FOUS30 KWBC 051545 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1145 AM EDT Sun Jul 5 2026 Day 1 Valid 12Z Sun Jul 05 2026 - 12Z Mon Jul 06 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM EASTERN PENNSYLVANIA THROUGH SOUTHEAST NEW YORK... ...Ohio Valley into the Mid-Atlantic & Northeast... Impressive plume of tropical moisture extending from the Gulf Coast through Southern New England will produce an environment favorable for heavy rainfall today. 12Z RAOBs from PIT/IAD/OKX all measured PWs between 1.75 and 1.95 inches, well above the 90th percentile for the date and nearing daily-records. This is suggestive of the tropical airmass, and weak lapse rates within a saturated column with freezing levels nearing 14,000 ft point towards an environment which will support heavy rainfall in all thunderstorms today. Forcing for ascent into this environment will become increasingly robust through the day as well. A front analyzed by WPC draped from Illinois to Long Island will oscillate north/south today as a stationary front, along which waves of low pressure will ripple eastward, aided by shortwaves pushing eastward within the flow. These waves will not only provide enhanced ascent, but also force locally accelerated moist inflow and shear to create clusters of more organized convection with heavier rainfall. This is reflected by both HREF and REFS probabilities that exceed 40% for 2"/hr rainfall rates, this morning/aftn in the OH VLY and then this evening for the Mid-Atlantic states. With Corfidi vectors aligned to the mean 0-6km wind, backbuilding/training of echoes is likely, so corridors of heavy rain exceeding 3" are likely (60-80% chance) with more than 5" possible (30-50%) chance. The greatest risk areas for the heaviest rain are focused in SE MI/NW OH as well as eastern PA/northern NJ/southeast NY where HREF probabilities for 8"/24hrs show low but meaningful (5-10%) probabilities. While soil moisture according to NASA SPoRT is well below normal in the former (0-40cm soil moisture in the 10th percentile), it is much more saturated in PA/NJ. Adding in the urban influences across PA/NJ/NY, the inherited MDT risk still appears needed, and has been expanded northeast into far southeast Upstate NY to account for latest trends. At this time, New York City appears to remain just west of the heaviest rainfall so was excluded from the MDT risk area, but otherwise, it appears likely that numerous impacts from flash flooding will occur today in this area, with locally significant events possible. ...Southern Plains and Gulf Coast through the Tennessee Valley... Broad mid-level trough will remain aligned SW to NE from Texas through Kentucky through today. Within this trough, several weak mid-level impulses are progged to rotate E/NE through the flow, providing locally enhanced ascent within an already unstable atmosphere characterized by widespread MUCAPE around 3000 J/kg. At the surface, a weak cold front will drop southeast, reaching along a line from Kentucky to the Red River Valley of the South by this evening before stalling. The overlap of the weak impulses on this baroclinic gradient will help create ripples of low pressure, and this extra lift will help create scattered thunderstorms today. PW anomalies of +1 (to locally +1.5) sigma will support heavy rainfall rates of 1-3"/hr, which through weak storm motions (0-6km mean winds of just 5-10 kts and variable direction) will create areas of heavy rainfall capable of producing at least isolated instances of flash flooding. Both the HREF and REFS 24-hr neighborhood rainfall probabilities show scattered areas of greater than 30% chance for at least 3" of rain in a large area, but the weak shear to support generally pulse convection should limit more widespread/organized amounts to this level. In general, the inherited MRGL risk was maintained with only cosmetic adjustments. However, an expansion west of the MRGL was created along the Red River Valley near the OK/TX border for some potential multi-cell development exhibiting short-term training tonight. ...Florida Peninsula... After coordination with WFOs MLB/JAX, added a small MRGL risk for the eastern third of the Florida Peninsula for today. Ridge of high pressure centered just west of the state will produce generally weak mean flow, but with subtle upper diffluence. Generally SW winds will help convection track slowly northeast into the aftn/eve, which will likely result in sea-breeze collisions on the Atlantic Coast later today with storms stalling/regenerating in the pulse environment. PWs above 2" will support 1-3"/hr rain rates (30-50% chance for 2"/hr from both the REFS and HREF), which through stalling/slow motions could result in areas of 3-5" of rainfall. Should any storms stall across the more urban areas or atop soils more sensitive from 24-hr rainfall as much as 4", instances of flash flooding could result. Weiss Day 2 Valid 12Z Mon Jul 06 2026 - 12Z Tue Jul 07 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID-ATLANTIC/NORTHEAST... The threat for excessive rainfall and scattered areas of flash flooding will remain for portion of the Mid-Atlantic for this period. Rainfall occurring during the Day 1 and Day 2 periods may lead to increased soil saturation and lowered flash flood guidance for this region, thus making it more sensitive for additional heavy rainfall. Near and just south of this front instability of 2000 J/kg or greater and PWs over 2" are forecast, an environment supporting efficient rainfall and high hourly rates. The inherited Slight Risk area was adjusted to reflect the latest trends and WPC QPF placement. As follows, the southern boundary of the Slight was extended south toward the Virginia and North Carolina border to capture locations were hi-res guidance is suggesting localized 3+ inches, particularly along I-95 and adjacent urban areas. Stronger low level convergence will be capable of producing a broader area of moderate to locally heavy rainfall across New York into southern New England. However a limiting factor will be reduced availability of instability-- rainfall rates will likely not peak as high as those further south. Thus, this area is covered by a broad Marginal Risk from portions of Upstate New York to the Cape, south to the Carolinas and then southwest into Arkansas and northern Louisiana. ...Montana... Isolated instances of heavy rainfall will be possible capable of producing localized flash flooding possible for areas ahead of and along an approaching front. A shortwave trough rounding the base of the building southwestern ridge will trigger convection. A Marginal Risk was maintained as well as expanded to the west/southwest to cover mover of central/western parts of the state. Campbell 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 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 ridge will help trigger scattered to widespread thunderstorm development at the leading edge of the deeper moisture over the northern High Plains. Propagation ahead of a developing surface wave along a quasi-stationary frontal boundary and developing low- level jet will help maintain storms into the overnight hours through the northern Plains with the potential for at least organized clusters of storms if not a mesoscale convective system. Good consensus amongst the deterministic model guidance on areal average totals in the 1-2" range and locally higher amounts of 3-4" supports the threat for scattered flash flooding. A Slight Risk is in effect for portions of the Dakotas and into west/central Minnesota. A Marginal Risk area spans from eastern Montana, most of the Dakotas and Minnesota, far northwest Iowa and northwest Wisconsin. ...Mid-Atlantic to Carolinas... Persistent troughing over the region along adequate instability and PW values around 2 inches will keep convection across the area for this period. Isolated to scattered convection capable of heavy rainfall rates will maintain a Marginal Risk for excessive rainfall in place for this period. Putnam/Campbell 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 UPPER GREAT LAKES WEDNESDAY... 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 $$