Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jan 20 2023 00:48:42 FOUS30 KWBC 200048 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 747 PM EST Thu Jan 19 2023 Day 1 Valid 01Z Fri Jan 20 2023 - 12Z Fri Jan 20 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 Hurley Day 2 Valid 12Z Fri Jan 20 2023 - 12Z Sat Jan 21 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 Chenard Day 3 Valid 12Z Sat Jan 21 2023 - 12Z Sun Jan 22 2023 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE GULF COAST & SOUTHEAST... 20z Update: Not much to add from what was described below. Forecast still looks on track with a Marginal flash flood risk over the Southeast. Better instability and higher rain rates still look confined to coastal areas...but with strong IVT anomalies, low/mid level frontogenesis and upper level divergence over inland areas, would still expect the potential of embedded higher totals away from the coast. Plus while 3hr FFG is around 4" over coastal areas, it is closer to 2-2.5" further inland...so in balancing expected rainfall rates/totals with this FFG, it makes sense to just maintain the broad Marginal risk at this time. Thus, while some thought was given to shrinking the Marginal risk to only include areas closer to the coast, we opted to maintain continuity for now and will continue to monitor trends. Chenard ....Previous Discussion... An upper low moving into the southern High Plains is expected to phase with a northern stream trough in the Northern Plains and progress eastward into the Mississippi Valley by Sunday morning.=20 This feature will aid divergence aloft across portions of the Gulf Coast and Southeast. Ahead of its associated cold front, precipitable water values rise to 1.25-1.75", which is high for late January. Any surface based CAPE is expected to be close to the Gulf Coast. However, MU CAPE of up to 500 J/kg should sneak somewhat inland across areas of the eastern Gulf coast.=20 Compensating for the minimal CAPE intrusion from the Gulf of Mexico is overlapping low- to mid-level frontogenesis which should aid precipitation production from central MS eastward into central GA Saturday night into Sunday morning. Hourly rain totals to 2" along the Gulf Coast and 1" across the Interior Southeast appear the most probable at this junction. Inflow at 850 hPa is fairly strong -- approaching 50 kts -- and broadly cyclonic, so that progressive nature of the upper trough and cold front may not have much impact on QPF magnitude along and ahead of the long warm front. In the presence of enough instability, convection should attempt to organize The guidance generally agrees on narrow swaths of 2-4". Precipitation over the past week has been generally below average. The region is in the process of getting some precipitation at the present time, though the expected totals in the very short term shouldn't change the soil saturation very much between now and then. Overall, feel the inherited Marginal Risk from experimental day 4 continuity seemed reasonable so let it ride for day 3 with minimal changes. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8Q1sDTdFy4n6TFW7c9xOKgXDzOJYvggRdr_hOPCSNVfp= 202GBAnTBCLP_lF53iTpnohjM4lqKipfQPe8yw5OTIbjpRA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8Q1sDTdFy4n6TFW7c9xOKgXDzOJYvggRdr_hOPCSNVfp= 202GBAnTBCLP_lF53iTpnohjM4lqKipfQPe8yw5O_o8ufvI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8Q1sDTdFy4n6TFW7c9xOKgXDzOJYvggRdr_hOPCSNVfp= 202GBAnTBCLP_lF53iTpnohjM4lqKipfQPe8yw5Ovq2iLHw$=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) .