FOUS30 KWBC 260840 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 440 AM EDT Fri Jun 26 2026 Day 1 Valid 12Z Fri Jun 26 2026 - 12Z Sat Jun 27 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEAST OKLAHOMA TO CENTRAL WEST VIRGINIA... ...Southern Plains to the Mid-Atlantic... The risk of excessive rainfall will shift from portions of the Plains/Mid-Mississippi Valley early in the period into portions of the Ohio Valley and the middle portions of the Appalachians with a west-facing aspect by tonight as a shortwave makes its way eastwards. An airmass with precipitable water values commonly in the range of 1.75 to 2 inches (~2 standardized anomalies) are already in place along the path of the shortwave. Longitudinal differences remain in placement of the axis of heaviest rainfall...but arrival of more CAM/hi res guidance suggested that only a minor north-south expansion was needed. Sufficiently strong southwesterly flow will linger from the Mid-Mississippi Valley to the central Appalachians to keep the convection progressive. Even so...the presence of 70F dew points and maintained instability overnight near a boundary is often sufficient for prolonged overnight activity across this area. ...Montana into North Dakota... Deep low pressure center shifts from the British Columbia coast to Washington through the period with associated shortwave troughing lifting through Montana. Strong steering flow will keep activity progressive, but the environment for organized convection with potential for training. Moisture looks sufficient with precipitable water anomalies of 1.5 sigma. Corridors of 1-2" rainfall, locally 3" are likely. ...Central High Plains... Increased troughing over the Great Basin promotes return flow up the High Plains with evening convective activity off the Sangre de Cristos and Front Range that spills onto the central High Plains through the night. The risk for repeating cells in a moist environment with precipitable water anomalies some 1.5 sigma above climatological average which still warrants a Marginal Risk for the central High Plains. ...Northern New England... Shortwave low moving through Quebec will allow a trough axis to swing through New England today into tonight. Sufficient instability and mid- level forcing from the disturbance and diurnal heating should lead to enhanced thunderstorms capable of producing 1-3" of rainfall in Maine as well as northern NH/VT. Locally repeating activity could allow localized flash flooding despite moisture being rather limited. Bann Day 2 Valid 12Z Sat Jun 27 2026 - 12Z Sun Jun 28 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHERN PLAINS AND A PORTION OF THE OHIO AND TENNESSEE VALLEYS... ...Ohio Valley... The Slight Risk was shifted a bit farther south than the previous outlook to match the better the placement of moisture pooling and upper level support. The previous expansion still looked good based on the latest suite of deterministic and ensemble suite of QPF combined with the wet antecedent conditions there. ...Mid-Atlantic... Ongoing activity Saturday morning looks to settle over eastern VA/the Delmarva by Saturday afternoon with a risk for localized flash flooding. ...Northern Plains... Energy shedding along with shortwave energy embedded withing the broader flow around a deep upper trough will locally enhance rainfall amounts that may lead to isolated flash flooding over the Northern Plains Saturday afternoon and evening....especially in any supercell cores and multi-cell mergers that transpire once the LLJ kicks in after 00Z. Given an increase of higher amounts clipping a portion of the international border region...opted for a targeted Slight risk area in parts of eastern Montana and North Dakota. Bann Day 3 Valid 12Z Sun Jun 28 2026 - 12Z Mon Jun 29 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 4 and Day 5 Valid 12Z Mon Jun 29 2026 - 12Z Wed Jul 01 2026 Day 4 ...The probability of rainfall exceeding flash flood guidance values is less than 5 percent... Oravec Day 5 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE SOUTHERN HIGH PLAINS, UPPER MISSISSIPPI VALLEY/UPPER LAKES REGION AND ACROSS NORTHERN NY STATE INTO NORTHERN NEW ENGLAND... ...Northern New York State into Northern New England... Westerly low level flow expected to strengthen into the frontal boundary forecast to stretch northwest to southeast from eastern Ontario into northern NY State and northern New England late Tue afternoon into Tuesday night. There is potential for organized convection in the 0000 to 1200 UTC July 1 period along and north of this boundary. The GFS and EC both show PW values becoming very anomalous along and just north of this front, with values 2.5-3+ standard deviation above the mean. While there is still a lot of spread with qpf details at this time range, there is a model signal for organized convection moving northwest to southeast resulting in heavy rains and isolated runoff issues. ...Southern High Plains... PW values expected to rise to 1 to 1.5+ standard deviations above the mean in the broad southwest mid to upper level flow across the Southern High Plains on the west side of the Lower MS closed upper high. Embedded shortwaves in this southwest mid to upper level flow will support increasingly scattered convection in this high PW axis, with locally heavy rains and isolated runoff issues. ...Upper MS Valley... Convection expected to become increasingly active late Tue afternoon into Tue night/early hours of Wed along and ahead of the surface front moving slowly across the Upper MS Valley. Favorable right entrance region jet dynamics ahead of this front in an axis of above average PW values will support potential for heavy rains with organized convection along and ahead of this cold front with isolated runoff issues possible. 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 $$