Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Nov 10 2023 20:21:56 FOUS30 KWBC 102021 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 321 PM EST Fri Nov 10 2023 Day 1 Valid 16Z Fri Nov 10 2023 - 12Z Sat Nov 11 2023 ....THERE IS A MARGINAL RISK OF FLOODING ALONG THE CENTRAL AND LOWER TEXAS COAST... 16Z Update... The previous discussion summarizes today's Marginal Risk threat well along the central and lower Texas coast. While instability is hard to come by, PWs according to NAEFS are impressive for early-mid November. The 12Z soundings out of BRO and CRP measured 2.11" and 2.00" PWs respectively, but there was a reduction in instability over CRP compared to BRO. PWs will reach as high as the 99.5th climatological percentile over the Lower Rio Grande Valley and as far north as Corpus Christi at 18Z today. As the cold front moves south, instability will gradually decrease over the Lower Rio Grande Valley. In addition, the 12Z RAP showed warm cloud layers along the lower Texas coast that were approaching 14,000' in depth and low-mid layer RH values >95% later this afternoon. These parameters support efficient warm rainfall processes, but the lack of instability combined with higher FFGs from drier than normal conditions over the past month will limit the flash flood potential. Flooding in pour drainage areas cannot be fully ruled out, particularly in more urbanized communities. Mullinax ---Previous Discussion--- Front pushing south across the region this morning is expected to stall near the coast today. Warm, moist southwest flow aloft will support PWs at or above 2 inches along the coast. This moisture along with large-scale ascent afforded in part by right-entrance region upper jet forcing will help generate widespread precipitation across the region. While instability will be limited, a saturated air column may support efficient rates. A Marginal Risk was introduced highlighting the area where the HREF is showing high neighborhood probabilities for additional amounts of 3 inches or more. This includes portions of the Texas coast that received locally heavy amounts yesterday and where 3-hr FFG values have dropped below 0.25 inch in some locations. Pereira Day 2 Valid 12Z Sat Nov 11 2023 - 12Z Sun Nov 12 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Mullinax Day 3 Valid 12Z Sun Nov 12 2023 - 12Z Mon Nov 13 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTH TEXAS... A potent 250-500mb upper trough over Baja California will track across northern Mexico on Sunday. It will induce vertical ascent atop the atmosphere thanks to healthy positive vorticity advection (PVA) and South Texas' placement beneath the right-entrance region of a 250mb jet streak Sunday night. Meanwhile, two sources of rich tropical Pacific moisture will be directed into South Texas. The first source region is based out of the East Pacific as 700mb moisture flux is channeled northward towards the Rio Grande Valley. The second source of moisture arrives Sunday night as easterly flow strengthens within the 850-700mb layer and an IVT of 400-500 kg/m/s is directed at the Lower Texas Coast. The result is a highly anomalous moisture regime for mid-November. NAEFS between 00-12Z Monday show PWs that are >2" along the Lower Texas Coast, which is above the 99.5th climatological percentile. PWs are not quite as high farther west towards Laredo and south of San Antonio, but PWs could still top 1.8" which is above the 97.5th climatological percentile. While there is ample synoptic scale lift present and no shortage of moisture, there remains a lack of instability. This should help to suppress torrential rainfall rates of 2-3"/hr for example, but area averaged model soundings still depict warm cloud layers could be as deep as 14,000ft AGL and low-mid level RH values >95% Sunday night. These parameters would yield efficient rainfall rates that could cause localized ponding in poor drainage areas and more urbanized settings. The region also does not feature quite as dry of soils thanks to recent heavy rainfall the past couple days. The latest NBM sported 40-50% probabilities for >3" of rainfall from Laredo on east to the central Texas Coast, and the bulk of this rainfall occurring between 00-12Z Monday. Given these factors, a Marginal Risk was introduced for South Texas. Mullinax Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_QKEJbeZhRawcJTy49c-8BDE0rOp8wYBOWn8xpKW3fiL= SrBMSnTiKkvOSbEVasLIxaqCYJM5FX2LynNAlyGy76Qmt6Y$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_QKEJbeZhRawcJTy49c-8BDE0rOp8wYBOWn8xpKW3fiL= SrBMSnTiKkvOSbEVasLIxaqCYJM5FX2LynNAlyGy2uw-Gp0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_QKEJbeZhRawcJTy49c-8BDE0rOp8wYBOWn8xpKW3fiL= SrBMSnTiKkvOSbEVasLIxaqCYJM5FX2LynNAlyGyOkTtfo8$=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) .