Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Aug 27 2023 20:22:22 FOUS30 KWBC 272022 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 421 PM EDT Sun Aug 27 2023 Day 1 Valid 16Z Sun Aug 27 2023 - 12Z Mon Aug 28 2023 ....A SLIGHT RISK OF EXCESSIVE RAINFALL IS IN EFFECT FOR PORTIONS OF THE SOUTHEAST... ....Parts of the Southeast into the Lower Mid-Atlantic Region... Synoptic setup remains favorable across the Carolinas into southern Virginia down into northeast Georgia. Enhancement of an upper jet over the northern Mid-Atlantic and Northeast will provide increasing ascent across the area mentioned above. Anomalously moist environment centered over the Carolinas provides a footprint for enhanced rainfall risks, especially located along a stalled frontal boundary bisecting eastern NC down through central SC and GA. MLCAPE breaching 2500 J/kg will be common across much of the Lower Mid-Atlantic and Southeast US providing one of the last key ingredients to the setup. 12Z HREF still focusing heaviest QPF across much of eastern NC down into northeast SC with local maxima approaching 5+" this afternoon with evening activity farther west along the central NC/SC border. Locally significant flash flooding is still a possibility and the Slight Risk is maintained for 16Z. ....Tennessee and Kentucky... MCV is drifting east along the TN/KY border. Despite recent downward trends in multi-cell activity (rain rates decreasing and warming cloud tops) right around this low, there is sufficient instability (1000-2000 J/kg) and robust moisture (PWs 2 to 2.2") available. Given the potential for redevelopment, the Slight Risk was adjusted to along and ahead of the MCV including an eastward extension over northern TN. Also given the leading line developing over south-central KY, the Marginal Risk was expanded north. Will continue monitoring this focused area for development as it shifts farther east this afternoon. ....Rockies and High Plains... Scattered convection is anticipated across the Rockies down into the southern high plains of Texas this afternoon incorporated along an axis of elevated theta-e on the eastern flank of a western mid-level ridge. Marginal instability on the order of 500-1000 J/kg with greater instability over west Texas will aid in diurnally driven convection beginning after 18z. NWly flow will help propagate convection towards the south and east across the Front Range of CO down through eastern NM and the Caprock of TX. Locally heavy rainfall will allow for a chance of flash flooding, especially within any larger towns or cities where local FFG's are generally lower.=20 Kleebauer/Jackson Day 2 Valid 12Z Mon Aug 28 2023 - 12Z Tue Aug 29 2023 ....A SLIGHT RISK OF EXCESSIVE RAINFALL IS IN EFFECT FOR PORTIONS OF THE SOUTHEAST AND SOUTHERN MID-ATLANTIC... ....Southeast U.S into Southern Mid-Atlantic... Stalled frontal boundary across the southeast U.S will again be the focal point for a corridor of heavy rainfall during peak diurnal convection on Monday afternoon and evening. The corridor of higher theta-e located along the boundary and weak steering flow will provide an axis for rainfall rates exceeding 2-3"/hr in the heaviest cells. 12Z HREF CAM consensus is for two general areas of precip maxima; the southern Appalachians to Upland portions of South Carolina down through northern Georgia, and southeast Virginia and northeast North Carolina. Given the frontal boundary between the two with the aforementioned axis of moisture as well as Day 1 activity throughout, thought it prudent to expand the Slight Risk through Hampton Roads. The frontal zone continues southwest to the central Gulf Coast where similar heavy rain is anticipated, but given the typical higher flash flood guidance of the Deep South, maintained the Marginal Risk for southern AL/MS/southeast LA. ....Florida Peninsula... Constricted the Marginal Risk area to parts of west and southwest Florida peninsula coast as 12Z consensus for leading/outer bands of Idalia Monday night is generally limited to this more sensitive urban corridor from Tampa Bay through Naples. Monday afternoon activity across the rest of the southern peninsula as tropical moisture ahead of Idalia spreads north will need to be monitored, but as of now any excessive rain concern is rather isolated given the recent generally dry weather and high flash flood guidance. ....Colorado through West Texas.... Diurnally driven convective development downstream of a strong ridge axis is anticipated Monday afternoon into the overnight across the Colorado and New Mexico Rockies and onto the central/southern high plains, as well as west Texas. Flow aloft increases as it veers a bit from NWly to NNWly on approach of the eastward ridge axis which will help focus activity closer to the eastern slopes of the southern Rockies than activity this afternoon/tonight. A localized Slight Risk may be warranted should a focus area on Monday repeat over areas of heavy rain through tonight. Otherwise, a localized excessive rain risk is anticipated given the PW anomaly is near +1.5 sigma. Jackson Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4EUSZIzCv3otI7SryN08tuVJ7C1WD4WMz7hrF2No9gNX= Hsw4-jalVY8B1njXx5XiWCyUEdNvJiRnW0fTTbXUy984EG0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4EUSZIzCv3otI7SryN08tuVJ7C1WD4WMz7hrF2No9gNX= Hsw4-jalVY8B1njXx5XiWCyUEdNvJiRnW0fTTbXUMUi5vLI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4EUSZIzCv3otI7SryN08tuVJ7C1WD4WMz7hrF2No9gNX= Hsw4-jalVY8B1njXx5XiWCyUEdNvJiRnW0fTTbXUfPdhS14$=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) .