FOUS30 KWBC 252356 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 756 PM EDT Sat Jul 25 2026 Day 1 Valid 01Z Sun Jul 26 2026 - 12Z Sun Jul 26 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE SAVANNAH RIVER VALLEY AND SOUTHWEST... ...Southeast through the Lower Mississippi and Tennessee Valleys... Deep moisture will continue to pool along and near a stalled frontal boundary, has led to extensive moisture from the southern Appalachians across SC. A couple rounds of heavy rainfall are expected -- one early across SC and one later on in and near the Southern Appalachians over lower flash flood guidance/more rugged terrain -- led to a rearrangement of the Slight Risk area across the region. Hourly amounts to 2.5" can't be ruled out. Scattered thunderstorms across Florida early, and then near the Southwest coast and Keys late, could also cause localized heavy rain. Reconfigured the Marginal Risk area somewhat to account for the 18z HREF/12z REFS probabilities in this area. ...Southwest... Monsoonal moisture/instability has led to convection across the region this afternoon. An MCV in the vicinity still appears to be a key player in enhancing the rainfall which leads to greater/higher rain rates. Based on radar reflectivity/HREF and REFS probabilities of 0.5"+ through 12z, some reductions were made to the Marginal and Slight Risk areas across CO and NM while the Marginal Risk area was expanded into the Lower Deserts/towards the Lower CO River where an outflow boundary and some preceding convection could lead to cell mergers early this evening. ...South Dakota... Convection across the state hasn't shown much alignment as of yet, but there is some risk for repeat convection in the near term based on recent radar reflectivity data. The region has been dry, so left out any risk areas for the time being. Isolated flash flooding can't be ruled out completely if cells manage to train/align. Roth Day 2 Valid 12Z Sun Jul 26 2026 - 12Z Mon Jul 27 2026 ...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL ACROSS THE FOUR CORNERS REGION...MIDWEST...AND PORTIONS OF THE SOUTHEAST/FLORIDA... ...Four Corners States onto the Central Plains... Monsoonal flow from the Desert Southwest to the central Rockies continues into early next week. Above average precipitable water values and available instability will again support isolated to widely scattered thunderstorms capable of producing intense rain rates capable of producing flash flooding. There may be a general focus for moisture/instability axis to extend farther north than Saturday, and there is some signal in the CAMs and global guidance to focus the greatest coverage of heavy rain into western/central Colorado. Will hold off on any Slight Risk upgrade though due to uncertainties in the impacts, as well as uncertainties with instability after an active monsoon Saturday. ...Upper Midwest-Upper Great Lakes-Ohio Valley... Global, CAM, and AI guidance continue to show convectively-aided shortwave activity riding down the top side of the upper ridge axis in northwest flow. A northwest to southeast oriented stationary front could also provide a convective focus as slightly above normal PWs but very strong instability come in. However, models show quite a bit of spread in position of these ridge riders especially for a short range forecast. The location of convection will be affected by placement of upper level convergence associated with a broad arching anticyclonic flow at the jet level. Adjusted the Marginal Risk to fit with a middle ground model "consensus," but it does not cover all the CAM and global model scenarios, so may need to be adjusted further. Fast movement will be a mitigating factor for flooding though. ...Southeast into Florida... Above average moisture will continue to flow into the southeastern U.S. into a quasi-stationary front with possible waves of low pressure stretching across Georgia and South Carolina at the base of an eastern U.S. trough. This front and a surface trough across Florida should focus the moisture for convection. 90+ percentile PWs are present along the eastern coast of Florida, where urban corridors can increase sensitivity to high rainfall rates. A Marginal Risk covers the threat of isolated flash flooding with this activity. Tate/Bann Day 3 Valid 12Z Mon Jul 27 2026 - 12Z Tue Jul 28 2026 ...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL MONDAY ACROSS THE FOUR CORNERS STATES TO CENTRAL PLAINS AND GREAT LAKES/OHIO VALLEY... ...Four Corners States into the Central Plains... Elevated amounts of moisture will linger over the Four Corners region given a persistent monsoon pattern, although guidance still points to a gradual southward shift in the placement of the upper high center. This may slightly reduce thunderstorm coverage in areas like Utah to the Four Corners themselves, but a weak shortwave looks to move across Colorado and vicinity Monday into Monday night and enhance convection there and spreading into the central Plains overnight. Maintained a Marginal Risk area in the Four Corners states and extending eastward into the central High Plains to cover the isolated flash flooding threat. Plots of ECMWF PW anomaly plots continue to prove helpful in highlighting areas of increased concern. ...Great Lakes and Ohio Valley into the Northeast US... By Monday a more potent shortwave will move southeastward through the Upper Great Lakes region rounding the Rockies/High Plains high. Difluent flow ahead of the shortwave will eventually lead to the consolidation/strengthening of a low pressure system during the period. This low is expected to help forcing for heavier rainfall over the Great Lakes/Ohio Valley, with less model spread than the Sunday convection likely due to greater forcing. A Marginal Risk remains in place, but convective activity should be relatively progressive, which is still expected to mitigate any higher risks of excessive rainfall. Tate/Bann Day 4 and Day 5 Valid 12Z Tue Jul 28 2026 - 12Z Thu Jul 30 2026 ...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF THE WEST, PLAINS, & EAST... ...Four Corners States into the Central/Northern Plains... Monsoonal flow, likely to be enhanced by Genevieve moving offshore Baja California, brings elevated moisture over the Desert Southwest through the central Rockies and into the central and northern Plains. The more suppressed ridge will allow multiple mesoscale/convectively aided shortwaves to push over the top/across the Rockies into the Plains. ...Central Appalachians-Mid Atlantic through New England... Upper level jet streak riding down the northeast side of a warm core ridge on Tuesday will lead to amplification of the longwave trough across the Eastern U.S. by the middle-later part of next week, leading to a deep layer, eventually coastal, low. Whenever favorable (typical) warm- season thermodynamics (deep- layer instability and moisture) are present ahead of a more robust, cooler-season trough with strong deep- layer shear, chances for more widespread convection are much higher. Though a Slight Risk was contemplated from eastern Long Island through southern New England as far north as Portland ME where a few pieces of guidance advertise 2-4" on day 5/Wednesday into Wednesday night, coordination with the local forecast offices maintained the Marginal Risk from continuity. Sooner or later, a Slight Risk will probably be needed, especially once the event moves into the high res (CAM) windows and the QPF signal becomes less variable and more robust. ...Southeast... Heavy rainfall is expected along the New England cyclone's trailing front near the FL/GA border. Moisture should be ample and there could be enough effective bulk shear for convective organization. Since to some signal seen in the model guidance in this region, added a Marginal Risk area. Roth 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 $$