FOUS30 KWBC 060823 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 423 AM EDT Mon Jul 6 2026 Day 1 Valid 12Z Mon Jul 06 2026 - 12Z Tue Jul 07 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF COASTAL NEW JERSEY TO SOUTHEAST Massachusetts... ...Mid-Atlantic and Northeast... Waves of low pressure ripple along a latitudinally wavering stationary front causing multiple rounds of training thunderstorms. During this period the front will likely be sprawled from central Ohio to central New Jersey. Two distinct shortwaves moving along this front will help track dual waves of low pressure eastward, each of which will locally enhance ascent (one across western Pennsylvania, the second from New Jersey into southern New England). Broad areas of ascent, instability with PW values exceeding 2" will be aligned near this front to yield a significant risk for heavy rainfall capable of producing flash flooding. The latest guidance mainly focuses the heaviest QPF over southern New England and portions of northern/coastal New jersey. Although the placement widely varies among the hires guidance there continues to be consensus for areal averages of 3 to 6 inches with local maximums of 8+ as reflected by the REFS and HREF PMM. The neighborhood probabilities reach above 40% for coastal New England and Long Island for 3"/24 hr and 15% for 5"/24 hr. Rainfall rates at times reaching 2-3"/hr combined with aligned mean wind/Corfidi vectors which are parallel to the boundary will drive training/backbuilding to support these heavy rainfall amounts. A Moderate Risk cover far northeast New Jersey, Southeast New York and Long Island, southern Connecticut, southern Rhode Island and portions of southeast Massachusetts. A bit farther west, a secondary area of low pressure interacting with the same thermodynamic environment will produce streaks of heavy rain producing convection from western Pennsylvania through the vicinity of Washington, D.C. While uncertainty is a little higher in this area as to the coverage, speed, and intensity of the thunderstorms, both the HREF and REFS depict a 20-40% chance of 2"/hr rain rates with at least short-term training potential. FFG across western PA is quite low (1-1.5"/3hrs) and HREF/REFS exceedance potential is elevated as a result. Farther south into the D.C. area, FFG is higher, but these intense rates atop more urban regions could still pose a flash flood concern so a Slight Risk was maintained. ...ArkLaTex east through the Carolinas... A slow moving cold front will drop slowly southward, reaching a line from southern Arkansas through eastern Tennessee by Tuesday morning before stalling. This front will sit within a plume of overlapping elevated PWs (1.75 to 2.00 inches) and MUCAPE (1000-2000 J/kg) to support hourly rainfall of 1-2" with higher short-term rates. 0-6km bulk shear is progged to be minimal (less than 20 kts) so storms that form will likely be of the pulse variety. Repeating rounds and possible training of heavy rainfall will keep an elevated threat for flash flooding. A Marginal Risk was maintained. ...Florida... Diurnal heating and onshore flow will help trigger convection along the eastern coastline of Florida with 1 to 3 inches and isolated local maximums up to 5-6 inches. A Marginal Risk area was raised for this period. Weiss/Campbell Day 2 Valid 12Z Tue Jul 07 2026 - 12Z Wed Jul 08 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN PLAINS... ...Northern Plains... During this period a shortwave rounding the ridge anchored over the Four Corners will make its way through central Montana to western Minnesota. This shortwave will drive downstream PVA and height falls while concurrent but modest RRQ diffluence in the tail of a distant jet streak helps enhance synoptic lift. At the surface, a wavering boundary with a wave of low pressure moving along it will try to shift north in response to subtly increasing southerly low- level flow, with the resulting isentropic ascent aiding lift across the region. This robust ascent will act upon PWs that will surge to 1.25 to 1.75 inches, or around +2 sigma, collocated with a plume of MUCAPE exceeding 2000 J/kg. Areal coverage of convection will increase through the day, tracking from west to east. The environment will be favorable for backbuilding or training. Hourly rainfall as much as 0.75"-1.0"+ is likely, which could create locally 2-3" of rainfall as reflected by modest (5-15% chance) of 3"/24 hrs. Soils across this part of the country have been recently wet thus increasing sensitivity. A Slight Risk remains in effect from the eastern Dakotas to western Wisconsin. A broad Marginal Risk extends from eastern Montana to north-central Wisconsin. ...Mid-Atlantic States... Much of this region will continue to have scattered to widespread thunderstorms as weak impulses traverse through the trough overhead. In general, these storms should be of the pulse variety and move E/NE on 15 kts of 0-6km mean wind. However, the impressive thermodynamics in place (PWs over 1.75 inches overlapping MUCAPE of 1000-2000 J/kg) will support rainfall rates of 1-2"/hr, through which any short-term training or repeating rounds could lead to instances of flash flooding. ...Eastern Massachusetts & Rhode Island... A wave of low pressure will be tracking south of Rhode Island during this period keeping some showers and thunderstorms in place across southern New England. Although new accumulations are expected to be modest hourly rates of 1+ inches/hr will be possible. A Marginal Risk area was maintained for this period. Weiss/Campbell Day 3 Valid 12Z Wed Jul 08 2026 - 12Z Thu Jul 09 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY/UPPER GREAT LAKES... ...Northern/Central Plains to the Upper Great Lakes... Scattered to widespread convection will break out across the Northern/Central Plains to the Midwest along and ahead of an eastward tracking frontal boundary. The exact location of the highest QPF remains uncertain however the latest guidance agrees on areal average of 1-2 inches with isolated maximums of 3+ inches will occur from eastern Minnesota to Upper Michigan/northern Wisconsin. Recent rainfall will keep some locations sensitive to addition heavy rainfall. A Slight Risk was maintained for these areas. A broad Marginal spans from eastern Nebraska/northern Kansas to the Great Lakes. Campbell Day 4 and Day 5 Valid 12Z Thu Jul 09 2026 - 12Z Sat Jul 11 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL PLAINS TO MIDWEST... Stronger flow will initially remain along the northern tier of the CONUS early to mid-week with mean upper-ridging across the western to central U.S. Embedded shortwaves rounding the upper-ridge will eventually lead to deepening troughing across the the Midwest and adjacent areas on Thursday. The southward shift of stronger flow aloft into the central Plains east through the Middle Mississippi/Ohio/Tennessee Valleys and Lower Great Lakes will bring more scattered thunderstorm chances across the region. Seasonably high instability and moisture pooling along a southward progressing, wavy cold front will support locally heavy rainfall bringing the threat for at least isolated instances of flash flooding, and broad Marginal Risks of Excessive Rainfall have been outlined for Thursday and Friday. One or more Slight Risks may eventually be necessary with more confidence in the frontal position as storm motions may tend to run generally parallel to the boundary helping to lead to prolonged/repeated rounds of rainfall. Mesoscale convective systems will also be a concern as the upper- flow shifts northwesterly, with at least one signal for organized convection notable in the guidance moving off the central High Plains on Thursday. Putnam 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 $$