FOUS30 KWBC 060101 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 901 PM EDT Sun Jul 5 2026 Day 1 Valid 01Z Mon Jul 06 2026 - 12Z Mon Jul 06 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM EASTERN PENNSYLVANIA THROUGH SOUTHEAST NEW YORK... The flash flood threat is increasing this evening across portions of southeast PA into central and northern NJ. Numerous instances of flash flooding are likely overnight, some of which could be locally significant and life-threatening. Latest observational and model trends support the heaviest rainfall totals over southeast PA tonight. This is where we are seeing the best overlap of lower level convergence, instability and PWs over 2". Cells continue to expand in coverage over this area, with some cell backbuilding and training likely to continue. Where cell mergers occur hourly rainfall could be as high as 2-3", with total rainfall as high as 3-5" in spots, mostly falling over a couple hour window. The MDT was risk expanded a bit southwest over PA to capture trends. There is a bit lower confidence over NJ into far southeast NY, with HRRR signals more mixed here. However, recent runs of the experimental WoFS hit this area pretty hard tonight, even showing around a 50% chance of locally exceeding 5". Recent radar trends showing an expansion of convection over central NJ moving northwards is a bit concerning. This very well could build into the convection that is currently over far southeast NY and result in a localized axis of extreme rainfall somewhere over northern NJ or southeast NY. Lower confidence on this evolution compared to what is happening over southeast PA, but nonetheless a significant threat and something to keep an eye on over the next several hours. This area will remain in the MDT risk. Elsewhere isolated to scattered convection over portions of the South will continue to pose an isolated flash flood threat for the next few hours. A forward propagating MCS over central TX should be moving south at a fast enough clip to limit the flash flood threat, but high rainfall rates could be enough to result in localized urban runoff issues, and will thus carry a Marginal risk there as well. Chenard Day 2 Valid 12Z Mon Jul 06 2026 - 12Z Tue Jul 07 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE COASTAL MID-ATLANTIC FROM DELAWARE TO CONNECTICUT... ...Mid-Atlantic and Northeast... Another active day of heavy-rain producing convection is expected Monday as waves of low pressure ripple along a latitudinally wavering stationary front causing multiple rounds of training thunderstorms. At 12Z Monday /start of D2/ this front is progged to be generally aligned west to east from central OH through central NJ, although some variation in this placement is likely due to model uncertainty. 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 PA, the second from NJ into southern New England). Aloft, broad troughing will persist across New England, leaving pinched almost zonal flow towards the Mid-Atlantic, while weak jet energy leaves modest RRQ diffluence in its wake. This synoptic lift will occur within robust thermodynamics characterized by PWs over 2" and MUCAPE rising to 500-1000 J/kg with an intense gradient expected along the aforementioned front. At the same time, moist 850mb inflow will become locally backed and accelerated (still to a modest 15-20 kts) to impinge and isentropically ascend the boundary. Together, these pose a significant risk for heavy rainfall capable of producing flash flooding. Although there remains typical uncertainty into the exact evolution of heavy rain on Monday/Monday night, the threat appears to be increasing for flash flooding. The high-res CAMs are in good agreement that there will be impressive amounts of rainfall (3-6" with embedded much higher totals above 8" as reflected by the REFS and HREF PMM) but the placement varies considerably. This suggests the probabilistic output is critical for evaluating the excessive rainfall outlook, and the recent HREF and REFS 5"/24hr neighborhood probabilities reach above 40% for coastal New England, Long Island, and south through the DelMarVa. In these areas 24-hr probabilities for 8" from both ensemble systems also are notable (20-40%). With the impressive thermodynamics in place, and robust persistent forcing tapping into this, 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. While FFG exceedance probabilities are somewhat modest when compared to the rainfall probabilities (locally 25-40% chance), some of these areas will be experiencing heavy rainfall on D1 which will contribute to the increasing vulnerability on D2. After coordination with the affected WFOs, a MDT risk was raised for portions of eastern PA, NJ, New York City, and southern CT where confidence is highest in training heavy rainfall leading to numerous flash flood instances, some of which could be significant. 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 PA 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 SLGT risk was added across these areas. ...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. However, weak Corfidi vectors of just around 5 kts aligned both to the mean wind and the front will allow for repeating rounds and some short-term training of these intense rainfall rates. Additionally, pulse convection may redevelop along outflows and through collisions, suggesting that some places may experienced multiple rounds of heavy rainfall during primarily the peak- heating hours of Monday. This setup is still supportive of the inherited MRGL risk, and only cosmetic adjustments were made to account for the recent guidance. Weiss Day 3 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... A shortwave cresting the expanding ridge centered over the Four Corners will translate steadily eastward from central MT early D3 to western MN by the end of the forecast period. 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. Together, this will manifest as increasing thunderstorm development most of the day on Tuesday, with activity moving steadily from west to east across MT, while secondary development occurs in the Dakotas along the front itself. Mean storm motions should generally be around 20 kts to the E/NE, but increasing bulk shear to 40-50 kts and aligned Corfidi vectors suggests some backbuilding or training of clusters will develop. 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. This rain will occur atop sensitive soils due to recent heavy rainfall, and 3-hr FFG is as low as 1-1.5"/3hrs. The inherited SLGT risk was modified to account for the recent UFVS first-guess fields, with the MRGL also adjusted for recent model trends and soil vulnerabilities. ...Mid-Atlantic States... Scattered to widespread thunderstorms will develop during the aftn beneath a broad mid-level trough that will remain entrenched over the area. Weak impulses within the weak flow combined with the typical Piedmont trough and other lingering boundaries will be the focus for convection initiation, followed by boundary interactions and mergers leading to additional clusters during peak heating. 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 moving south of Rhode Island at the start of D3 /12Z Tuesday/ will gradually translate east through the morning before exiting by the afternoon. Although there is some spread in the departure speed of this wave, there is enough overlap in the model QPF early Tuesday to add a small MRGL risk for eastern MA, RI, and the Cape/Islands. While additional rainfall D3 may be modest (10-30% chance of 1+"), lingering rates will remain impressive within the high PW airmass, and this will be falling atop soils saturated from what is expected to be heavy rainfall on D2. The small MRGL risk was added to encompass areas with the highest D3 probabilities atop the heaviest QPF footprint from D2. Weiss Day 4 and Day 5 Valid 12Z Wed Jul 08 2026 - 12Z Fri Jul 10 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN GREAT LAKES WEDNESDAY... 20z Update: Only minor changes needed to the inherited risk areas. There is some uncertainty regarding the convective mode and extent of training on Wednesday over the northern Great Lakes, but the multi-model consensus supports a max rainfall axis in line with our ongoing Slight risk. Thus see no reason to deviate from the ongoing forecast. On day 5 we did expand the Marginal risk a bit further west over the Plains as shortwave energy riding over the Western U.S. ridge and an upper level jet streak should support organized convection moving off the High Plains. As mentioned below, there will probably be an embedded Slight risk or two on day 5 as we get closer and confidence increases on the location, but a broad Marginal risk will suffice for now. Chenard ...Previous Discussion... A seasonably moist, unstable airmass will be in place along the northern side of an upper-ridge building over the western to central U.S. early next week. An upper-level wave rounding the top of the ridge will help trigger scattered to widespread thunderstorm development along a frontal boundary through the northern Plains/Upper Midwest Tuesday with ongoing/additional storms spreading into the Upper Great Lakes Wednesday. Storms will likely focus ahead of an eastward moving surface wave along the boundary with clustering/upscale growth potentially leading to a more organized system. Typical uncertainty on the exact location and coverage of convective development remains a concern particularly as the storm evolution Tuesday will likely impact storm development/evolution Wednesday. However, there remains good consensus amongst the deterministic model guidance on areal average rainfall totals in the 1-2" range, locally 3"+, supporting the threat for scattered flash flooding. A Slight Risk of Excessive rainfall is in place from east-central MN into northern WI and the UP/northern LP MI, with the potential for areal adjustment of the risk in subsequent outlooks. The embedded shortwave energy will help to subtly deepen/expand troughing more broadly across the the Midwest and adjacent areas on Thursday. The southward shift of stronger upper-flow aloft into the central Plains east through the Middle Mississippi/Ohio Valleys and Lower Great Lakes will bring more scattered thunderstorm chances across the region. Seasonably high instability and moisture pooling along a southward progressing cold front will support locally heavy rainfall bringing the threat for at least isolated instances of flash flooding, and a broad Marginal Risk of Excessive Rainfall has been outlined. A targeted Slight Risk 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. 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 $$