Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Oct 08 2023 08:21:30 FOUS30 KWBC 080821 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 420 AM EDT Sun Oct 08 2023 Day 1 Valid 12Z Sun Oct 08 2023 - 12Z Mon Oct 09 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE ATLANTIC COAST OF SOUTHEAST FLORIDA AND PORTIONS OF CENTRAL NEW YORK EAST OF LAKE ONTARIO... ....Central New York... No significant changes were made to the Marginal Risk areas in NY and FL. In NY, in collaboration with BUF/Buffalo, NY forecast office, the Marginal was left in place east of Lake Ontario. As the extratropical remnants of Philippe track northwestward into Quebec, it will draw cold air with 850 temps to -3C over the Great Lakes. The Lake Ontario water temperature is 68F, or 20C. This 23C temperature difference will result in extreme instability developing as the cold air moves over the warm waters of the lake. Lake enhancement has already started across Oswego County, and will intensify today as the low center approaching the Maine coastline tracks into central and western Quebec. The band will gradually drift northward today from Oswego and Lewis counties up to Jefferson county tonight. The extreme instability will allow the lake enhancement to grow convectively, resulting in localized heavy rain, which as is the nature of lake-effect may repeat over the same areas. For the Tug Hill Plateau region, upslope enhancement may locally further increase rainfall rates. Except in a small swath of Lewis and Oneida counties, soils in this area are still drier than normal despite recent rainfall. Thus, at first the ongoing rainfall will be beneficial, but in those areas where the heaviest rainfall lingers longest, isolated flash flooding is possible. ....Southeast Florida... A front currently nearly stalled out over central FL will act as a conveyor belt for deep Gulf moisture to ride northeastward along and south of the frontal interface today. Low level easterly flow will create an area of frictional convergence along the coast in the Miami-Ft. Lauderdale area. CAMs guidance shows that there's potential for strong thunderstorms that may linger over those urban areas, resulting in multiple inches of rain in a short period over a flood-sensitive area, though they have backed off on the potential in the latest runs. The Marginal Risk area remains unchanged with this update, and is low-confidence. Wegman Day 2 Valid 12Z Mon Oct 09 2023 - 12Z Tue Oct 10 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 Valid 12Z Tue Oct 10 2023 - 12Z Wed Oct 11 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE LOWER TEXAS GULF COAST... A surge of moisture associated with Potential Tropical Cyclone 16-E in the eastern Pacific will track northward across Mexico into the western Gulf, and into the Texas Gulf Coast by Tuesday night. Meanwhile a strong and nearly stationary upper level jet will be centered over the Tennessee Valley, which will put south Texas in the favorable right entrance region. Thus, rain along the TX Gulf Coast may begin in Deep South Texas as early as Monday night/very early Tuesday morning, and will gradually intensify as it lifts north closer to the favorable jet dynamics through the day Tuesday. Finally, by Tuesday night, the aforementioned remnants of PTC 16E will reach the northwestern Gulf/Texas Gulf Coast. This influx of moisture will greatly enhance rainfall rates as PWATs skyrocket to as high as 2.5 inches Tuesday night. There remains significant uncertainty as to the track of the low, and how far west the associated heavy rainfall can move inland from the Gulf Coast. Since confidence has increased markedly as to the rainfall threat along the immediate Gulf Coast, a Slight Risk area representing a double upgrade was introduced for that area in coordination with CRP/Corpus Christi, TX forecast office. The surrounding Marginal represents the considerable uncertainty as to how far north and west the heavier rains will get, and is likely to change with future forecast updates. Soil moisture across Deep South Texas is above normal due to recent rainfall, so the addition of 3 to 5 inches of rain with higher local totals is likely to result in widely scattered instances of flash flooding, especially along the Gulf Coast and any urbanized areas, such as Corpus Christi and Brownsville. This increased the confidence enough to warrant the Slight Risk upgrade for this area. There is good agreement that this should be a one-day event for the Texas Gulf Coast, as the greatest moisture associated with the low quickly shifts east into the eastern Gulf on Day 4/Wednesday. That said, the moisture associated with the other eastern Pacific tropical cyclone, T.S. Lidia will be following on the heels of PTC 16E, so that will need to be monitored for the Wednesday/Wednesday night time frame. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!91MvHxmM5ZfUy3KE7zffP9yvsBmOJ7QJzgnLZVdhdthb= ndzOf7GcM4Yda3Y7Nm9igsSFuKFGdHspBFRyvqy3Yu4VaFo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!91MvHxmM5ZfUy3KE7zffP9yvsBmOJ7QJzgnLZVdhdthb= ndzOf7GcM4Yda3Y7Nm9igsSFuKFGdHspBFRyvqy32uxXEz0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!91MvHxmM5ZfUy3KE7zffP9yvsBmOJ7QJzgnLZVdhdthb= ndzOf7GcM4Yda3Y7Nm9igsSFuKFGdHspBFRyvqy3pkyKju0$=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) .