FOUS30 KWBC 252057 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 457 PM EDT Sat Jul 25 2026 Day 1 Valid 16Z Sat Jul 25 2026 - 12Z Sun Jul 26 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE EASTERN CAROLINAS AND THE SOUTHWEST... ...Southeast through the Lower Mississippi and Tennessee Valleys... Deep moisture will continue to pool along and near a stalled frontal boundary, which leads to precipitable water values reaching nearly 3 standardized anomalies above climatology for late July and in excess of the 95th percentile of climatology extending eastward from the Lower Mississippi and Tennessee Valleys to the Carolinas. Recent CAMs continue to point to heavy rainfall potential, with localized 2-4 inch totals with higher instantaneous rainfall rates, especially in the eastern Carolinas where the Slight Risk remains. Refer to MPD 846 for more on the threat into this afternoon. Trimmed off the northern side of the Slight given less instability to the north of the front in this issuance. However, did expand the Marginal northward a bit farther west to cover the southern Appalachians, where localized convection could be present this evening and tonight over areas with wetter antecedent conditions and lower FFG. Farther west, recent guidance remains less enthusiastic compared to a day ago regarding heavy rainfall in and around Arkansas. With the 00Z and 12Z CAM/HREF cycles both laying off on heavy rain, felt confident enough to remove the Slight Risk there. The 12Z HREF does show some 30-40 percent probabilities of QPF exceeding FFG near the Mississippi/western Tennessee border that could be a relatively higher risk, but with too low confidence in impacts to upgrade to a Slight there. Scattered thunderstorms across Florida could also cause localized heavy rain, but currently consider that to be sub-Marginal as EAS probabilities of exceeding 2 inches is only around 10 percent, and over the Everglades rather than the more sensitive urban corridor. ...Southwest... The monsoon will get re-invigorated across the Four Corners today with an uptick in coverage and intensity of rainfall expected in the region. Instability could be 1000-2000 J/kg while precipitable water values are forecast to be above the 90th percentile. An MCV in the vicinity could become a key player in enhancing the rainfall which leads to greater/higher rain rates. Concern is heightened given the possibility that the higher rainfall rates/amounts overlaps with areas which have recently dealt with heavy rainfall and where soils will be less capable of handling the influx of rain water. The Marginal and Slight Risks still look on track and were adjusted only minimally from the previous issuance. Tate/Bann 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 $$