FOUS30 KWBC 020829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 AM EDT Sun Aug 2 2026 Day 1 Valid 01Z Sun Aug 02 2026 - 12Z Sun Aug 02 2026 ..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA BIG BEND REGION, COASTAL NORTH CAROLINA AND THE EASTERN GREAT LAKES INTO THE NORTHEAST AND NORTHERN/CENTRAL APPALACHIANS... ...East Coast States... Widespread showers and thunderstorms are expected from the Gulf Coast of Florida through the Mid-Atlantic States, and into the interior Northeast. A highly amplified trough will be tracking though the region. A strong upper level jet will help provide impressive synoptic ascent from the Gulf Coast all the way into New England. Meanwhile Gulf moisture will be drawn northward ahead of the system with PW values climbing into the 2-2.25 inches range. Widespread thunderstorm are expected to break out and capable to produce rain rates of 1-2 inches/hour with the potential for repeating/training of cells. A broad Marginal Risk are spans from the eastern Gulf Coast up the Eastern Seaboard to th Northeast and Ohio Valley. There are three areas with a more focused threat. The first is across the Florida Gulf Coast/Big Bend and just inland where heavy rain will occur over recently saturated soils. An additional 3-5 inches of rain is possible (30-50% chance of at least 5 inches) due to backbuilding of cells across the Gulf repeating onshore with 2-3 inches/hour rates. Within this region, an enhanced slight risk was added for Taylor, Dixie, and Lafayette counties which is where the 2-day rainfall is expected to be heaviest. Another area of locally higher excessive rainfall risk exists along the eastern Great Lakes from around Cleveland, Ohio through Buffalo, New York and into the Northern Adirondacks and southward for the Central Appalachians where there is a Slight Risk for excessive rainfall. While instability may be a bit less here, this is also the region where a pivoting deformation axis and accompanying mid- level TROWAL may exist north of the closed low. This will produce some higher thermodynamics into which storms, which will be slow moving and training, can repeat with 1-2 inches/hour rain rates. And the third area is for coastal North Carolina where there is a signal for 2-5 inches of rainfall too fall over recently saturated soils. A Slight Risk area was raised for this part of the state. ..Southwest... During this time the ridge will be expanding eastward however the convective activity is expected to stay suppressed across Arizona, New Mexico and West Texas. The challenge Sunday is that it appears there will be some drying that occurs from NE to SW as a decaying front drops across Texas, followed by a weak surface trough as well. This suggests that during peak heating, there will actually be somewhat of a deterioration of the environment, further limiting convective coverage. Any storms that do develop will have the potential to yield local hourly rates of 1 inch/hour that lead to isolated instances of flash flooding. Campbell/Weiss Day 2 Valid 12Z Sun Aug 02 2026 - 12Z Mon Aug 03 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE TRI-STATE AREA OF NEW YORK, NEW JERSEY, AND CONNECTICUT, COASTAL CAROLINAS AND BIG BEND OF FLORIDA... ...East Coast... The impressive upper trough/low moving across the Ohio Valley is progged to cutoff once again as it digs into the Southeast by Tuesday morning. Downstream of this anomalous feature, robust PWs of more than +2 sigma will flood the Atlantic Seaboard, combining with a ribbon of elevated instability within the deep layer WAA to produce an environment supportive of heavy rainfall for nearly the entire coast. While specific locations for heavier rainfall and a greater excessive rainfall risk are difficult to discern at this time range, it appears nearly any location that received repeating showers and thunderstorms with 1-2 inches/hour rain rates could experienced impacts. The Marginal Risk area stretching from Florida to Maine was maintained. The narrow Slight risk for the Tri-State area of CT/NJ/NY and northwest Rhode Island was maintained due to extremely vulnerable soils from recent heavy rainfall in this area. A small Slight Risk area was raised for the Big Bend of Florida where additional heavy rain may pivot onshore Monday after 2-days of heavy rain this weekend. A Slight Risk was also raised for coastal areas of South and North Carolina given additional rainfall is expected to fall over very saturated soils. ...Southwest... The ridge will continue to expand farther east while weak vorticity impulses rotate around it. Moisture and instability will gradually lift northward during this time, allowing for an expansion north of an environment supportive of heavy rain. The limiting factor Monday appears to be instability. The Marginal Risk area was maintained for isolated instances of excessive rainfall leading to flash flood related impacts are expected for parts of Arizona, New Mexico and far western Texas. ...Northern Plains... A shortwave will quickly track along the International border bringing height falls to the Dakotas and Minnesota. Southwest flow will direct Gulf moisture and instability northward to help support the development of heavy rainfall. Storm motion is expected to be quite progressive however there may be briefs periods where training/backbuilding occurs. As rainfall rates climb to 1+ inches/hour, any training could create locally excessive rainfall. Campbell/Weiss Day 3 Valid 12Z Mon Aug 03 2026 - 12Z Tue Aug 04 2026 ...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHWEST, PLAINS AND MIDWEST, SOUTH FLORIDA AND THE EAST... ...Upper Ohio Valley/Cumberland Plateau/East... Cool air aloft along with ample moisture and instability could lead to hourly rain amounts up to 2.5 inches, which would be problematic in rugged terrain, sensitive soils, and urban areas. There is some overlap with areas that had rainfall during the Day 1 and 2 period, thus maintaining soil sensitivity for potential flooding issues. ...Southwest/Southern High Plains... A Marginal Risk for monsoonal convection across southern Arizona, New Mexico, southern Colorado and into the Texas Panhandle was maintained for this period. Locally heavy rains and isolated runoff issues will be possible in the above average PW values expected across this area. ...Central Plains into the Mid to Upper Mississippi Valley... A slow moving front pushing through the Central Plains and portions of the Mississippi Valley will trigger organized convection for ahead along and ahead of the boundary. PW values expected to be slightly above average...1.5 to 1.75"+ in the vicinity of this front, supporting the potential of hourly rain amounts to 2.5" where convection does organize and isolated runoff issues. A Marginal Risk remains in effect for this part of the country. ...South Florida... Onshore flow will trigger showers and thunderstorms capable of producing 1 to 2+ inches of rainfall that may lead to isolated flash flooding/ponding. A Marginal Risk area was raised for this period. Campbell Day 4 and Day 5 Valid 12Z Wed Aug 05 2026 - 12Z Fri Aug 07 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID TO UPPER MISSISSIPPI VALLEY/MID WEST... ...Mid to Upper Mississippi Valley/Mid West... There is fairly good model qpf agreement on heavy precip potential along and ahead of the cold front sinking southeastward day 4 from the Upper MS Valley/Upper Lakes region. Favorable right entrance region jet dynamics along the southern edge of the westerlies should enhance uvvs in an axis of 1.75"+ PW values in the vicinity of this front. There is a good chance of organized convection along and ahead of the front Wednesday night into the early hours of Thursday, with potential for localized runoff issues. The slight risk area was drawn to encompass the model qpf axis consensus from southern IA/far northern MO, eastward into northern IL/far southern WI, including the Chicago metro area. ...Central Plains into the Lower Missouri Valley... By day 5...additional shortwave energy moving along the southern edge of the westerlies into the Central High Plains may ignite another round of organized convection along the southward moving cold front from KS into MO. Not as good of agreement model qpf wise day 5 compared to day 4 farther to the northeast, but with low level southerly flow expected to strengthen Thursday night into early Friday morning into this front, locally heavy rains are possible. At the moment, the risk level along the front over the Central Plains toward the Lower MO Valley kept at marginal for day 5. ...Southern to Central Appalachians into the Northern Mid- Atlantic... Whatever is left of the upper trof across the eastern U.S. by the beginning of the day 4/5 time period, should continue to weaken. However, an axis of high PW values...1.5-1.75"+, will remain across much of the eastern U.S. in the Wednesday to Friday time frame. This will support additional widespread scattered showers in this high PW axis, with locally heavy rains and runoff issues possible. A marginal risk was continued for both day 4 and 5 across the Southern to Central Appalachians into the northern Mid- Atlantic. After several days of locally heavy rains during the short range period, FFG values will likely be lower through the Southern to Central Appalachians into the Northern Mid Atlantic. This may warrant a greater risk area across these regions with future updates. ...Southwest/Southern High Plains... For the 1200 UTC Wednesday to 1200 UTC Friday time period, a marginal risk was depicted across much of AZ/NM for monsoonal convection. Continued low confidence with qpf details here, but locally heavy rains and isolated runoff issues possible in the above average PW values expected across this area. 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 $$