Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Nov 24 2022 08:19:46 FOUS30 KWBC 240819 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 319 AM EST Thu Nov 24 2022 Day 1 Valid 12Z Thu Nov 24 2022 - 12Z Fri Nov 25 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN TEXAS INTO THE LOWER MISSISSIPPI VALLEY... A multi-day heavy rainfall event is expected to develop over the next 48 hours across portions of Texas and the Lower Mississippi Valley. Aloft, an active subtropical jet will remain positioned across eastern Texas to the Lower MS Valley, positioning the coastal regions in the favorable right entrance region of the 120-130 kt jet today. Meanwhile, southeasterly to southerly flow on the backside of the eastern U.S. high will allow anomalously high moisture to be lifted into the region as a warm front slowly moves northward. PWs between 1.7-1.9" with some isolated signal for 2"+ values will be near 3 standard deviations above normal for this time of year while upwards of 1500 J/kg of MUCAPE is likely along the coast and areas immediately inland (though will likely drop off quickly further north, limiting the intensity of the heavy rainfall). Convection is expected to develop later this morning or early afternoon across portions of the mid/upper Texas coast and track northeast/easterly across southern Louisiana into southern Mississippi later this evening and tonight. Some of this convection will have the potential to train and repeat over the same areas with the mean flow ending up near parallel to the expected storm motions. The environmental ingredients (sustained lift, anomalous moisture, and instability) supports intense rain rates approaching 2"/hr at times with an isolated signal for 2-3" hourly totals based on the 00Z HREF probabilities. An axis of 3-5" is likely across the mid/upper TX coast through southern LA and southern MS with some potential for isolated 5-6"+ totals where repeating rounds occur. This could lead to isolated to scattered instances of flash flooding today, particularly highly urbanized corridors and other sensitive locations. Further north across northeast Texas, moderate to locally heavy rainfall will likely repeat over the same area through early afternoon with some potential for hourly totals greater than 1" at times and totals of 2-3".=20 Taylor Day 2 Valid 12Z Fri Nov 25 2022 - 12Z Sat Nov 26 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF CENTRAL TEXAS TO TEXAS GULF COAST... An anomalously deep closed low will approach and stall over Texas during the day 2 period which will be the driving factor for the second round of heavy rainfall potential in the region. East of the closed low, a broad area of forcing for ascent is expected across Texas in the highly divergent upper flow pattern. In the low levels, very moist flow aided by 20-40 kts at 850 mb will bring a renewed surge of moisture into Texas with the latest guidance showing precipitable water values exceeding 1.5" with some values near 2" likely along the immediate coast overlapping with an axis of higher instability. The near stationary closed low during the period will allow a slow moving axis of convection to set up from portions of central Texas toward the mid/upper Texas coast with the increasingly likely scenario that some areas could see a prolonged period of training heavy convection along the coast especially Friday afternoon through early Saturday morning. Model guidance however continues to struggle with the timing and speed of this system, with this forecast cycle seeing another significant slow down and shift south/southwest in the axis of heaviest precipitation. As such, it's a lower confidence set up which is typical with closed upper lows. However, the ingredients and conceptual model suggests a signal for heavy rainfall but exact location and details precluded anything higher than a Slight Risk at this time. It's possible a higher risk category may needed in future updates if the overlap of heaviest QPF between what materializes today and what is expected during day 2 is greater or if confidence in setup/location increases. The most concerning location right now looks to be along the mid/upper Texas coast where an additional 2-4"+ could fall during the day 2 period resulting in 48-hr (12Z Thursday-12Z Saturday) totals of 4-5" with localized 6-8"+ totals. Taylor Day 3 Valid 12Z Sat Nov 26 2022 - 12Z Sun Nov 27 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER MISSISSIPPI RIVER VALLEY... The closed upper low over Texas finally begins to kick out to the northeast during the day 3 period, aided by the approach of another shortwave trough quickly progressing through the western U.S. and reaching the Plains by the end of the period. As the compact upper low lifts northeast, its associated area of low pressure is forecast to track from eastern Texas to the lower Great Lakes. Ahead of that, an axis of higher moisture is likely with upwards of 1.5" PWs forecast. The combination of the strongly divergent upper flow resulting in a broad area of forcing for ascent and the anomalously high moisture (PWs near 2 sigma above normal) will help bring locally heavy rainfall to portions of eastern Texas to the lower and mid Mississippi Valley. A broad area of 1" to locally 2" of rainfall will be possible which may lead to very localized flash flood concerns, though the intensity of the rainfall is likely to be limited somewhat by the lack of deep instability and the increasingly fast speed as the storm system becomes more progressive. Nonetheless, some isolated instances of flash flooding will be possible for the more susceptible or vulnerable locations within the Marginal Risk area. Taylor Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_0n-jHBDtRHi46Vwukvfdg5XiDmQIv2UHC4B-BvQAjwe= yLgD8nqS2IHQ4JVpOcl4b3nVTritEYK2UVZmQLRqihhEg3E$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_0n-jHBDtRHi46Vwukvfdg5XiDmQIv2UHC4B-BvQAjwe= yLgD8nqS2IHQ4JVpOcl4b3nVTritEYK2UVZmQLRqUeRl4W0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_0n-jHBDtRHi46Vwukvfdg5XiDmQIv2UHC4B-BvQAjwe= yLgD8nqS2IHQ4JVpOcl4b3nVTritEYK2UVZmQLRq5emJ43o$=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) .