Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Feb 12 2023 00:12:15 FOUS30 KWBC 120012 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 711 PM EST Sat Feb 11 2023 Day 1 Valid 01Z Sun Feb 12 2023 - 12Z Sun Feb 12 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR THE COASTAL SOUTHEAST... Moisture has overspread portions of the Southeast as the flow aloft backs in response to a closed mid- and upper-level low approaching from west. Recent indications show a new area of low pressure forming in southeast GA south of Waycross. Convection should grow in coverage and intensity across coastal GA, SC, and far southeast NC overnight as the new low pressure area travels just inland of the coast to near Charleston before possibly tracking just offshore NC. Instability is growing, with 500-1000 J/kg of MU CAPE near the new surface low, which should continue to exist in its vicinity as it moves northeast. Precipitable water values range from 1.5-1.75" where the heaviest rainfall is expected. Along with some overlapping low- to mid-level frontogenesis, the environment support locally efficient rainfall totals and potentially fall across areas that have received 100-200% of their average 7 day precipitation within the Slight Risk area. The greatest threat for 1-2"/hr rainfall totals is most likely from roughly Savannah GA through Charleston SC. A Training convection is possible as the flow is fairly unidirectional out of the southwest; any mesocyclone formation would add to the heavy rain potential. Elsewhere, ahead of the closed upper-level low, steady and slow-moving rainfall over portions of AL and GA could lead to some isolated runoff concerns. Roth Day 2 Valid 12Z Sun Feb 12 2023 - 12Z Mon Feb 13 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS 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. Present indications are that the higher rainfall rates should be confined close to the North Carolina 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. Precipitable water values near 1.5", which ranks just above the 90th climatological percentile (per the GEFS) along with 850 mb easterly winds of 40 knots should result in decent moisture transport into the region. So this limited area has the best chance for rainfall rates to be high enough for flooding concerns. 12Z HREF probabilities confine low-end neighborhood probabilities of 1 inch per hour rates to this area, which includes the Outer Banks, 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. This also includes parts of southeast Virginia, where rainfall rates will not be particularly impressive, but rainfall totals up to 2" could pose an urban runoff or flood risk. Snell 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. Snell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9Q83UhXztGWQtrmYMjA8V9MRTlBOAhf2BAPSLL36OG_B= ZssZpfPJi_hJyYSbtUCw3DVGkaqLeVadiUHsIZFsVGfmAIw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9Q83UhXztGWQtrmYMjA8V9MRTlBOAhf2BAPSLL36OG_B= ZssZpfPJi_hJyYSbtUCw3DVGkaqLeVadiUHsIZFscYq8dnU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9Q83UhXztGWQtrmYMjA8V9MRTlBOAhf2BAPSLL36OG_B= ZssZpfPJi_hJyYSbtUCw3DVGkaqLeVadiUHsIZFsD63HJ2k$=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) .