051 FOUS30 KWBC 110714 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 314 AM EDT Tue Aug 11 2026 Day 1 Valid 12Z Tue Aug 11 2026 - 12Z Wed Aug 12 2026 ...THERE ARE A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE OHIO VALLEY... ...Midwest/Ohio Valley/Mid-Atlantic States... The general flow pattern remains fairly static since yesterday. The equatorward edge of the Westerlies is forecast to lie from the Northern Plains into portions of the Ohio Valley and Mid- Atlantic States where there is also low- level confluence, difluent 1000-500 hPa thickness, and an instability gradient to focus organized convection. Precipitable water values are forecast to be 2"+ in spots. Hourly rain amounts to 3" and local totals to 6" remain possible given the available ingredients. Previous days' rains over these areas have saturated the soils further across portions of northern IL/northern IN/OH/WV/southwest PA. When combined with the general very flashy nature of the rivers/terrain of West Virginia, the Moderate Risk level continues to make sense. Recent guidance led to some southward shift/expansion in the Slight/Moderate Risk areas. An eastward expansion of the Slight Risk area into Richmond/ Baltimore/Washington DC was made as several members of the global guidance had a heavy rain signal over or very near the region which received heavy rainfall on Monday. ...Southern Arizona... Southeast AZ remains most at risk for more persistent heavy rainfall, so left the Slight Risk intact. Across the Great Basin, the Marginal Risk was broadened as moisture subtly increases as an upper level trough settles in to the CA Coast and ridging near the Four Corners weakens, which should lead to less mid-level capping and broader convective coverage. Roth Day 2 Valid 12Z Wed Aug 12 2026 - 12Z Thu Aug 13 2026 ...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS IN AND NEAR PORTIONS OF THE OHIO VALLEY AND SOUTHEAST ARIZONA... ...Portions of the Plains/Ohio Valley/Midwest/Corn Belt... On Wednesday, broad cyclonic flow expected to persist across the northern tier of the Lower 48 from the Northern Plains/Upper MS Valley, eastward through the Midwest/Great Lakes and into the Northeast, to the south of a closed mid-level low that has shifted into Quebec. A frontal boundary will lie along the southern periphery of this broad trough from portions of the Northern and Central Plains into portions of the Ohio Valley and Appalachians. Embedded shortwaves in this broad cyclonic flow will accentuate lift in the vicinity of this front where PW values are expected to rise to ~2" ahead of each set of shortwaves and low- level confluence is expected. The guidance continues to show a signal for heavy rainfall that at the moment is most centered over the NE Sand Hills. Due to the hydrology there, thought it prudent to maintain the inherited Marginal Risk. When looking at the ingredients, organized convection looks most likely near portions of the Ohio Valley and the Corn Belt Wednesday into Thursday morning, where the better 1000-500 hPa thickness difluence is forecast to remain. Hourly rain amounts to 3" and local totals to 6" remain possible. A high end Slight Risk lies across portions of the region due to previous days of rains further saturating soils. Spread remains in the guidance concerning QPF magnitude, so allowed to existing risk levels to ride, though there was some southward nudging to the Slight Risk positioning based on the recent guidance. ..The West/Central & Northern High Plains... A broadening upper level trough is forecast across portions of the West and Great Basin Wednesday into Thursday morning. Broad Marginal Risk areas exist near and ahead of this upper level trough for portions of the Southwest and Great Basin. Increased upper level troughing opens the door to strengthening low-level level flow and broader convective development/coverage across the West and High Plains when compared to previous days as the mid-level cap further erodes, with upslope flow developing across portions of the High Plains. Above average precipitable water values slowly shift northward through the Intermountain West. While there continues to be low confidence with the details, locally heavy rains with the potential of 2.5" an hour amounts (particularly across southeast AZ) could be problematic. Urban areas, arroyos/dry washes, box/slot canyons, and burn scars would be most at risk for flash flooding. A Slight Risk from continuity remains across southeast AZ. Roth Day 3 Valid 12Z Thu Aug 13 2026 - 12Z Fri Aug 14 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDWEST, OHIO VALLEY, HIGH PLAINS, & THE SOUTHWEST... Midwest/Ohio Valley... A sharpening upper level trough extending south of a deep layer cyclone in Quebec forces the leading edge of the Westerlies to extend from the Central/Northern Plains through the Ohio Valley into the southern Mid-Atlantic States. Enough moisture, instability, and effective bulk shear should exist for cell organization. Given the moisture available (precipitable water values of 2"+), hourly rain amounts to 3" with local totals to 6" would be possible. Continuity was fairly well maintained in this region. High Plains... Upslope flow behind a front and ahead of a surface low combined with a broadening Western trough leads to increased moisture pooling and instability across the region and leads to minimal, if any, mid-level capping. The guidance brings 1.25-1.75" precipitable water values into portions of eastern MT, eastern WY, and eastern CO which would approach record levels for any time of the year. ML CAPE could rise above 2000 J/kg. There's an antiparallel flow relationship between the low-level upslope and expected convective propagation, which should lead to high precipitation efficiency wherever storms can cluster/have greater coverage. There are a couple areas near the WY/CO/NE border junction and irregular WY/MT/SD/ND border junction where the guidance has higher amounts. Given the favorable ingredients for heavy rainfall, believe the Slight Risk is higher end in those areas. Risk areas were generally maintained from continuity. Hourly rain amounts to 3" with local totals to 6" can't be ruled out where cell stall, backbuild, merge, or train. Intermountain West... A broadening upper level trough brings an increasing south- southwest low-level flow to portions of the region and cooling aloft. Precipitable water values exceed 1" in spots, with 1.5-2" values across southern AZ. Some areas could see ML CAPE rise above 1000 J/kg. Enough effective bulk shear could exist for cell organization/training but it's unclear if enough cell coverage will exist, outside of Southeast AZ. Risk areas were generally maintained from continuity. Hourly rain amounts to 2" are possible where cells train and/or merge. This would be most problematic in burn scars, urban areas, box/slot canyons, and arroyos/dry washes. Roth Day 4 and Day 5 Valid 12Z Fri Aug 14 2026 - 12Z Sun Aug 16 2026 ...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE FRONT RANGES AND PLAINS OF COLORADO AS WELL AS FOR PORTIONS OF THE UPPER MIDWEST ON FRIDAY... ...Colorado and Adjacent Areas... An easterly low level jet branching off of broad southerly flow up the Plains will support a combination of upslope and convective rainfall across much of northern Colorado on Friday. PWATs near the Kansas border will approach 1.75 inches, lowering to around 1 inch into the Rockies behind the Front Range. This ample moisture will funnel north and west ahead of a large upper level trough over the West Coast. Upper level shortwaves will also support more widespread convective development across much of Colorado. A Slight Risk area was introduced for the potential for flooding from these storms, since many of them will be tied to the local terrain, but still being refueled by the easterly low level jet of moisture into the Front Ranges. ...Upper Midwest... A small Slight Risk area was introduced for portions of eastern Iowa, far southeastern Minnesota, southwest Wisconsin, and northwestern Illinois with this update. A strong warm front with PWATs over 2 inches in many areas will support plentiful convection across this region. FFGs in the area are generally around 2 inches per hour, lower in any urban areas. Thus, confidence has increased given these very favorable factors to introduce a Slight at this time. The 00Z EC favors this area for heavier rain, which will ultimately be dependent on how fast the warm front pushes northeastward into Wisconsin. ...Day 5/Saturday... The warm front pushing northeast into Wisconsin will favor continued heavy rainfall into this region from the ongoing storms/MCS that begins Friday. Given how far out this is, have opted to hold at just a Marginal for now, as the track and intensity of MCSs at this range are frequently far off from what ends up happening. That said, the abundant moisture, strong forcing, and low FFGs into Wisconsin would support Slight Risk level impacts. Any southward shift of the heaviest rains may impact the Chicagoland area more significantly, so that will have to be monitored in the coming days. Wegman 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 $$