799 FOUS30 KWBC 302012 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 412 PM EDT Thu Jul 30 2026 Day 1 Valid 16Z 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... ...16z Update... The day 1 outlook areas remain mostly the same with some minor adjustments. The latest 12z hi-res guidance has trended higher with QPF amounts over portions of the Northern Plains/Upper Midwest. A squall line is still expected to develop over southern/central South Dakota and propagate east-southeastward. Precipitable water percentiles are expected to be at a maximum (2"+) and instability between 2000-3000 J/Kg over these areas, which should support an enhanced slight risk area for portions of eastern South Dakota, northeastern Nebraska, southwestern Minnesota and far northwestern Iowa. Kebede ...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 today into 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 ahead of the shortwave. Model guidance still reflected an increased risk for excessive rainfall over portions of Arkansas and the outlook area was largely left unchanged in this cycle. 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. ...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 during the afternoon and evening hours. ...New England... A low pressure system located along the southern New England coast at the start of the outlook period will take a turn to the northeast and head out to sea later today. 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. Bann Day 2 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... The inherited slight risk was expanded into central Iowa/Missouri and the Chicago Metro area based on the latest hi-res trends. Moisture (2"+ & 99th+ percentile PWATs) will be sufficient enough to produce efficient rain rates, however, higher instability may not make its way far enough north to help realize higher rates. Flash flood guidance around 1" will allow for any convection/heavy rainfall to potentially produce flash flooding. The marginal in the Southwest remains unchanged, however diurnal monsoonal convection that develops over northeastern New Mexico is expected to dive south and generate isolated to scattered flash flooding in eastern portions of the state. Kebede ...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 as the Day 2 period begins at 12Z on Friday. The system will start taking a southward track in response to upscale ridging across Montana and nearby areas of southern Canada. The placement of the Marginal and Slight risk areas were similar to the previous outlook and saw little reason to stray far from the adjustments that were made on Wednesday because there was still good agreement with where the synoptic scale forcing will be greatest. 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. ...Central Gulf Coast Region into parts of the Southeast... Locally heavy to excessive rainfall remains possible along and near an east to west oriented quasi-stationary front. 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, no changes to the Marginal Risk area already issued. ...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 3 Valid 12Z Sat Aug 01 2026 - 12Z Sun Aug 02 2026 ..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE OHIO/TENNESSEE VALLEYS and eastern New Mexico... ...2030z Update... ...Ohio/Tennessee Valley... The slight risk over the Ohio Valley was expanded west into eastern Illinois to account for increasing QPF trends in both the deterministic GFS and Euro. A potent mid-latitude cyclone is still on track to supply ample instability into the Midwest on Saturday night, beneath a deepening positively tilted mid-level low. Storms will propagate from the Upper Midwest on Saturday into the Ohio/Tennessee Valleys on Sunday amidst this strengthening system aloft. ...New Mexico... The slight risk in New Mexico is maintained but shifted south a bit based on the latest model guidance. North-to-south storm motion within an increasingly moist environment (1"+ and 97.5th percentile PWATs) and relatively saturated soils from Friday storms will contribute to the flash flooding threat. Kebede ...Previous Discussion... ...Ohio and Tennesee Valleys To Parts of the Southeast US... The transport of moisture northward from the Gulf will only increase on Saturday ahead of an amplifying mid- and upper-level trough approaches from the west. This sets up the possibility for heavy to excessive rainfall from parts of the Ohio and Tennessee Valley and southward into the Southeast states from Saturday to early Sunday morning. The spread in model deterministic QPF and from the ensemble neighborhood probability of exceedance plots remained large...which seemingly led to only modest QPF amounts in blended QPF solutions. With the mid-level wave approaching 2 standardized anomalies and the precipitable water still forecast to be in the 2 to 2.25 inches range...think there is more potential for heavy rainfall than not. Expanded the Slight Risk area southward but not to the point where the 1- and 3-hour flash flood guidance exceeds 4 inches per 3 hours. ...Four Corners States into the Southern-Central High Plains... Monsoonal flow and anomalous deep-layer moisture will persist over much of the Four Corners region and adjacent areas. Once again...WPC maintained a Marginal excessive rainfall area here without much change in coverage due to forecast reasoning remaining the same. ...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. Bann Day 4 and Day 5 Valid 12Z Sun Aug 02 2026 - 12Z Tue Aug 04 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER EASTERN PORTIONS OF THE UPPER GREAT LAKES AND THE UPPER OHIO VALLEY... 2030Z Update... Following the general trend shown by several 12Z runs toward a more quickly-amplifying, slower solution, shifted the outlook areas farther west -- centering the Slight Risk more over the lower Great Lake/upper Ohio Valley region and extending it back into southeastern Lower Michigan. Also added a Marginal Risk to parts of the eastern Gulf Coast on both days. A deep moisture pool (PWs 2.25-2.5+ inches) ahead of a low level boundary will support storms capable of producing highly-efficient rainfall rates and heavy amounts. The greater threat for heavy rainfall is expected to extend across the Florida Panhandle into North Florida on Day 4, with the threat waning on the western edge on Day 5 as the boundary and axis of deepest moisture slowly drifts east. Pereira Previous Discussion... An axis of anomalous PW likely along and ahead of the cold front expected to push out of the eastern Lakes into the northeast in the Sunday to Monday time frame. There is the beginning of model divergence with the evolution of the upper trof and the details of how the trof splits into northern and southern components, affecting the timing in the models with the eastward push of the front and the associated precip. However, overall favorable upper dynamics in the anomalous PW axis should support active convection along and ahead of this front, with potential for a period of training in the moist low level southwest flow parallel to the front. A slight risk was introduced for heavy rain potential that may fall across areas with reduced FFG values from the recent very heavy rainfall amounts from northeast PA into northern NY State. For both day 4 and day 5...a marginal risk was depicted for monsoonal convection across southern Arizona into southwest New Mexico. Not a lot of confidence with qpf details here, but locally heavy rains and isolated runoff issues possible in the above average PW values expected across this area. By day 5...there are more significant model differences with the evolution of the upper trof across large portions of the east. The GFS is keeping the southern component of this trof stronger and farther north than much of the other guidance and has a more significant heavy rain foot print from NC into southern New England. While confidence is low with any one solution, there is still potential for heavy precip in the anomalous PW axis that will continue ahead of this upper trof. Some of this may fall across portions of southern New England and the northern Mid- Atlantic that have lowered FFG values from recent heavy rains. However, given the low confidence in the mid to upper level trof evolution, at this time range, only a marginal risk is depicted from central NC, northeastward through the coastal Mid-Atlantic into southern NY State and southern New England. Oravec 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 $$