929 FOUS30 KWBC 292001 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 401 PM EDT Wed Jul 29 2026 Day 1 Valid 16Z Wed Jul 29 2026 - 12Z Thu Jul 30 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE BERKSHIRES AND SURROUNDING AREAS... ...16Z Update... The Moderate Risk was trimmed from the east across central Massachusetts and eastern Connecticut with this update. While rain is ongoing in most of these areas, the area didn't see anywhere near as much rain as areas further west from the Berkshires to the Hudson Valley, so the area remains in a Slight. The Marginal and Slight risk areas were trimmed on the southern end along Long Island Sound (including NYC), as the steadiest rains in that area have ended. Scattered showers can't be ruled out, but even in urban areas should not produce enough rain to cause even isolated flash flooding. Minor tweaks were made to other portions of the Northeast. Out west, the Marginal Risk was extended northwest to include the Missouri River valley in eastern Nebraska and Kansas, as well as western Iowa and Missouri, including the KC Metro. This is primarily for heavy but slow moving storms that have developed in this area from an overnight MCS. Finally, the Slight Risk in Colorado was expanded south to include the extreme northeastern fringe of New Mexico, where afternoon showers and thunderstorms that will be at least initially tied to the terrain may cause widely scattered instances of flash flooding. Wegman ...Previous Discussion... ...Northeast... Intense rainfall will be on-going over portions of the Northeast as the Day 1 period begins at 29/12Z, with some training of cells and some places experiencing multiple rounds of heavy rainfall--particularly across western Massachusetts, far southern Vermont, and broadly across southern New England. Rainfall rates between 1-2"/hr at times will be possible through late morning/early afternoon and totals of 2-4" (with localized higher amounts possible) are expected. HREF/RRFS neighborhood probabilities from the 29/00Z runs remained high (greater than 80 percent) for 3" totals across western/central MA into far southern VT. Probabilities are moderate (30-50 percent) for 5" totals. Given the setup and risk of significant flash flooding continuing from the day 1 period, a Moderate Risk was maintained with few changes given the cumulative rainfall amounts. After 30/00Z...the intensity of rainfall should subside while also shifting eastward. ...Four Corners States into the Central/Northern Plains... Monsoonal flow persists with isolated to widely scattered convection extending from the Four Corners region northward and eastward...perhaps extending as far east as the plains of Colorado. Some of this rain could fall atop soils saturated from heavy rain prior to the start of the Day 1 period at 29/12Z. Persistence in the pattern and moisture distribution leaves the risk area in good shape with the Slight Risk focused on eastern Colorado. ...Central Gulf Coast Region into parts of the Southeast... A cold front stalling along the Gulf Coast will be a focus for slow moving and training thunderstorms today into tonight. Guidance continues to indicate a low-probability threat for at least 3" of rain due to training of 1-2"/hr rain rates within favorable thermodynamics. This region can generally tolerate significant rain rates and this amount of rainfall, but any more pronounced training could result in isolated flash flood related impacts. Taylor/Bann Day 2 Valid 12Z Thu Jul 30 2026 - 12Z Fri Jul 31 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID TO LOWER MISSOURI AND MID TO UPPER MISSISSIPPI VALLEYS... ...2030Z Update... No major changes were needed with this afternoon's update. The Slight Risk over the Plains and Midwest was expanded westward with the latest update due to guidance moving the area of heaviest rainfall westward as compared to prior forecasts. Otherwise, few changes were needed. The heaviest rains through the period continue to be forecast from northeastern Nebraska through southwestern Minnesota. Storm coverage and intensity across the 4 Corners region appears significantly muted as compared with previous days. The Marginal Risk in the area was trimmed back to portions of Arizona and New Mexico as a result. A moisture feed from the Gulf will allow for a few storms to form over western Arkansas and into the Lower Mississippi Valley. The Marginal Risks were combined along the front. Lingering moisture along the New England coast could continue to pose an isolated flash flooding threat, so the Marginal was maintained and expanded a bit over southeastern Massachusetts, Rhode Island, and eastern Connecticut. Wegman ...Previous Discussion... ...Lower Missouri Valley into the Mid-Upper Mississippi Valley... Shortwave energy will be progressing east southeast as it tracks across parts of the central and northern plains on Thursday into Thursday night/early Friday morning. The shortwave energy will be encountering an increasingly moist and unstable airmass with precipitable water values in excess of 2 inches being drawn into the region ahead of the shortwave. Given the MCS/upscale growth potential with this system, concentrated areas of heavy rain are expected given the potential for training and repeat-convection. The Slight Risk remained in good shape and only minor adjustments were needed to covers the 29/00Z ensemble guidance and to account for the uncertainty/spread among the models. ...Four Corners States into the Central/Northern Plains... Monsoonal flow and anomalous deep-layer moisture will maintain an isolated excessive rainfall risk extending from eastern Arizona northeastward across much of western and northern New Mexico into parts of Colorado. The expanding mid/upper level ridge will likely limit the coverage compared to recent days. ...Central Gulf Coast Region into parts of the Southeast... Heavy rainfall is expected along a front associated with a low pressure system which will be pulling away from New England. Heavy rainfall with some potential of flooding will be focused along and near the front...especially over parts of Florida and Georgia near the state line. ...New England... The departing low pressure is expected to be across eastern MA at the start of the period and transition off the coast during the period. Locally heavy rainfall will remain possible across the region given its proximity and ample moisture to work with. While the instability will likely be less compared to Tuesday/Wednesday, the stronger dynamics at play and potential for training rainfall could lead to a localized threat, particularly if over areas more saturated from previous rainfall. A Marginal Risk was maintained. Taylor/Bann Day 3 Valid 12Z Fri Jul 31 2026 - 12Z Sat Aug 01 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FRIDAY ACROSS PARTS OF THE UPPER MIDWEST TO MID MISSISSIPPI VALLEY... ...2030Z Update... A small increase in coverage of heavy rain across the Mid- Mississippi Valley led to a small expansion of the Slight to cover portions of eastern Missouri and western Kentucky with this update. The heaviest rains continue to be focused into far eastern Iowa, northwestern Illinois and southwestern Wisconsin, where no changes were made as the forecast remains on track. Elsewhere, some small adjustments of the MRGL to remove portions of northwestern New Mexico and include more of the Texas Panhandle were made, but total coverage and intensity of storms in these areas remains little changed. Wegman ...Previous Discussion... Central US system... Shortwave energy initially moving eastward out of the Northern Rockies and adjacent High Plains will be accompanied by showers and thunderstorms on Friday morning. The flow pattern on the northern part of the upper high anchored to its west sharpens during the day...which induces a turn to the south for the northern Plains system. Tended to follow the numerical guidance for placement of the Marginal and Slight risk areas where the synoptic scale forcing is greatest. This necessitated a bit more eastward nudging from the previous outlook. The southern portion of the Marginal risk area remained closer to the placement of greater instability which would support higher intensity rainfall rates. Any downpours across that region may at least have a chance at challenging the flash flood guidance. Both the GFS and ECMWF placed their axis of highest precipitable water (1.8 to 2.2 inches) near the Mississippi River early in the period which gets deflected towards the Tennessee Valley by early Saturday morning. ...Central Gulf Coast Region into parts of the Southeast... Locally heavy to excessive rainfall is possible in proximity to an east-west oriented quasi-stationary front that had been associated with a Northeast US cyclone in previous days. Deep-layer moisture and instability should be more than sufficient and the guidance shows sufficient effective bulk shear (0-6km magnitudes generally over 20 kts) for more organized/persistent convective organization. As a result, maintained the inherited Marginal Risk . ...Four Corners States into the Southern-Central High Plains... Monsoonal flow and anomalous deep-layer moisture will keep the potential for isolated instances of excessive rainfall across portions of eastern AZ and much of New Mexico into Colorado. The areal coverage may be less than in preceding days given the expansion of the sprawling upper ridge. Bann Day 4 and Day 5 Valid 12Z Sat Aug 01 2026 - 12Z Mon Aug 03 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL SATURDAY OVER PORTIONS OF THE OHIO AND TENNESSEE VALLEYS... 2030Z Update... Extended the Day 4 Slight Risk farther south from the Ohio into the Tennessee Valley. Storms are expected to develop ahead of the cold front associated with the shortwave trough moving through the Midwest on Saturday. The model spread with regards to where the better forcing will focus and its potential impact on the development of heavier amounts is notable. However, the 12Z guidance presented enough of a signal to warrant extending the Slight Risk farther south. Storms that develop in this area will have access to deeper moisture (PWs ~2-2.25 inches) and likely greater instability, supporting heavy rates. Elsewhere, made only minor adjustments to outlook areas on both days. Pereira ...Ohio and Tennessee Valleys into parts of the Southeast... On Day 4 (Sat-Sat night), rather significant changes were made to yesterday's Day 5 ERO, based on the latest guidance trends. Specifically, the globals and most ensembles show the upper trough amplifying somewhat with the influx of shortwave energy/convectively- aided vort lobes dropping southeast. However, most of the guidance show less amplification compared to last night's runs, with more of a positive to neutral tilt to the trough vs. negative. This in turn is allowing for a more progressive west-to-east shift in the pre- frontal rainfall east of the Mississippi, supported (perhaps led by) both the GFS and ECMWF AI models. Therefore the Marginal Risk and encompassing Slight Risk areas were shifted east as well, with the Slight Risk confined to mainly the northern areas (OH Valley into Cumberland Plateau) per the ECMWF and GFS AI trends, along with the highest 24hr QPF exceedance probabilities per the 00Z ECENS, and where there is a signal (albeit weak) per the most recent ECMWF EFI. The Slight Risk is also in an area with comparatively lower 1/3/6 hr FFG vs. areas farther south. ...Interior Northeast... Aforementioned longwave 500 mb trough does begin to take on a more neutral to negative tilt on Day 5 (Sun-Sun night) per both the GFS and ECMWF. As this occurs, the eastward progression of the favorable pre-trough/front dynamical forcing and associated moisture axis (PWs of 1.75-2.00") will begin to slow considerably, thereby allowing for multiple rounds of moderate-heavy rainfall. For now, have hoisted a Marginal Risk across this region on Day 5, as the maximum 24hr deterministic QPFs from the latest global runs are still (for the time being) under 3". ...Four Corners States into the Southern-Central High Plains... Monsoonal flow and anomalous deep-layer moisture will maintain a Marginal (isolated) excessive rainfall risk over eastern AZ and much of NM into south-central CO on Day 4. By Day 5 (Sun-Sun night), both the deterministic and probabilistic QPFs per the global and AI guidance would support a smaller MGNL Risk area. ...Central Gulf Coast Region into parts of the Southeast... Heavy rainfall threat will continue over this region along the southern periphery of the full-latitude trough, south of the quasi-sationary front. Deep-layer moisture and instability should be more than sufficient, especially when coinciding with the weak upper forcing (upstream upper trough w/ embedded convectively-aided shortwaves), for more organized/persistent convective organization. As a result, have maintained the inherited Marginal Risk on Day 4 (Sat-Sat night), with a similar Marginal Risk area on Day 5 (Sun-Sun night). Hurley 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 $$