FOUS30 KWBC 090818 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 418 AM EDT Tue Jun 9 2026 Day 1 Valid 12Z 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... 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... 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