Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Feb 15 2025 00:03:37 FOUS30 KWBC 150003 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 703 PM EST Fri Feb 14 2025 Day 1 Valid 01Z Sat Feb 15 2025 - 12Z Sat Feb 15 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID-SOUTH... Models continue to show ingredients coming together late in the period to support developing heavy rain that will evolve into a=20 much larger threat on Saturday. Deepening moisture coincident with=20 a southwesterly 50 kt low level jet, interacting with an incoming upper level trough, is expected to support broader showers and=20 thunderstorm development across the region with time. MU CAPE of=20 500-1500 J/kg lies near the Arklatex, with several hour trends=20 showing a quick north- northeast advance of the instability=20 towards AR. There is some signal in the hi-res models showing=20 storms beginning to train later tonight, raising an increasing=20 threat for heavy accumulations near the end of the period, though=20 at the moment the signal is highest in 1"+ amounts through 12z.=20 Despite this, recent radar trends show hourly rain totals rising=20 into the 0.5-1" range in northwest LA, so the guidance could be=20 underperforming. Given the effective bulk shear, precipitable water values rising towards 1.5", and invading instability, mesocyclones are possible within this environment with time, especially late=20 tonight/Saturday morning. With the continued signal in some of the=20 guidance for training storms with locally heavy amounts beginning=20 to develop, hourly rain totals to 1.5" and local amounts to 3" appear to be the high bar, which would threaten areas with lower flash flood guidance values, particularly in and near western TN.=20 The Marginal Risk remains in place across portions of the region.=20 An eastward shift was made based partially on radar reflectivity=20 trends and the 18z HREF 0.5"+ in an hour probabilities. Roth Day 2 Valid 12Z Sat Feb 15 2025 - 12Z Sun Feb 16 2025 ....THERE IS A HIGH RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE TENNESSEE AND OHIO VALLEYS... ....Ohio and Tennessee Valleys... Confidence of a very impactful, life-threatening and significant=20 heavy rainfall and flash flood event remains high beginning late=20 tonight through Saturday night across portions of the Ohio and=20 Tennessee Valleys. While there is some subtle variability in the=20 placement of the heaviest QPF (northwest to southeast), some=20 clustering of the guidance happened this cycle for a swath of 3-6"=20 from western TN through central Kentucky with a signal for isolated amounts up to 8". The environment will be quite unusual for mid-February. The combination of MUCAPE of 500-1000 j/kg and PWATs reaching around 1.5 inches has only rarely been observed in KY/TN at this time of year, and would be supportive of 1-2 inch per hour rain rates in the most organized and intense convection. A powerful southwesterly LLJ over 60 knots, oriented at an acute angle to the developing warm front, will favor backbuilding into the region of stronger instability. And the overall mean flow should favor some periods of training convective clusters or bands near the warm front and surface low track. All of these ingredients are fairly classic for impactful flash flooding cases, and significant impacts are anticipated in this one as well. Given all of this, a High Risk was introduced for portions of NW TN through central KY, where life-threatening and significant flooding is anticipated. Elsewhere, not many changes were made to the Moderate/Slight Risk areas, with some pulling back out of eastern KY and the central Appalachians where the trends for less QPF continues somewhat. However, don't want to downplay that area given its sensitivity and antecedent conditions as well. Lamers/Taylor Day 3 Valid 12Z Sun Feb 16 2025 - 12Z Mon Feb 17 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF THE MID-ATLANTIC... ....Mid-Atlantic... A Marginal Risk was maintained across portions of the Mid-Atlantic region back toward the central Appalachians on Sunday, primarily due to the potential for briefly heavy rain rates with convection along an advancing cold front, and fairly low flash flood guidance values. The speed of the cold front should reduce the duration of any heavy rain, and thus any flash flood threat should remain rather isolated, however some portions of the area, particularly southwest Virginia is very saturated due to recent heavy precipitation events. Lamers/Taylor Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_AuwdfSERg7gKIuhHy1JuGaEERYpniMOZiGSbcBoAWO6= AVzG41vYQ_3BfeKzC_qaCPHn0jcwpe9Jt5dCGPLfQRBK6j8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_AuwdfSERg7gKIuhHy1JuGaEERYpniMOZiGSbcBoAWO6= AVzG41vYQ_3BfeKzC_qaCPHn0jcwpe9Jt5dCGPLfyCUIlBw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_AuwdfSERg7gKIuhHy1JuGaEERYpniMOZiGSbcBoAWO6= AVzG41vYQ_3BfeKzC_qaCPHn0jcwpe9Jt5dCGPLfrrgvLeY$=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) .