Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Feb 11 2023 08:29:32 FOUS30 KWBC 110829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 328 AM EST Sat Feb 11 2023 Day 1 Valid 12Z Sat Feb 11 2023 - 12Z Sun Feb 12 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FROM THE EASTERN FLORIDA PANHANDLE THROUGH SOUTHERN SOUTH CAROLINA... The potential for heavy to possibly excessive rainfall will be focused along and near a quasi-stationary boundary draped over portions of the Southeast U.S. as the flow aloft backs in response to a closed mid- and upper-level low approaching from the southwest. Precipitation grows in coverage and intensity today as low pressure forms along the front...with an additional 1-3 inches of rainfall possible from the Florida Panhandle to southeastern North Carolina. Instability remains at a premium...but the forcing aloft from a coupled jet structure aloft and the focus provided by a surface cold front that sweeps across the area later today and this evening and encounters an atmosphere with precipitable water values ranging from 1.4 to 1.75 inches. This should be enough to support locally heavy rainfall rates and could overlap with areas that received locally heavy rainfall on Friday. Even if rainfall amounts are not as great as they were on Friday...the antecedent conditions warranted maintaining the Marginal and Slight Risk areas without too many changes. The fact that the front should keep the convection progressive will help to mitigate the flash flooding risk somewhat. Bann Day 2 Valid 12Z Sun Feb 12 2023 - 12Z Mon Feb 13 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR A SMALL PORTION OF FAR SOUTHEASTERN VIRGINIA INTO EASTERN NORTH CAROLINA... Rain will continue to spread northward and eastward at the start of the Day 2 period on Sunday morning as a mid- and upper-level low tracks across portions of the Southeast U.S.. Present indications are that the higher rainfall rates should be confined close to the coast where the upper level support from a coupled jet structure is initially in place followed by increasingly difluent flow to the north and east of the approaching upper low.=20 Both the ECMWF and GFS show 1.5 to 1.75 inch precipitable water values will be in place at 12Z Sunday with 850 mb easterly winds of 40 knots resulting in decent moisture transport into the region...so it appears this limited area has the best chance for rainfall rates to be high enough for problems. 00Z HREF probabilities confine low-end neighborhood probabilities of 1 inch per hour rates or 2 inch per 3 hour rates to this area through roughly 18Z before shifting out to sea. In reality...any heavy rainfall will be falling into coastal swamp and sandy soils, which are unlikely to respond with much flash flooding although urbanized areas are more likely to see isolated flash flooding. Bann Day 3 Valid 12Z Mon Feb 13 2023 - 12Z Tue Feb 14 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7XEIlygK191sJahGiip_EZMlV-oJ1mVhNSVyVW15b6em= qVCkCE_NcOvoD7-CyWqODM1Z7lsuTcIoMBizj7LB_YRqXVw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7XEIlygK191sJahGiip_EZMlV-oJ1mVhNSVyVW15b6em= qVCkCE_NcOvoD7-CyWqODM1Z7lsuTcIoMBizj7LBXNC4WvU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7XEIlygK191sJahGiip_EZMlV-oJ1mVhNSVyVW15b6em= qVCkCE_NcOvoD7-CyWqODM1Z7lsuTcIoMBizj7LBldNwcho$=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) .