Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Feb 12 2024 20:22:22 FOUS30 KWBC 122022 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 317 PM EST Mon Feb 12 2024 Day 1 Valid 16Z Mon Feb 12 2024 - 12Z Tue Feb 13 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHEAST U.S....=20 16Z Update: Deep convection continues this morning across portions of southern/southeast Alabama through southern Georgia and parts of the Florida Panhandle along a frontal boundary draped in the area. A plume of deeper moisture, characterized by PWs in excess of 1.5" along with an axis of instability (upwards of 500 J/kg along the coast). A favorable setup for training/repeating thunderstorms will continue through this afternoon, moving eastward across portions of southern Georgia where hourly rainfall totals between 1-2" will be possible (12Z HREF neighborhood probabilities for 1" in 1-hr peak near 50 percent) and localized 2-3" totals will be possible through the rest of the afternoon. The 12Z hi-res guidance has shown a southward shift compared to the previous forecast cycles with the best potential for heavy rainfall from far southeast Alabama through central South Carolina. Further north across northern Georgia, upstate South Carolina, and western North Carolina, the guidance has trended lighter and without any deep instability, higher rain rates will be harder to find. A dry slot may also limit the overall rainfall totals and coverage as well. Meanwhile, as the upper low moves from the Tennessee Valley through the Central Appalachians, a secondary stripe of heavier QPF is likely to set up from portions of Kentucky through West Virginia and portions of Maryland. Thermal profiles are more in question but precipitation is likely to start off as heavy rain before colder air wraps in and dynamic cooling takes over. The 12Z hi-res guidance has trended higher with a stripe of 1" to locally 2" of rainfall in a relatively short time period, which over these areas may be enough to cause some minor flooding issues. As a result the Marginal Risk was expanded northward across portions of the Ohio Valley and Central Appalachians. Taylor ---previous discussion--- There is a continuing threat of excessive rainfall on Monday from Alabama into the Carolinas as secondary cyclogenesis begins under the base of the cold air damming while the initial cyclone fades as it moves into WV on the west side of the cold air dam. Warm air advection east of the incoming cold front brings instability up to an outflow boundary/possible segment of the polar front and leads to heavy rainfall over saturated/saturating ground across portions of AL and GA before shifting east-northeast with time.=20 Precipitable water values increase to values at or slightly above 1.75", and MU CAPE of 500-1500 J/kg resides near and south of the boundary. Low-level inflow/effective bulk shear should be more than sufficient for organized convection, both in training bands and possible mesocyclones. Low- to mid-level frontogenesis will aid the heavy rain threat as well. Hourly rain totals up to 2" are possible, particularly early on across portions of SC and GA.=20 Local amounts of 5" are possible. The threat areas are based on presumptions of what the soil saturation could look like at 12z along with where the heaviest rain is expected to fall, so there is more than the usual uncertainty in the flash flood/excessive rainfall threat across eastern GA, SC, and vicinity. Threat areas have been expanded westward through western GA and AL from continuity to account for the above. Areas across the Carolinas and southern VA show better continuity. Roth Day 2 Valid 12Z Tue Feb 13 2024 - 12Z Wed Feb 14 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 Dolan 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!4tIFIv-Ly_4psxHXDaKTXx8K1x1T_L-4wFGp2I0N_HBN= AOZ1iaEIkJfG4zn9ZUPYSajoIPKDDgR0BX4_yb4vLqybBs4$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4tIFIv-Ly_4psxHXDaKTXx8K1x1T_L-4wFGp2I0N_HBN= AOZ1iaEIkJfG4zn9ZUPYSajoIPKDDgR0BX4_yb4vNW8yJbE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4tIFIv-Ly_4psxHXDaKTXx8K1x1T_L-4wFGp2I0N_HBN= AOZ1iaEIkJfG4zn9ZUPYSajoIPKDDgR0BX4_yb4vKJRDkz4$=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) .