Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 11 2023 07:25:44 FOUS30 KWBC 110725 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 324 AM EDT Fri Aug 11 2023 Day 1 Valid 12Z Fri Aug 11 2023 - 12Z Sat Aug 12 2023 ....THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL IN THE SOUTHEAST, OZARKS, CENTRAL GREAT LAKES, DESERT SOUTHWEST, AND CENTRAL SIERRA NEVADA... Zonal flow established across the country has set up a relatively quiet pattern for a couple days as the areas of deepest moisture across the southern US are temporarily separated from the greatest forcing across the northern US. This is not to say there won't be showers and thunderstorms in various areas, but the lack of connection between the moisture and the forcing should prevent them from organizing enough to cause higher-level flash flooding concerns. ....Michigan, Northern Indiana, Northwest Ohio... A 15-25 kt LLJ will transport a bit of moisture from the Midwest that will be lacking a connection with the Gulf into portions of the Midwest. Convection is likely to break out along this front, especially during peak heating, and continuing into the evening. CAMs guidance is in decent agreement that multiple rounds of showers with some embedded storms will form along the southern boundary between steadier rain and forcing to the north, and isolated convection with little forcing to the south. Thus, this region is likely to be in the middle, and thus subject to multiple rounds of storms. The southwesterly flow will also transport air with MUCAPE around 1,500 J/kg, and PWATs to around 1.5 inches. This is far from impressive for this time of year, but will be enough moisture availability for the storms. The inherited Marginal Risk was expanded to the northwest to align with the latest guidance trends, increasing rainfall amounts into the U.P. as well. ....Ozarks and Mid-Mississippi Valley into the Southeast... Unlike further north, this area will have plenty of moisture and instability, with PWATs exceeding 2 inches in some areas, and instability exceeding 4,000 J/kg of MUCAPE, which is extremely unstable. Thus, what will be missing in this area is a strong enough source of forcing to allow the storms that will form over this area to organize. Scattered storms are already over portions of northern AL this morning. They will track southeastward, following the greatest moisture and instability. However, other than localized outflow boundaries, the forcing will be limited. Thus, expect the storms to form and reform as the broader area of scattered storms moves southeastward, but the storms will be largely independent of each other. While the plentiful moisture and instability will support individual storms becoming strong enough to produce heavy rainfall, the storms will be moving enough and will be widely scattered enough that the flash flooding threat will be largely confined to urban and poor drainage areas. High FFGs common across the Deep South will also limit the flooding threat. ....Eastern Arizona and Western New Mexico... A very diffuse monsoonal signature is the best the guidance is showing as far as convective coverage goes this morning for the return of storms again this afternoon. With limited forcing and capping aloft, the convection may not be quite as strong today as they were yesterday evening. Nonetheless given the sensitivity of the area to flash flooding, particularly over burn scars, slot canyons, dry washes, and any urban areas, the Marginal Risk was maintained with this update. ....Central Sierras into Nevada... The guidance continues to indicate the potential for isolated flash flooding from the Central Sierra Nevada eastward into central NV. No significant changes were noted with this update, as any storms capable of flash flooding will only be able to form if there is enough break in the cloud cover to allow instability to increase. 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!9LPSs-Dws8UFfjtbETqCYD5dILRPf3q7WhMbS8ss-zSb= y1B-0eqCaNw-nePB78R0Qh43LuV5bGag7hokMhmZJaUzw0U$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9LPSs-Dws8UFfjtbETqCYD5dILRPf3q7WhMbS8ss-zSb= y1B-0eqCaNw-nePB78R0Qh43LuV5bGag7hokMhmZi2XTb2Y$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9LPSs-Dws8UFfjtbETqCYD5dILRPf3q7WhMbS8ss-zSb= y1B-0eqCaNw-nePB78R0Qh43LuV5bGag7hokMhmZCZoPuvA$=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) .