Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jun 10 2025 08:22:33 FOUS30 KWBC 100821 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 421 AM EDT Tue Jun 10 2025 Day 1 Valid 12Z Tue Jun 10 2025 - 12Z Wed Jun 11 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF TEXAS... Multiple rounds of showers and thunderstorms will impact portions of southern and western Texas today into tonight. The first round ongoing now in west Texas may persist in a weakened and likely non-impactful form (from a flooding perspective, at least) past 12Z this morning across central Texas. Generally the only expected impact from these storms will be a priming (or continued saturation) of the soils.=20 New storms may begin to develop as early as midday across the Trans-Pecos and Edwards Plateau regions of west Texas. They'll develop in large part due to an influx of deep Gulf moisture into southwest Texas, with PWATs up to 1.5 inches, or about 2 sigma above normal for that area of west Texas. This amount of atmospheric moisture along with maximum solar heating for this time of year will allow instability to become extreme in some areas, likely exceeding 4,000 J/kg. Thus, in addition to any severe threat, the storms will be more than capable of producing very heavy rain, with rates of 3+ inches per hour with the strongest=20 storms. The storms will likely congeal in the Edwards Plateau region late in the afternoon, generally following the Rio Grande south and east. With atmospheric moisture only increasing as the storms move towards the Gulf, they will remain prolific rainmakers well into the overnight hours. Soils across the Edwards Plateau and south-central Texas are very dry, with most of the recent heavy rainfall occurring well north of this area. While this will work to inhibit riverine flooding, the soils should initially be quite hydrophobic because they've been so dry, increasing the flash flooding threat. Thus, a higher end Slight is in effect for the area from San Antonio west to the Rio Grande. Elsewhere, a stalled out front just inland from the Gulf Coast in the Southeast may act as a catalyst for additional convection from Houston east to the Carolinas. Despite the presence of the front, there will be little to organize the storms, which will still have plentiful tropical moisture to work with, so the Marginal Risk was maintained. Further north, drier air should preclude any flooding along the Delmarva, while the forcing remains west of Maine...so those areas were removed from the Marginal with this update. Wegman Day 2 Valid 12Z Wed Jun 11 2025 - 12Z Thu Jun 12 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF TEXAS AND SOUTHERN OKLAHOMA... A strong low-level jet will continue to advect abundant Gulf moisture northward across the southern Plains on Wednesday. This moisture will run into the dryline across west Texas, which in turn will result in renewed rounds of convection forming along the dryline, or remnant cold pool boundaries from prior convection. The new storms will drop their own cold pools, likely causing additional convection. Since moisture replenishment will be constant, the storms should have no trouble maintaining themselves as they move across Texas. Expect at least some morning convection to be ongoing at the start of the period from the overnight storms in Day 1. However, as on previous days, the lion's share of the heavy rainfall across Texas will result from afternoon convection congealing into one or more MCSs during the overnight period when the LLJ ramps up.=20 The primary source of uncertainty, as is very common with convection, is where the convection forms. Depending on the guidance, that could be anywhere across the eastern half of Texas. While the consensus is along the I-35 corridor from south of San Antonio to the Oklahoma state line, the variance longitudinally is from the Permian Basin to the Louisiana state line. This uncertainty with both where the convection will form and how organized it will be largely precluded any potential Moderate Risk upgrades, although several urban areas including the Metroplex,=20 Waco, Austin, and San Antonio may all have a higher flash flooding=20 threat. Further, the signal for heavy rain has decreased somewhat, which also reduced any confidence in any upgrades at this time. Elsewhere across the Southeast, the abundance of atmospheric moisture all along the Gulf Coast should support almost any=20 convection having at least some potential to cause isolated flash=20 flooding. Given that and somewhat higher rainfall amounts forecast, the Marginal Risk was expanded greatly to include the rest of the=20 Gulf Coast and up the Atlantic coast to North Carolina with this=20 update. Tidal flooding with the full Strawberry Moon may compound=20 any flooding from rainfall at the shore. The Marginal Risks in the upper Midwest and across much of Montana were largely unchanged with this update. The LLJ, or an extension thereof will provide moisture for storms to draw from in both these areas, as upper level shortwave disturbances provide the forcing for those storms to form and loosely organize. Drier soils in these areas should preclude all but an isolated flash flooding threat. Other than the extension of the Marginal Risk in the Southeast, changes elsewhere were minor, with a southward nudge to the Slight in Texas. Wegman Day 3 Valid 12Z Thu Jun 12 2025 - 12Z Fri Jun 13 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS AS WELL AS FOR SOUTHERN MINNESOTA... ....Southern Plains... A rinse and repeat pattern across Texas will continue on Thursday as plentiful Gulf moisture from an increasingly strong LLJ continues to advect northward across the southern Plains. It appears that the storms will shift slightly further east as compared to Wednesday, but the I-35 corridor from San Antonio through the Metroplex to Oklahoma City appears to still be in the bullseye for the most rainfall, especially in Texas. While a higher-end Slight remains in effect across this area, should current rainfall amounts hold, then a Moderate Risk may eventually be needed as the effects from multiple consecutive days featuring storms dropping heavy rain lower the thresholds needed for additional flash flooding to develop. Once again the guidance is all over the place, which is fairly normal for a Day 3 forecast for convection in the summer. Thus, for now, will hold off on any upgrades. What can be said is by this point, a more well defined corridor of heavier rain appears likely to have developed, generally tied to a dry line that inches eastward with each passing day.=20 ....Southern Minnesota... Forecast rainfall amounts have increased significantly across southern Minnesota as the guidance suggests a mesolow forms across Nebraska/South Dakota/Iowa and slowly drifts east, latching on to the northern extent of the plume of Gulf moisture gradually expanding across much of the Southeast by Thursday. This low will provide the forcing, with plentiful moisture and a decent frontal boundary to its north all acting to support training and backbuilding thunderstorms across southern Minnesota, including the Twin Cities. With some potential for overlap on the southern side of the storms with rainfall from the Day 2/Wednesday period, and the rapid increase in forecast rainfall, a Slight Risk upgrade was introduced with this update. Storms are likely to develop further west back across the Dakotas and eastern Montana, but the greatest forcing and thus, highest risk of flash flooding will be into Minnesota. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7CEBJAsByiNZz1ikzJgZ_VWf1lLgvIL3aepA1dYTE1Y8= OR9Sk1u3LurdjiQGZwXoDLEcMED1pzAPHUX2EkRPcM9dhak$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7CEBJAsByiNZz1ikzJgZ_VWf1lLgvIL3aepA1dYTE1Y8= OR9Sk1u3LurdjiQGZwXoDLEcMED1pzAPHUX2EkRP4Uo8ETY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7CEBJAsByiNZz1ikzJgZ_VWf1lLgvIL3aepA1dYTE1Y8= OR9Sk1u3LurdjiQGZwXoDLEcMED1pzAPHUX2EkRPjWD7ox8$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .