Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat May 18 2024 07:49:43 FOUS30 KWBC 180749 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 349 AM EDT Sat May 18 2024 Day 1 Valid 12Z Sat May 18 2024 - 12Z Sun May 19 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST/CENTRAL GULF COAST... ....Southern Alabama/Georgia into the Florida Panhandle... Mid-level trough/weak closed low over the Lower MS Valley/Mid- South this morning will continue eastward across southern TN today=20 and into the southern Appalachians by early Sunday. On its=20 southeast side, a stream of mid- level impulses will move across=20 the FL Panhandle and southern AL/GA today ahead of a cold front=20 that will finally clear through the area by tomorrow. SW flow out=20 of the Gulf will maintain relatively high precipitable water values (~1.75" or +1.5-2 sigma) into the region ahead of the trough and=20 surface front, with more impressive 850-700mb moisture flux=20 anomalies into the region (+3 to +4 sigma). With ongoing convection over southern LA moving eastward, expect this to continue past 12Z along the I-10 corridor from southern MS eastward through early=20 afternoon. Thereafter, models suggest a loss of mid-level vorticity dynamics to sustain heavier rainfall but this may be underdone=20 given the approach of the cold front with still sufficient moisture available. Slight Risk outline was generally constrained to the=20 higher probabilities of >2" QPF in the 12-18Z period this morning.=20 Broader Marginal Risk covers much of the rest of the Southeast into the Carolinas where isolated heavier rain rates are possible.=20 Trimmed away the northern/northeastern side of the Marginal Risk=20 where instability is low (or non-existent) on easterly flow. Fracasso Day 2 Valid 12Z Sun May 19 2024 - 12Z Mon May 20 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20 THE CENTRAL PLAINS/CORN BELT... Broad SW flow over the central Plains across the Corn Belt will=20 bring in increasing moisture to the region on Sunday with a surface frontal boundary hung up over Iowa. Mid-level vorticity will exit=20 the central Rockies and moves across the central Plains as=20 precipitable water values rise to around 1.50" (+1.5-2 sigma) with=20 some instability in the afternoon/early evening (500-2000J/kg) that could yield some 1"/hr rates (per 00Z HREF thru 00Z Mon) which are near FFG values over Iowa and nearby areas. The region has been=20 fairly dry the past week (most of the region has had about 50% of=20 the normal rainfall) so much of the rain will be beneficial, but=20 given 1-hr FFG values near 1"/hr (between MCI-OMA- DSM), maintained the Marginal Risk outline for the region. Higher probabilities=20 exist farther southwest into central Kansas (to where the Marginal=20 was extended), but FFG values are higher as well (2"/hr). 12Z CAM=20 guidance through 12Z Mon may shed a little more light on the higher rainfall potential over the entire 24 hours. Fracasso Day 3 Valid 12Z Mon May 20 2024 - 12Z Tue May 21 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20 THE CENTRAL PLAINS/CORN BELT... Upper pattern remains fairly similar to D2 across the Plains, with broad SW flow over the region. One wave will exit through the=20 Upper Midwest as troughing over the West deepens via northern and=20 incoming southern stream vorticity. Upper diffluence east of the=20 Rockies will support widespread showers/storms over the central=20 Plains Monday into Monday night along the stalled surface boundary, with sufficient moisture in place and sfc CAPE 500-1500J/kg.=20 Heaviest rainfall per the ensembles lie over western Nebraska (Sand Hills) where FFG values are highest, so focused the area to the=20 southeast and east into Iowa where rainfall on D2 may lower FFG=20 values a bit (from already somewhat lower numbers).=20 Fracasso Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4Q8kMzAMOBlP1fOcR2CnxMXqa0VwPfKQctqQznDfSUHg= ABPnV4rldM5Q1KwtSdYZ1bsNyNMU9r6YcJaVfuQf9R5AANY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4Q8kMzAMOBlP1fOcR2CnxMXqa0VwPfKQctqQznDfSUHg= ABPnV4rldM5Q1KwtSdYZ1bsNyNMU9r6YcJaVfuQf9CgYBmQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4Q8kMzAMOBlP1fOcR2CnxMXqa0VwPfKQctqQznDfSUHg= ABPnV4rldM5Q1KwtSdYZ1bsNyNMU9r6YcJaVfuQfwYMsSWs$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .