiSspKioqY0tTXUgBFt518p6I$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9sI4wBEAzWIYC1mSqIjj3Lr2uheizOIyj7966Nx43-Pk= H_Y1x5SWbYPeSe_IVrsT2QUiSspKioqY0tTXUgBFAwwWNb4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9sI4wBEAzWIYC1mSqIjj3Lr2uheizOIyj7966Nx43-Pk= H_Y1x5SWbYPeSe_IVrsT2QUiSspKioqY0tTXUgBFt_z-FLU$=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) .