Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Dec 05 2022 00:54:32 FOUS30 KWBC 050054 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 752 PM EST Sun Dec 04 2022 Day 1 Valid 01Z Mon Dec 05 2022 - 12Z Mon Dec 05 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill Day 2 Valid 12Z Mon Dec 05 2022 - 12Z Tue Dec 06 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR FAR SOUTHERN TENNESSEE, NORTHERN ALABAMA, NORTHEAST MISSISSIPPI, AND NORTHERN GEORGIA... High pressure over the East Coast will work in tandem with low pressure over the Southern Plains to generate a southwesterly 850mb moisture moisture fetch out of the western Gulf of Mexico beneath an expansive 120 kt southwesterly jet over much of the country. Meanwhile, there is also a lingering 850mb moisture feed emanating out of the tropical East Pacific set to be oriented at the Mid-South on Monday. By 18Z Monday and lasting through Monday night, NAEFS shows an expansive swath of PWs from Texas to the TN Valley that ranges generally between 90-97.5 climatological percentiles and PW values >1.5" in the Lower Mississippi River Valley. In addition, IVT values of 500-750 kg/m/s are oriented across North Texas and through the Mid-South, which are also in the 90-97.5 climatological percentile range. While there is no shortage of anomalous atmospheric moisture and moisture transport, the key in generating excessive rainfall rates is squarely on instability. Most operational guidance focuses the highest values of MUCAPE closer to western Tennessee and northern Mississippi Monday night with values ranging as high as 500-1,000 J/kg. Farther east, instability is tougher to come by, but PWs and upslope flow into the higher terrain of northern Alabama, northern Georgia, and eastern Tennessee allow for additional precipitation rate enhancement. Soils are generally closer to normal when it comes to soil saturation, despite the swath of 300-400% of normal rainfall across northern Alabama. There is still an impressive swath of anomalous moisture available, and the westerly 850-300mb mean flow is likely to run quasi-parallel to the warm front lifting north through the Mid-South Monday evening. This could support training segments of heavy showers and/or thunderstorms if sufficient instability is available. Have opted to maintain the current Slight and Marginal Risks over the Mid-South, making subtle adjustments based on latest QPF forecasts. Mullinax Day 3 Valid 12Z Tue Dec 06 2022 - 12Z Wed Dec 07 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE TENNESSEE VALLEY... The upper trough along the West Coast begins to move into the Southwest while the strong ridging aloft over the Gulf of Mexico helps create a broad SW flow regime stretching from the tropical East Pacific to the Great Lakes. The same combination of 850mb moisture from the East Pacific and Gulf of Mexico will continue to be the source for ongoing periods of rain from the Southern Plains to the Northeast. The area most at risk for excessive rainfall remains the Tennessee Valley, where the warm sector will provide some instability (roughly 500-750 J/kg of MUCAPE) and PWs are above the 90th climatological percentile according to NAEFS. Soil moisture will also be on the increase following a day of moderate-to-heavy rainfall throughout the Tennessee Valley on Monday, making soils more sensitive to another day of potentially heavy rainfall rates. The main change to today's update is to adjust the Marginal slightly farther north into southern Kentucky were latest QPF trends have favored a modest bump inf rainfall totals. Otherwise, given the lingering uncertainty on available instability and the axis of where the heaviest rainfall totals occur, chose to hold off on any Slight Risk upgrade this forecast cycle. Farther north, rainfall totals did come up from the overnight shift in parts of the Northeast. The same conveyor belt of moisture responsible for the heavy rainfall in the Tennessee Valley is also expected to reach the Northeast, where the NAEFS also depicts PWs that are >90th climatological percentile. That said, there is even less instability available there and should keep a cap on excessive rainfall rates. Will continue to watch for any potential hints of better instability values in future forecast cycles, but for now, continued to leave out any threat areas fro Excessive Rainfall in the Northeast. Mullinax Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6IyNcBi9nc4Zk_sKHnkCmwzgGtF5nRnjpaRUQqs5wE8d= Q2twLxbUwWo7DOY5qBcet_2p0tN1iaQ5j9HAyoht_S0E2dI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6IyNcBi9nc4Zk_sKHnkCmwzgGtF5nRnjpaRUQqs5wE8d= Q2twLxbUwWo7DOY5qBcet_2p0tN1iaQ5j9HAyohtnzD6x0M$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6IyNcBi9nc4Zk_sKHnkCmwzgGtF5nRnjpaRUQqs5wE8d= Q2twLxbUwWo7DOY5qBcet_2p0tN1iaQ5j9HAyoht34dPw6k$=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) .