FOUS30 KWBC 072012 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 412 PM EDT Tue Jul 7 2026 Day 1 Valid 16Z Tue Jul 07 2026 - 12Z Wed Jul 08 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN PLAINS/MID-ATLANTIC/NORTHWEST LOUISIANA... 16Z Excessive Rainfall Outlook Update... Introduced a targeted Slight Risk in northwest Louisiana where rainfall from the overnight hours into this morning has lowered flash flood guidance. Radar imagery has shown continued development close to...if not located over...the same area. Given latest models...the expectation is that the risk will diminish with time this afternoon but the potential for rainfall rates to exceed flash flood guidance is heightened for the time being. The Slight risk area was embedded within a broad Marginal Risk area extending northeastward across parts of the Tennessee Valley into the Mid-Atlantic where the risk of excessive rainfall results from slow motion of cells that produce downpours. Elsewhere...few changes were needed based on a quick look at latest guidance. Bann 0830Z Excessive Rainfall Discussion... ...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. Through the day convection is expected to increase in areal coverage 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... Guidance continues to show heavy rainfall potentially exceeding 3 inches locally from southwest Pennsylvania into central Virginia and northeast North Carolina with merging cells near a backdoor front. This part of the region could see isolated to scattered areas of flash flooding, thus a Slight Risk was maintained. A Marginal Risk area remains in effect for much of the Lower Mississippi Valley, Tennessee Valley and the Mid-Atlantic where lingering high moisture and instability should support heavy rainfall rates and localized flash flooding concerns. ...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. Campbell Day 2 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... 20Z Update... The previously issued outlook still in good shape. Even though there were a couple of minor adjustments...there was no fundamental shift in the forecast reasoning. Previous Excessive Rainfall Discussion... ...Central Plains to the Upper Great Lakes... Several locations remain sensitive given recent rains and lowered FFGs, particularly for portions of the Upper Mississippi Valley and Upper Great Lakes. A Slight Risk area remains warranted for this part of the country where areal averages of 1-2 inches are expected with localized swaths of 3+ inches. Convection from overnight may be weakening during the morning hours however redevelopment near the frontal boundary midday should occur over Minnesota and Wisconsin. Approaching shortwave energy and an upper level jet will help drive this uptick in activity, with PWs above the climatological 90th percentile and CAPE approaching 2000 J/kg supporting heavy rainfall rates. While a progressive squall line should eventually evolve, there will be an opportunity for some training and backbuilding during the development and initial upscale growth phase of convection. A Marginal Risk spans from the Central Plains to the Great Lakes and surrounding area. ...Tennessee/Ohio Valley to the Mid-Atlantic... A Marginal Risk was maintained for this region. A shortwave moving across Kentucky/Tennessee and a lingering backdoor front over West Virginia/Virginia should both act as a focus for convective development. Not expecting anything too organized or widespread, but enough moisture and instability will be around to support locally heavy rainfall rates. Campbell Day 3 Valid 12Z Thu Jul 09 2026 - 12Z Fri Jul 10 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN/CENTRAL PLAINS, MIDWEST, OHIO/TENNESSEE VALLEYS AND GREAT LAKES REGION... 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 United States. 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 a better chance for scattered thunderstorms across the region. Seasonably high instability and moisture pooling southward of a wavy cold front will support locally heavy rainfall rates with training potential over the region. That will compound impacts from convection the previous forecast period. A large area of 1-2 inch areal average totals with embedded higher amounts positioned over the southern-third of Illinois/Indiana/Ohio through much of Kentucky into West Virginia. This is coincident with the progression of both the front and a strengthening shortwave trough migrating out of the Central Plains into the region as we move into Friday. Machine Learning output is also favoring the Ohio River Basin into the Central Appalachians extended from southwestern Pennsylvania down through West Virginia as terrain influences along with the synoptic evolution will couple into a targeted threat for heavy rainfall and local maxima sufficient for scattered flash flood prospects. Bann Day 4 and Day 5 Valid 12Z Fri Jul 10 2026 - 12Z Sun Jul 12 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE OHIO/MID-MISSISSIPPI VALLEYS AND CENTRAL APPALACHIANS ON FRIDAY AND SATURDAY... ...Ohio and Mid-Mississippi Valley's... 20Z Update: The previous forecast was generally maintained with the overall synoptic pattern still maintaining continuity in the proposed evolution at both the upper levels and at the surface. Ensembles continue to indicate a multi-day bout of heavy rainfall across the Mid-Mississippi to Ohio Valley in conjunction with both mid-level ascent and the proxy of a cold/quasi-stationary front that will aid in scattered to widespread convective activity in-of a very moist environment positioned over the region. The trends in guidance indicate a bit more emphasis further west into MO with even the D4 showing an extension of heavy rain prospects back into the Southern High Plains thanks to a likely convective complex developing around the eastern flank of a strengthening ridge over the Four Corners. Classic summer pattern materializing for areas west of the Mississippi, so the threat for isolated flash flooding will likely have some footing in the extended with D4 the first prospectus day for the threat. The SLGT risk inherited was expanded into the Mid-Mississippi area of eastern MO on D4 and across southern MO on D5 given the trends. The MRGL risk expands westward into the Southern High Plains on D4. Kleebauer ..Previous Discussion.. Stronger flow will initially remain along the northern tier of the CONUS through 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 by Thursday. The southward shift of stronger flow aloft will bring increasingly widespread storm chances from the central Plains east through the Mississippi Valley into the Ohio/Tennessee Valleys and central Appalachians. Seasonably high instability and moisture pooling along a southward progressing, wavy cold front will lead to multiple rounds of heavy rain- producing storms later this week and into the weekend. Mean flow generally parallel to the east-west oriented front will support clustering/training storms increasing the threat for longer- duration rainfall and higher totals. The embedded waves will help to slow the frontal progression at times also helping to increase the chance for repeated rounds/training of storms. For Friday (day 4), the latest guidance shows widespread areal average rainfall of 1-2" with good overlap between the ensemble means and AI guidance favoring the Ohio/Tennessee Valleys into the central Appalachians, where a Slight Risk has been maintained. While the guidance is not quite as bullish on amounts yet on Saturday (day 5), a similar set up will support additional locally heavy rainfall, with the concern being that much of the mean/AI guidance overlaps similar regions to Friday, favoring the middle to upper Ohio/Tennessee Valleys into the central Appalachians. Given the increasingly wet antecedent conditions expected from the prior days with additional storms likely, another Slight Risk has been introduced. Putnam ...Southwest U.S... Monsoonal activity will finally make an appearance by the end of the week with the threat ramping up into some more appreciable in regards to magnitude and coverage across the terrain of southeastern and central AZ, mainly following the Huachucas up through the Mogollon Rim in east-central AZ. PWATs will surge north along prevailing southerly flow on the western side of the broad upper ridge centered over the Four Corners. QPF signatures are textbook in monsoonal convection billowing up across the terrain at lead which is a good indicator of at least the isolated threat of flash flooding to kick off the Monsoon season across the Southwest. A MRGL risk has been added to account for the threat on D5 with perhaps an upgrade plausible on D4, but signals are not as prolific on Friday compared to Saturday on both the global deterministic and their ensembles. Kleebauer 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 $$