FOUS30 KWBC 091540 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1140 AM EDT Tue Jun 9 2026 Day 1 Valid 16Z Tue Jun 09 2026 - 12Z Wed Jun 10 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE NORTHERN PLAINS, OHIO AND TENNESSEE VALLEYS, AND SOUTHERN APPALACHIANS... .Northern Plains... 16Z Update: The trends in guidance maintain a signal for locally heavy rainfall over portions of North Dakota into northern MN later this evening. Progressive nature of the convection may limit the expanse of significant flash flood potential, however anomalous deep moist environment coupled with the energetic nature of the disturbance and a very buoyant environment will likely enhance convective cores, providing capability for rates to exceed 2"/hr in the strongest cells. CAMs have been generous with local amounts between 3-5" in the areas hardest hit with the bullseye focused over northeastern ND, so it's very plausible to see at least a few flash flood warnings arise in this setup. The previous SLGT risk was general maintained with some trimming of the southwestern flank to account for trends in the 12z CAMs indicating a local min just to the northeast of Bismarck. Kleebauer ..Previous Discussion.. A potent upper level trough will push across the northern Rockies into the Plains today and spur cyclogenesis over the northern Plains. Low pressure will strengthen over the region with a cold front extending to the southwest and a warm front extending to the east. Southerly winds ahead of the trough will direct warm, moist, unstable air into the northern Plains, with PWAT values expected to exceed 1.5 inches and MUCAPE expected to rise above 3000 J/kg. Increasing mid/low level winds on the leading edge of the trough will create a highly sheared environment that is conducive for supercell development this afternoon. By this evening, an intensifying low level jet oriented parallel to the surface cold front will support upscale convective growth into a linear MCS. Deep convection within supercells and eventually the more organized MCS will be able to tap into the atmospheric moisture to produce very intense rainfall rates in excess of 2 inches per hour. Relatively fast storm motion will be a limiting factor to the flash flood risk, but rainfall rates will be enough to overwhelm FFGs and cause flash flooding, especially if heavy rain occurs in urban environments. A Slight Risk of excessive rainfall remains in effect for the heaviest convective activity expected over central and eastern North Dakota and northwestern Minnesota. A broader Marginal Risk area extends into the Midwest where convection may focus along a surface boundary extending from the northern Plains cyclone tonight. .Ohio and Tennessee Valleys and Southern Appalachians... 16Z Update: First of two shortwaves are currently impacting the southern Ohio Valley this morning with the most notable zone of impact focused between the Ohio River basin near and west of Louisville into west-central KY between the I-65/75 corridors. 12z HREF was very aggressive in a signature of a pronounced 1-2 punch during the period with neighborhood probabilities for >3" showing a broad axis of 80+% across much of western KY and even some moderate probs for >5" (40-60%) located near and along the I-65 corridor. Very buoyant environment will be situated over the region for the entirety of the forecast with SBCAPE indices between 2000-3000 J/kg likely to encompass the area of interest. Heavy precip chances will expand away from the above areas, as well, with the prospects for rainfall rates between 1-3"/hr expanding north and northwest across southern IN/IL, as far south as north-central TN, and as far east as southern WV as enhanced theta_E advection on the western and northern flank of the ridge over the Southeast will control the overall pattern and subsequent mean flow of any activity that materializes. The SLGT risk remains over a broad area of the southern Ohio Valley and neighboring Tennessee Valley with a high- end SLGT threshold pin-pointed across the western two-thirds of KY with emphasis on that zone between the I-65 and I-75 corridors down to the TN state line. Other area of interest in the period will lie across eastern GA up through the SC and western NC Piedmont where persistent south to southeasterly flow around the ridge will maintain a narrow tongue of elevated instability and deep moist advection that has maintained a round of heavy convection this morning. This threat will last for another 2-4 hours before dissipating, but maintained the SLGT to account for what is already occurring. Kleebauer ..Previous Discussion.. An upper level trough will lift northeast across the Midwest and Great Lakes region today accompanied by a surface low over the Great Lakes and a slow-moving warm front extending south into the Ohio and Tennessee Valleys. The air mass in place across these regions will be anomalously moist with PWAT values around 2 inches, 2-2.5 standard deviations above normal for this time of year. There will also be sufficient synoptic forcing and instability to support scattered to potentially widespread convection from the Great Lakes to the Interior Southeast. Convection will be ongoing at the start of the period and should translate east throughout the day as the system progresses. High moisture content in the atmosphere will support chances for locally heavy rainfall, and more intense rainfall may be possible over the Ohio and Tennessee Valleys where convection will be enhanced by a couple quick-moving mid-level waves rounding the top of the ridge positioned over the Gulf. The first wave will pass over the region early in the period, resulting in a burst of more intense convection this morning. The second wave will pass over this area tonight into early Wednesday morning and will have the potential for back-building storms along a surface boundary extending into the lower Ohio Valley from the northern Plains cyclone. Hi-res guidance suggests rainfall rates of 2-3 inches will be possible in stronger cells, and most hi-res CAMs are showing a swath of rainfall totals of 3-5 inches, with locally higher amounts, across portions of Kentucky and maybe southern Indiana as well. The HREF and RRFS are both showing relatively high probabilities (50-70% and 40-50% respectively) of 24 hr totals exceeding 5 inches in this area. Enhanced convection will also be possible, but to a lesser extent, under the upper waves over Tennessee and in upslope areas of the southern Appalachians. Some areas may be more susceptible to heavy rain today after recent heavy rains over the past few days. A Slight Risk of excessive rainfall covers the area of enhanced convection over the Ohio and Tennessee Valleys and southern Appalachians and a Marginal Risk area extends north through the Great Lakes. Dolan Day 2 Valid 12Z Wed Jun 10 2026 - 12Z Thu Jun 11 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR NORTHEASTERN KANSAS, SOUTHEASTERN NEBRASKA, NORTHERN MISSOURI, AND SOUTHERN IOWA... .Midwest and central Plains... On Wednesday, the northern Plains cyclone will move into south- central Canada and push a trailing cold front across the Midwest. Showers and storms will be ongoing Wednesday morning ahead of the system over northern Minnesota, then another round of convection is expected across the Midwest and central Plains Wednesday afternoon and evening ahead of and along the cold front. Deep southerly flow ahead of the system will increase PWAT values to 1.5-2 inches, with the higher values focused between northern Missouri and southern Wisconsin. Instability should increase through the afternoon as daytime heating kicks in, but the best instability (3000-4000 J/kg) looks like it will focus from eastern Kansas and southeastern Nebraska into northern Missouri and southern Iowa, where there is a Slight Risk of excessive rainfall. This area will likely experience a period of enhanced convection Wednesday night as a frontal wave develops at the intersection of the cold front and a dryline. A secondary wave of moisture and instability will surge into the central Plains as a low level jet strengthens Wednesday night, which should support efficient rainfall rates, potentially exceeding 2 inches per hour, that could lead to scattered instances of flash flooding. There is still some uncertainty regarding rainfall totals within the Slight Risk area. If the frontal wave is more progressive, the risk of flash flooding may be limited. A broader Marginal Risk area surrounds the Slight Risk and extends up through the Midwest where strong convection could result in at least isolated instances of flash flooding. .Tennessee Valley and southern Appalachians... Convection should be ongoing across portions of the Tennessee Valley and southern Appalachians at the start of the period. A quick-moving upper level wave will round the top of the ridge positioned over the Gulf and support a period of enhanced convection late Tuesday night into Wednesday morning. Anomalous moisture and sufficient instability will be in place to support efficient rainfall rates, and slow storm motions will contribute to high rainfall totals. There will also be some potential for back- building storms along a surface boundary extending from the northern Plains/southern Canada cyclone into the Tennessee Valley, mainly focusing over Kentucky. Showers and storms will also be enhanced by upslope flow along the southern Appalachians. Convection should start to weaken Wednesday morning and wane by Wednesday afternoon, but there will at least be enough rainfall over saturated soils to continue a Marginal Risk of excessive rainfall into Wednesday morning. .Interior Northeast... A Marginal Risk of excessive rainfall was introduced for portions of the Interior Northeast. An upper level trough will cross over the Great Lakes into southeastern Canada accompanied by a surface low pressure system that will bring precipitation chances to much of the Northeast. The warm sector of this system will be characterized by an anomalously moist air mass with PWAT values up to 2 inches. There should be enough moisture and synoptic forcing to support locally heavy rainfall in stronger convection near the low pressure center over southeastern Canada and the Interior Northeast. Rainfall totals and flash flood potential may also be increased by terrain and upslope flow Wednesday afternoon. Dolan Day 3 Valid 12Z Thu Jun 11 2026 - 12Z Fri Jun 12 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEASTERN MISSOURI THROUGH EASTERN IOWA AND NORTHERN ILLINOIS TO SOUTHERN WISCONSIN... The frontal wave that developed over the central Plains Wednesday night will progress northeast and intensify as a strong upper trough swings into the northern and central Plains Thursday morning. A strong low level jet will increase moisture and instability across the central Plains Wednesday night, and this air mass will expand towards the Upper Midwest as southerly winds surge ahead of the surface frontal boundary. A large swath of high PWAT values above 2 inches will stretch from the southern Plains to the Midwest, which will support a broad area of convection capable of producing locally heavy rainfall. A wave of deeper convection will accompany the strong frontal wave as it progresses, resulting in high rainfall totals over an area from northeastern Missouri through eastern Iowa, northern Illinois, and southern Wisconsin. These areas are highlighted by a Slight Risk of excessive rainfall to account for enhanced convection capable of producing scattered instances of flash flooding. A broader Marginal Risk of excessive rainfall surrounds the Slight and includes much of the Midwest and portions of the central and southern Plains. Dolan Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt $$