756 FOUS30 KWBC 022026 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 426 PM EDT Thu Jul 2 2026 Day 1 Valid 16Z 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... ...16Z Update... Relatively few changes were needed to the inherited forecast across the country for today. MCS development, likely in the form of multiple clusters of storms, are expected to impact many of the same areas currently being hit with heavy rain from southeastern Minnesota and into Wisconsin. It's likely there will be a small southward adjustment as to where the heaviest rainfall occurs this afternoon into tonight as compared to where the heaviest rains are occurring, thus highlighting much of the northern tier of counties in Iowa, but the "leftovers" from those storms should include residual lighter rainfall into southeastern Minnesota as well, so a new higher-end Slight was introduced with this update for north/northeastern Iowa, south/southeastern corner of Minnesota, and far southwestern Wisconsin. A new Marginal Risk area was introduced for portions of south Florida, to include Miami, Fort Myers, and the southern suburbs of Tampa. Typical afternoon and evening thunderstorms will develop once again this afternoon. These storms are most likely to remain more over the interior of Florida than those aforementioned coastal cities, however sea breeze interactions and cold pools could allow those storms to develop over those urban areas, where the primary flash flooding threat exists, necessitating the issuance of the Marginal. For portions of the southern High Plains, the Marginal Risk remains unchanged, highlighting isolated to widely scattered convection along the dry line that could move over flood sensitive areas, particularly near the Big Bend of West Texas. Any convection is unlikely to move too far from the dry line. Wegman ...Previous Discussion... ...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 FOR MUCH OF IOWA AND EASTERN NEBRASKA... ...2030Z Update... Guidance has shifted notably south and west for the Day 2/Friday period regarding where the heaviest rains are expected for the period. Expect a dying overnight MCS to impact much of central and eastern Iowa Friday morning, followed by renewed MCS development Friday night starting in eastern Nebraska and continuing into southern Iowa. The combination of these two areas of rain, with a notable break in between, led to the shifting of the Slight south and west of the inherited area, and the trimming of the Slight out of areas east of the Mississippi River. Much of northern Iowa will have seen 2 days of MCS's capable of producing heavy rainfall, so the south and west shift of the heaviest rains is good news both that the most intense areas of rain hit much drier areas soils- wise, and that the hard hit areas of the state get lighter rainfall over a longer time as outflow from the MCS' much heavier rainfall to the south and west. The heaviest rains for the day by far will come from a developing MCS Friday evening through Friday night across eastern Nebraska that tracks southeastward into south-central Iowa. It's in this corridor that the more significant localized flash flooding could occur, due to much heavier hourly rainfall rates. Showers and storms will develop east from there through Chicagoland and along Michigan's southern border through the day, but short residence times of the heavy rainfall due to sufficiently fast movement of the storms should keep any flash flooding risk in these areas isolated and consistent with a Marginal Risk. For southeast Florida, it will be a rinse and repeat scenario regarding afternoon convection blossoming across the middle of the state south of Lake Okeechobee, then slowly drifting east towards the urban corridor from West Palm Beach south, where any isolated flash flooding threat exists. A small Marginal Risk area was introduced with this update. Wegman ...Previous Discussion... 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 AND TENNESSEE VALLEYS, AND MID-ATLANTIC... ...2030Z Update... Happy 250th Independence Day! A continued expansion of the Marginal into portions of the Tennessee Valley as well as across New Jersey and through the New York City Metro was introduced with this update. This is in part due to the high humidity and heat fueling stronger thunderstorms in this area, increasing the flooding risk, as well as for the much higher impacts any of those storms could have to the many Independence Day festivities Saturday evening. As is typical with summertime convection, the signals remain sparse for heavy rainfall, so only a Marginal Risk was left for this update. It's likely that CAMs data in future updates will greatly help narrow down any areas where Slight Risk level impacts can be expected. Two areas stand out for greater potential for heavy rainfall within this large Marginal Risk area: the upper Midwest and central Plains. For the upper Midwest, any Slight Risk level impacts would likely be tied to whether the forecast rain associated with a low and attendant cold front moving across the area can shift south with time and better model resolution towards areas harder hit with heavy rain across southeast Minnesota and central Wisconsin. The other is from southeast Nebraska through the Kansas City metro, where a Saturday evening and overnight MCS that likely develops in southeastern Nebraska and northeast Kansas around fireworks time at sunset then advects southeastward into the Kansas City metro after midnight. There is significant variability in the guidance as to the location and timing of this MCS, though the broader area has generally been little-changing. Urban impacts still appear the most pressing concern, and the potential the MCS will be moving quickly and impact the Kansas City metro after midnight when most Independence Day festivities are over could reduce the impact such that a Marginal remains the best risk type for now. Additional updates are likely for Saturday as the weather picture becomes clearer. Wegman ...Previous Discussion... 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 SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID-ATLANTIC... 20z Update: We upgraded portions of the Mid-Atlantic to a Slight risk on both days 4 and 5 as a favorable synoptic setup for heavy rainfall persists across the region. A low to mid level trough interacting with a backdoor front should provide a focus for heavy rainfall Sunday into Monday. At least moderate levels of instability should overlap with PWs over 2" across portions of the region. While the overall heavy rainfall signal is robust enough to warrant a Slight risk upgrade, considerable spatial uncertainty remains regarding the exact axis of the flash flood threat. For now the Slight risk aligns near the expected backdoor front location where the overlap of forcing, high PWs and instability should be maximized. However, adjustments to this risk area are likely over the coming days as confidence increases and model guidance comes into better agreement on the positioning of the boundary and stronger forcing. Chenard ...Previous Discussion... 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 $$