Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Oct 09 2023 00:51:12 FOUS30 KWBC 090051 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 850 PM EDT Sun Oct 08 2023 Day 1 Valid 16Z Sun Oct 08 2023 - 12Z Mon Oct 09 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley 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/Kleebauer Day 3 Valid 12Z Tue Oct 10 2023 - 12Z Wed Oct 11 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTH TEXAS... The overall synoptic pattern remains steadfast with the latest guidance, but an uptick in the overall QPF field was the biggest change from the previous forecast cycle. The magnitude of rainfall is still within the premise of 3-5" with locally higher amounts, but the spatial coverage of the heavier QPF footprint has expanded further inland, back towards the Rio Grande. GEFS ensemble guidance has become increasingly bullish on the higher totals based off the increase in forecast ensemble precip, as well as associated probabilities for both >2" (20-30%), and >3" (10-15%) totals within the 24 hr period. When you factor in the main time frame for precipitation is back-loaded to the second half of D3, that creates a reasonable forecast for heightened flash flood concerns given the short time frame the heavy precip will fall. PWATs continue to be impressive within the means showing a 2.25-2.5" PWAT outline from KCRP to Eagle Pass and points south. This environment is of tropical origin which creates a higher potential for efficient warm processes and higher QPF probabilities. Would anticipate a further increase in the QPF footprint so long as the synoptic scale setup remains the same. Considering the shift in the heavier precip field further inland, have expanded the SLGT risk out to the RGV and will now encompass most of WFO Corpus Christi's CWA and all of WFO Brownsville's CWA. The SLGT was outlined using a blend of the NBM/GEFS/Ensemble bias-corrected QPF field with the edges defined with the 1.25" QPF contour. Kleebauer ....South Texas... 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!5mcJsTUf_8ZW6aS8kMtKF3_jziuUH48Q10DFSIfCJWVc= VX5rOcWD8TZ6xrYAUPHHAV6nlFP6I5tyQmPrvb_ZjlN6d20$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5mcJsTUf_8ZW6aS8kMtKF3_jziuUH48Q10DFSIfCJWVc= VX5rOcWD8TZ6xrYAUPHHAV6nlFP6I5tyQmPrvb_Z25o64xA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5mcJsTUf_8ZW6aS8kMtKF3_jziuUH48Q10DFSIfCJWVc= VX5rOcWD8TZ6xrYAUPHHAV6nlFP6I5tyQmPrvb_ZU0J4j_4$=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) .