504 FOUS30 KWBC 020830 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 430 AM EDT Thu Jul 2 2026 Day 1 Valid 12Z Thu Jul 02 2026 - 12Z Fri Jul 03 2026 ..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHERN PLAINS AND UPPER MIDWEST... ...Northern Plains to Upper Midwest... A familiar pattern remains in place within the mean flow along the northwestern side of the upper-high over the eastern U.S. as yet another round of storms is expected through the northern Plains into the Upper Midwest. Daytime heating and plentiful moisture (PWATS 1.5-2") pooling along a quasi-stationary boundary draped from the central Dakotas southeastward through southern Minnesota and into northern Wisconsin will support ML CAPE in the 3000-4000 J/Kg range. A favorably timed upper-wave embedded in the flow will help lead to storm development along/south of the boundary. One focus region will likely be at the leading edge of moisture advecting northwestward through the central Dakotas ahead of surface troughing along the High Plains. The latest runs of the hi-res guidance suggest the potential for storms to organize/grow upscale into an MCS and move southeastward along the boundary. Storm motions generally parallel to the boundary will encourage repeated rounds of storms both with any additional development ahead of this MCS as well as with potential backbuilding of storms along the trailing outflow. The hi-res guidance shows heavy rain rates of 1-2" per hour with the prolonged storm duration leading to locally heavy rainfall totals of 3-5", sufficient to cause scattered instances of flash flooding. ...Southern High Plains... Additional thunderstorms are expected today ahead of a dryline through the southern High Plains. Storm development is most likely east of the higher terrain through southwest Texas. Weak upper- level shear and high storm bases will likely limit storm duration but lingering seasonably high moisture in place (PWATs 1-2 standard deviations above the mean) will contribute to heavy downpours with 2"+ totals possible. Further north, most of the hi-res guidance is less bullish on the potential for additional storms, though a similar potential for heavy downpours will exist with any storms that do develop. Putnam Day 2 Valid 12Z Fri Jul 03 2026 - 12Z Sat Jul 04 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE UPPER MIDWEST TO THE WESTERN GREAT LAKES REGION... A similar pattern to day 1 (Thursday) will once again be in place on Friday as the quasi-stationary frontal boundary remains draped through the Upper Midwest under faster mean flow rounding the eastern upper-ridge. Embedded upper-wave(s) will help to encourage storm development with daytime heating. Seasonably high moisture (PWATs 1.5-2") and instability (ML CAPE 3000-4000 J/KG) will also continue to support robust storms capable of heavy downpours with now-available hi-res guidance supporting locally heavy totals of 3-5". While the environment will remain primed for this additional rainfall, there is greater uncertainty as to the exact location/coverage of storms. Outflow from a potential MCS during the day 1 period will help determine the location of the frontal boundary on Friday. The hi-res guidance available through the day 2 period not surprisingly suggests the boundary will be further south of where the global guidance depicts the corridor of heavier rainfall. The inherited Slight Risk was adjusted following a more east-west orientation that brought the eastern half of the risk area south from central Wisconsin to include southern Wisconsin and far northern Illinois. Additional southward adjustment may be needed if these guidance trends hold but for now this at least helps to orient the risk more similar to the east-west boundary position/corridor of heavy rainfall suggested by the hi-res guidance while still including the coverage of heaviest QPF in the global guidance. Putnam Day 3 Valid 12Z Sat Jul 04 2026 - 12Z Sun Jul 05 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL STRETCHING FROM THE NORTHERN/CENTRAL PLAINS THROUGH THE MIDWEST, OHIO VALLEY, AND MID-ATLANTIC... An expansion of heavy rainfall potential and an at least isolated flash flood threat is likely on Saturday as the upper-ridge over the eastern U.S. begins to weaken. This will bring the mean flow and thunderstorm potential further south across the Plains/Midwest and into the Ohio Valley and Mid-Atlantic regions. High moisture and instability will remain in place along the northern side of the ridge south of the frontal boundary with at least scattered thunderstorms likely with daytime heating. The potential for greater coverage of heavier rainfall, higher totals, and more scattered instances of flash flooding is greatest over the northern/central Plains into the Upper Midwest where embedded upper-wave(s) will help to encourage more widespread thunderstorms and the possibility of more organized convective systems. However, given the likelihood of storm outflow influencing the location of the frontal boundary during both the day 1 and day 2 period, there is too much uncertainty to include a more focused corridor of higher probabilities at this time. Putnam Day 4 and Day 5 Valid 12Z Sun Jul 05 2026 - 12Z Tue Jul 07 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL STRETCHING FROM THE LOWER GREAT LAKES EAST PARTS OF THE NORTHEAST AND SOUTH INTO PARTS OF THE MID MISSISSIPPI VALLEY... Upper level winds become more westerly across the northern portion of the central United States build in the wake of a departing upper level trough. That progression should lead to increasing chances for showers and thunderstorms shifting from the Lower Great Lakes and Mid-Mississippi Valley eastward to portions of the Northeast United States and the Mid- Atlantic region. Precipitable water values from 1.5 inches to in excess of 2 inches will be in place in advance of the front. That will support locally intense rainfall rates for convection that does form...even if the confidence remains low in the QPF details. Also a consideration that the increasingly westerly flow will become aligned with a low level boundary making its way southward...opening up the potential for training of cells. The bread marginal risk areas were drawn to encompass the model qpf spread, which is fairly large at this time range. Bann 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 $$