Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 29 2023 08:28:26 FOUS30 KWBC 290828 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 427 AM EDT Fri Sep 29 2023 Day 1 Valid 12Z Fri Sep 29 2023 - 12Z Sat Sep 30 2023 ....A MODERATE RISK OF EXCESSIVE RAINFALL IS IN EFFECT OVER PORTIONS OF THE NORTHEAST... ....Mid-Atlantic into Northeast... An upper-level trough will support the amplification of an inverted surface trough and low pressure system off the Mid-Atlantic/Northeast Coasts today. There will be thunderstorms with heavy rainfall and serious flash flooding concerns over parts of the northern Mid-Atlantic and Northeast. Rounds of showers and thunderstorms, which began overnight, will continue and pickup in intensity through the morning rush hour. Some of the 00z hi-res guidance didn't capture the 01z-02z storms that moved into the New York Metro so there is a concern that this under performance may continue into the day 1 period. This antecedent rainfall has also primed surfaces for runoff of subsequent rainfall. A favorable low level jet, shallow instability and substantial surface frontogenesis will combine to produce efficient rainfall rates on the order of 0.25-0.5"/hr from northeastern New Jersey to coastal Connecticut where a Moderate Risk of Flash Flooding is in effect. Anywhere from 2-6" of rainfall are expected to accumulate by later this evening when the greatest threat of flash flooding will subside. Areas that are prone to flash flooding across the New York Metro Area will likely experience flash flooding today, so turn around don't drown! ....Upper Midwest/Great Lakes... Shortwave energy propagating south-north into Canada will drive showers and scattered to isolated thunderstorm activity over the Upper Midwest today. Another inverted surface trough will direct and enhance anomalous moisture plume with PWATs of 1-2" into much of Minnesota and northwestern Wisconsin. Rainfall totals of 1-2 inches are possible over portions the Upper Midwest by tomorrow morning. ....Florida... The back end of a slow moving cold front will act as a focus for scattered to isolated showers and thunderstorms today. A Marginal Risk area was continued to account for any localized flash flooding concerns that may arise. Kebede Day 2 Valid 12Z Fri Sep 29 2023 - 12Z Sat Sep 30 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE GREAT BASIN AND FLORIDA... ....Great Basin/Nevada... A deep upper-trough will transport a modest plume of moisture into the West on Saturday. A cold front associated with a deepening low pressure system will act as a focus for convection over the Great Basin in particular. Some parts of central Nevada, southeastern Oregon and southwestern Idaho could see rainfall rates in excess of 0.25"/hr. Ample forcing over elevated terrain could lead to more efficient/enhanced rainfall. Between 0.5-1" total areal rainfall is forecast over 3-4 hour period therefore, localized flash flooding is our primary concern. ....New Mexico/west Texas... Convection supported by an upper trough to the West and shortwave energy downstream from it will support another localized flash flood threat over parts of eastern New Mexico and into west Texas. Decent instability, modest moisture flux and low level jet may produce bursts of heavy rainfall over our marginal risk area. Urban areas and dry washes are most vulnerable of flash flooding. ....Florida... A slow moving shortwave trough will allow for the continuation of scattered to isolated thunderstorms across the central/southern peninsula on Saturday. Some cells may produce localized heavy rainfall within the marginal risk area. Antecedent conditions will also contribute to the sensitivity to any isolated heavy rainfall threats. Kebede 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!7OxLHg03rKHnC_yg57Dvm--RpRRE6AYihQ9kAc1HH9bh= gTbOKWBElbEdSRMuKfaL09K61oPAunOzY0_9qngn0tFAtq8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7OxLHg03rKHnC_yg57Dvm--RpRRE6AYihQ9kAc1HH9bh= gTbOKWBElbEdSRMuKfaL09K61oPAunOzY0_9qngn6O4fCKk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7OxLHg03rKHnC_yg57Dvm--RpRRE6AYihQ9kAc1HH9bh= gTbOKWBElbEdSRMuKfaL09K61oPAunOzY0_9qngnnIxuf6c$=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) .