Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Sep 05 2023 07:57:54 FOUS30 KWBC 050757 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 357 AM EDT Tue Sep 05 2023 Day 1 Valid 12Z Tue Sep 05 2023 - 12Z Wed Sep 06 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN PLAINS AND UPPER MIDWEST AS WELL AS THE MID-MISSISSIPPI VALLEY INTO THE OZARKS... ....Upper Midwest... A vigorous shortwave over SD this morning will continue eastward into MN by early Wednesday with its attendant surface low and cold front out ahead of it. Precipitable water values over 1.50-1.75" (+1.5 to +2.5 sigma) will precede the front in the warm sector with dew points into the upper 50s to mid 60s, south of a boundary stretching into Ontario. To the southeast, a separate weakening shortwave over the mid-Mississippi Valley will lift into the Great Lakes bringing its own surge of moisture into the region. Afternoon convection is expected to increase over MN today where SPC highlights a Slight Risk of severe weather, with frontogenesis along the northern boundary acting to focus rainfall over northeastern MN/Arrowhead where 1-2" areal average rainfall is forecast, and local amounts of 3-4" possible. 00Z HREF neighborhood probabilities show low (<15%) chances of exceeding 1-hr FFG but a bit higher (15-30%) chances of exceeding 3-hr FFG values. The region has been very dry for the past 1-2 weeks, so with 1-hr rates generally 1-2"/hr at most, expect mainly isolated flash flooding where heavier rain falls over more sensitive areas. Maintained the Marginal Risk area into northern WI and into the U.P. of Michigan where rainfall will move into the region this evening into the overnight hours. Farther west, any rainfall just after 12Z over the central Dakotas may exceed recently depressed FFG values from overnight rainfall. ....Mid-Mississippi Valley/Ozarks... Marginal Risk area is outlined from eastern OK to the Mid-South, out ahead of a surface cold front approaching from the NW. Despite the exiting shortwave in the morning hours into the Great Lakes, southerly flow will supply sufficient moisture into the region with precipitable water values around 1.75 inches (+1 to +1.5 sigma). Instability will increase during the day and support isolated to scattered storms into the Ozarks where FFG values are relatively lower than surrounding areas and very isolated storms farther east where the models are struggling with the evolution. Fracasso 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!9Pcr0vguc6XDQES3ZQK06UJWjif3TJLT383kwlaOxbnK= HmO0DVd-KyxMxdD3uVyRBZ-UUui39hampS6s3qRIz05ffFs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9Pcr0vguc6XDQES3ZQK06UJWjif3TJLT383kwlaOxbnK= HmO0DVd-KyxMxdD3uVyRBZ-UUui39hampS6s3qRIhVsAo30$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9Pcr0vguc6XDQES3ZQK06UJWjif3TJLT383kwlaOxbnK= HmO0DVd-KyxMxdD3uVyRBZ-UUui39hampS6s3qRIJXiR70U$=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) .