Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jun 11 2025 00:19:00 FOUS30 KWBC 110018 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 818 PM EDT Tue Jun 10 2025 Day 1 Valid 01Z Wed Jun 11 2025 - 12Z Wed Jun 11 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF TEXAS... ....01Z Update... Pared a bit of the Marginal Risk area, including portions of the=20 Gulf Coast region from the Upper TX Coast through central LA, based on the latest observational trends (mosaic radar/satellite/mesoanalysis) and current HRRR/HREF output. Given the sub-7.0 C/KM mid level lapse rates along with 0-6km bulk shear values of 25kts or less, predominately pulse-variety convection=20 will wane significantly in intensity and areal-extent after sunset per the negative dCAPE/dt trends from the latest SPC mesoanalysis. Slight Risk area area across TX still looks good, though per the latest observational and guidance trends, did include a little=20 more of South TX along the Rio Grande.=20 Hurley Previous discussion... ....Texas... Another round of showers and thunderstorms will impact portions of southern and western Texas this afternoon into tonight. Ongoing=20 convection over northeastern Texas is slowly weakening though new=20 activity is developing downstream over LA along an elevated=20 boundary. New storms should develop this afternoon across the Trans-Pecos and Edwards Plateau regions of west Texas. Deep Gulf moisture (PW values > 1.5" or +2 sigma) combined with maximum solar heating 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 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. 12Z HREF probs still show 3"/hr probs >30% in some areas. 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. 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... ....Texas into the Southeast... 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 which have acted to increase soil moisture (and lower FFG values). 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. 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 and has not yet converged even with another cycle of guidance. 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, Waco, Austin, and San Antonio may all have a higher flash flooding threat. Further, their remains a separation (north-south) between the HREF guidance and RRFS ensemble guidance, which also reduced any confidence in any upgrades at this time. However, the rather high 10th percentile amounts nearing 0.75-1.00" around and just south of the Metroplex does decrease the potential for just Marginal impacts. 90th percentile QPF was well above 4-6" with some more aggressive CAMs showing closer to 10" over the 24-hr period. Both the GEFS M-Climate QPF (near max values) and ECMWF EFI/SoT (0.7-0.8/near 1) suggest that potential is real. Elsewhere across the Southeast, the abundance of atmospheric moisture all along the Gulf Coast should support almost any convection having at least some potential to cause isolated flash flooding. Tidal flooding with the full Strawberry Moon may compound any flooding from rainfall at the shore. Maintained the expansive Marginal Risk that also includes Florida where a modest surge in moisture may support heavier rain totals over southern/southwest portions of the state. ....Western High Plains and the Corn Belt... 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. However, more sensitive areas along the Divide/Northern Rockies would also be at risk from comparatively less QPF than farther east. Wegman/Fracasso 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... Mid-level shortwave will slowly move through the area Thursday but will favor a similar area in eastern Texas as day 2. 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 was maintained across this area, a Moderate Risk areas may be needed depending on how the rainfall footprint evolves over the next two days. The guidance is all over the place, which is fairly normal for a Day 3 forecast for convection in the summer, with hints of a north-south bifurcation in the QPF (e.g., GFS, RRFS, and ECMWF-AIFS QPF). ....Southern Minnesota... Northern extent of the plume of Gulf moisture will surge northward and intersect a mid-level shortwave and surface boundary from southern SD eastward into southern MN. This setup will support training and backbuilding thunderstorms across southern Minnesota, including the Twin Cities, on Thursday. With some potential for overlap on the southern side of the storms with rainfall from the Day 2/Wednesday period, the Slight Risk was maintained from overnight. Model QPF was quite displaced north-south across MN (e.g., NAM, GFS, and RRFS farther north) but will hedge on the southern side of the QPF spread closer to the better instability (and playing into the typical bias). 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/Fracasso Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5RC8m2kOnRfggO2jfCEdmq0NAiJOhSUQNbPoivAsu1oM= QWTAC4iPTdsvwwoRdH3t1HosCTOrsUKi_0PT_TvS1i6gnC8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5RC8m2kOnRfggO2jfCEdmq0NAiJOhSUQNbPoivAsu1oM= QWTAC4iPTdsvwwoRdH3t1HosCTOrsUKi_0PT_TvS0234Q8Y$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5RC8m2kOnRfggO2jfCEdmq0NAiJOhSUQNbPoivAsu1oM= QWTAC4iPTdsvwwoRdH3t1HosCTOrsUKi_0PT_TvSgSXOxbk$=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) .