Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Dec 20 2022 07:44:28 FOUS30 KWBC 200744 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 243 AM EST Tue Dec 20 2022 Day 1 Valid 12Z Tue Dec 20 2022 - 12Z Wed Dec 21 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF FLORIDA & THE SOUTHEAST COAST... Florida Peninsula... Divergence aloft will be sponsored by the right entrance region of an upper level jet over the Southeast U.S. and difluence over the Florida peninsula and the northeast Gulf of Mexico. A blossoming area of showers and thunderstorms over the eastern Gulf of Mexico will make its way inland on Tuesday and Tuesday night/early Wednesday morning. Precipitable water values of 1.25-1.75" are expected within an increasingly saturated atmosphere. Overlapping low- to mid-level frontogenesis combined with 500-1000 J/kg of MUCAPE is expected to foster heavy rainfall, which could be as much as 2" in an hour where cells train/thunderstorm activity organizes. Various pieces of deterministic guidance show the potential for local amounts in the 2-5" range, mostly across the central and southern FL peninsula. Portions of central and southern FL have received 300-600% of their average rainfall during the=20 past week, but since this is their dry season, this amounts to spotty 2-4", which in the warm season would be an average day.=20 The Marginal Risk has been maintained for this area, with the biggest potential impacts in urban areas. Georgia and South Carolina coast... The guidance continues to show a signal for potential heavy rainfall near or just offshore the coast of GA and SC. This occurs to the north of a surface low which slowly spins up in place offshore eastern FL before eventually heading out to sea once a fast moving shortwave along the Gulf Coast escorts it away from the region. Overlapping low- to mid-level frontogenesis should aid heavy rainfall production. Model guidance showing the potential for 2-5" amounts near to just offshore as their mass fields show just enough dispersion in the low levels/near 850 hPa and instability fields to open to the door to more ashore solutions. Instability is expected to rise to 250-1000 J/kg near to just offshore, in the vicinity to the Gulf Stream, with precipitable water values also following suit, rising to 1-1.25" within an an environment with 1000-500 hPa thickness values in the low to mid 550s decameters, implying nearly complete saturation.=20 With the guidance showing heavy rainfall so close to the coast, reintroduced a Marginal Risk area in this region as a precaution.=20 Coastal lows with this sort of evolution have been known to produce heavy rainfall in this region in the past. Hourly rain totals to 1.5" should be possible within this sort of environment. As this is a marshy area for the most part, any issues -- should the heavy rainfall make it ashore -- would be confined to the urban areas within the Marginal Risk's bounds. =20=20 Roth 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!7zrDHT0K-veef9j-2qxKDX9WoMzv5K1TdqHoG80l8dbI= WeQcDzB_KnTWyeymie_BrspundMCFaisloCOa_BpBDCn17M$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7zrDHT0K-veef9j-2qxKDX9WoMzv5K1TdqHoG80l8dbI= WeQcDzB_KnTWyeymie_BrspundMCFaisloCOa_BpLQ2ua3M$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7zrDHT0K-veef9j-2qxKDX9WoMzv5K1TdqHoG80l8dbI= WeQcDzB_KnTWyeymie_BrspundMCFaisloCOa_BpTU0yN6g$=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) .