Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Dec 07 2024 08:20:25 FOUS30 KWBC 070820 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 320 AM EST Sat Dec 7 2024 Day 1 Valid 12Z Sat Dec 07 2024 - 12Z Sun Dec 08 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill Day 2 Valid 12Z Sun Dec 08 2024 - 12Z Mon Dec 09 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20 THE CENTRAL GULF COAST... The Slight Risk has been maintained along and near the central=20 Gulf Coast for Sunday and Sunday night, confined to where more=20 appreciable deep-layer instability exists to support a higher=20 probability of more intense short-term rainfall rates (2"+/hr). Still, this is considered a lower-end Slight Risk (based on the wide 15-40% probability spectrum), suggesting widely scattered=20 instances of flash flooding at best (given expected localized=20 totals of 2-4" are near the corresponding 3-hr FFGs of 3-4").=20 Also, much of the Slight Risk area, particularly from Jasper TX=20 east-northeast to Alexandria LA, have received heavy rainfall over recent days, and as a result the antecedent soil conditions and=20 streamflows are a bit higher compared to areas farther north (where NASA SPoRT-LIS 0-100 cm soil moisture in the bottom 10th percentile for much of MS/AR/LA). In addition to drier antecedent conditions=20 farther north and east across the Mid-South, very limited elevated instability (MU CAPE ~200 J/kg at best) should prevent rainfall=20 rates from climbing too high (generally 1.5"/hr or less, driven by=20 impressive forcing via the shortwave and associated jet dynamics).=20 This suggests that a Marginal Risk should suffice with any flash=20 flooding being highly localized, despite areal average rainfall=20 amounts near 2" (expected to be spread out over 6+ hours). Churchill/Hurley Day 3 Valid 12Z Mon Dec 09 2024 - 12Z Tue Dec 10 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE=20 CENTRAL GULF COAST... The shortwave trough responsible for heavy rainfall on Sunday over much of the Lower MS Valley looks to eject northeastward into the central Appalachians and Mid-Atlantic on Monday, bringing largely=20 beneficial rainfall (with totals generally under 1") to much of the Northeast. Farther south along the central Gulf Coast, there are=20 hints of another (weaker) shortwave trough within the southern=20 stream that may enhance heavy rainfall along a trailing cold front. Given the slowing of the front, the opportunity for training areas of heavy rainfall will be greater on Day 3, best depicted by the=20 00z ECMWF and ECENS (depicting localized banded totals of 2-5" and=20 probabilities for 2" exceedance as high as 30%). This risk appears=20 greatest from southeast LA to southern AL and the tip of the FL=20 Panhandle, though the EC model system is the most extreme and=20 farthest east of all the models. Maintained the inherited Slight=20 Risk area with some adjustments, limiting the eastern extent a bit=20 given the lack of agreement from the other models. Uncertainty is=20 still relatively high, but subsequent outlooks should get a better=20 handle on things as these details begin to enter the CAM period. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4Tiok_HHEVDtBCD0ARPNEIePbXrOt9rXa6K5qcGSORMD= WZR6i6seXFFbEXM8t3tfGl8xdso4DH5kl2K54IBjhqpkS5o$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4Tiok_HHEVDtBCD0ARPNEIePbXrOt9rXa6K5qcGSORMD= WZR6i6seXFFbEXM8t3tfGl8xdso4DH5kl2K54IBjusUbWkU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4Tiok_HHEVDtBCD0ARPNEIePbXrOt9rXa6K5qcGSORMD= WZR6i6seXFFbEXM8t3tfGl8xdso4DH5kl2K54IBjb60vDRg$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .