Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 21 2025 00:58:41 FOUS30 KWBC 210058 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 858 PM EDT Sun Jul 20 2025 Day 1 Valid 01Z Mon Jul 21 2025 - 12Z Mon Jul 21 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHEAST MISSOURI, CENTRAL ILLINOIS AND SOUTHWEST INDIANA... ....MS Valley into the OH Valley... The inherited Moderate risk was expanded and now includes portions of northeast MO into central IL and southwest IN. Some training=20 west to east convection is ongoing across portions of central IL=20 and adjacent areas of IN as of 01z. As we head into the overnight=20 hours convection should expand as low level moisture=20 transport/convergence increases across the region. The=20 thermodynamic environment is impressive...with MLCAPE around 3000=20 J/KG and PWs between 2" and 2.4". These ingredients will support=20 very heavy rainfall rates, with 2-3" per hour rainfall likely in=20 spots. This will be enough to result in scattered to numerous=20 instances of flash flooding as we head into the overnight hours.=20 Locally significant impacts are possible...especially if any more=20 sensitive urban or low lying areas are impacted by these intense=20 rainfall rates. There remains some uncertainty on how exactly convection will=20 evolve tonight and where any more robust training axis will set=20 up. The expansion of the MDT risk accounts for this lingering=20 uncertainty and a modest southward trend seen in some of the newer high res guidance. There is still enough run to run volatility in=20 the HRRR to keep confidence on the exact details lower...however as mentioned above, the ingredients are there for excessive rainfall=20 and potentially significant impacts. Do expect an axis of training convection to expand into the overnight hours somewhere within or=20 very close to the MDT risk area. Some flash flood impacts are also=20 likely downstream of the MDT risk across the OH valley into WV=20 through the overnight hours. ....Northern Plains...=20 Areas of stronger convection will likely move out of the High=20 Plains and into more of ND, SD and northern NE into the overnight=20 hours. Most of these cells should have enough forward movement to=20 limit the flash flood risk. Those cells that do slow and briefly=20 train should be small enough in scale that flash flooding coverage=20 into the overnight hours should stay localized. ....NM/CO... Isolated flash flooding is possible this evening from northeast NM into eastern CO where increasing coverage of slow moving cells=20 will bring areas of locally heavy rainfall. Chenard Day 2 Valid 12Z Mon Jul 21 2025 - 12Z Tue Jul 22 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF KENTUCKY, TENNESSEE, SOUTHWEST WEST VIRGINIA, & WESTERNMOST VIRGINIA... 2030Z Excessive Rainfall Discussion Update... Introduced a targeted Marginal risk area in/near the Washington Cascades over concerns of fairly modest rainfall over burn scars and regions of steep terrain from slow-moving late day storms. The numerical guidance does generate some instability to support rainfall rates that are problematic in hydrologically sensitive area. Some minor expansion was made to the Marginal risk boundary in the Southeast US and over the Ohio Valley area. Bann 0830Z Excessive Rainfall Discussion... In and near KY & TN... An axis of moisture and instability pivots between a convective frontal wave offshore the Southeast and a strengthening warm advection pattern across the Plains. Declining low-level inflow is noted with time, but the GFS forecasts enough effective bulk shear for some level of convective organization during the period of daytime heating, which doesn't drop off significantly until around sunset. Consideration the degree of saturation area soils have now and the expectation for further saturation on Sunday and Sunday night, adding a Slight Risk area here makes sense. Hourly amounts to 3" with local totals to 5" are possible where cells train or merge which would be most problematic in urban areas and over saturated soils. This appears more likely within the defined Slight Risk than the surrounding Marginal Risk area. There was some consideration for a Slight Risk for coastal sections of NC, but with coastal marsh in some of those areas, decided against it. Plains/Southern Rockies... Surface boundaries/low pressure areas/upper level disturbances are on this move this period, which along with warming temperatures at 700 hPa/increased mid- level capping across portions of the Central Plains and IA should limit QPF and flash flood potential elsewhere. Hourly amounts up to 2" and local totals to 4" are considered possible in this region. At the moment, it appears any flash flooding would be on an isolated to widely scattered basis. In the Southwest and Southern Rockies, burn scars and dry washes/arroyos would be most at risk. Anywhere within these regions, urban areas would be of most concern. Roth Day 3 Valid 12Z Tue Jul 22 2025 - 12Z Wed Jul 23 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF MINNESOTA, NORTHERN WISCONSIN, & NORTHWESTERN MICHIGAN... 2030Z Excessive Rainfall Discussion... Primary focus for excessive rainfall remains in the Upper Midwest/Western Great Lakes where increasing low level moisture transport interacts with sfc low pressure and mid-level height falls coming out of the Dakotas. The potentially convective low over the Southeast also remains a possible focus for locally heavy to excessive rainfall. The numerical guidance continued to show run to run consistency in the big picture but had less agreement on the finer details. Either way...changes to the Excessive Rainfall Outlook were minor. Bann 0830Z Excessive Rainfall Discussion... In and near the Western Great Lakes... A strengthening low-level jet out of the southwest is expected downwind of an amplified Western trough and under the base of a cold low moving across central Canada. Precipitable water values rise to 2"+ and a broad reservoir of CAPE up to 5000 J/kg builds near southeast SD due to significant warming at 700 hPa/a strengthening mid-level capping inversion across portions of the Plains to the east of the Western trough. Effective bulk shear should be more than sufficient for organized thunderstorms, including mesocyclone formation. Weekly rainfall anomalies show that portions of the Arrowhead Peninsula and Upper Peninsula of MI have had 300%+ of their average rainfall, leading to some degree of saturation. Hourly rain amounts to 2.5" with local amounts to 5" could lead to flash flooding, with urban areas most prone to issues. The Slight Risk was shifted somewhat north of continuity per the latest guidance. Southeast... A potentially convective low retrogrades through portions of northern FL this period. Precipitable water values rise to 2-2.25". CAPE should rise to 3000 J/kg due to either daytime heating where present or due to onshore flow from the warm western Atlantic, Gulf, and FL Straits. There does appear to be enough effective bulk shear present for at least some loose convective organization. Hourly amounts to 3" and local totals to 6" are possible here. Considered a Slight Risk as some portions of northern FL saw above average precipitation with the previous retrograding convective low on July 16-17, but the heavy rain signal at the moment shows minimal overlap with the the previous convective low's rainfall footprint. Southern Rockies... Enough moisture and instability is expected to hourly amounts up to 2" and local totals to 4", with a distinct diurnal cycle expected. At the moment, it appears any flash flooding would be on an isolated to widely scattered basis. Burn scars and dry washes/arroyos, and urban areas would be most at risk. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!81yRo_IduKT8zMXM7YZ7nNDzIXWvMobA6A9-jkKvVxxq= juO0A5UddNjIOjb8ifcl30Z3ky8yDkU-v3qJFaTAuNWUETc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!81yRo_IduKT8zMXM7YZ7nNDzIXWvMobA6A9-jkKvVxxq= juO0A5UddNjIOjb8ifcl30Z3ky8yDkU-v3qJFaTAy0WrgJ8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!81yRo_IduKT8zMXM7YZ7nNDzIXWvMobA6A9-jkKvVxxq= juO0A5UddNjIOjb8ifcl30Z3ky8yDkU-v3qJFaTAcePCl2M$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .