FOUS30 KWBC 280015 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 815 PM EDT Sat Jun 27 2026 Day 1 Valid 01Z Sun Jun 28 2026 - 12Z Sun Jun 28 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF KENTUCKY & TENNESSEE... ...Mid-Mississippi Valley through Southern Appalachians... The Moderate Risk level elevated by the previous shift was maintained and shifted southeast per the 12z REFS and 18z HREF guidance. This heavy rain area is focused near a prefrontal outflow boundary. Low level westerly flow could lead to non- traditional cell training at times oriented WNW to ESE overnight. While flash flood guidance within much of the realm of the Moderate Risk remains moderate to high, the environment the organized thunderstorms are embedded within (precipitable water values of 2.1-2.2", ML CAPE of 500-2500 J/kg, and effective bulk shear of 25-35 kts) supports very heavy rainfall. Hourly rain amounts to 3" with local totals to 6" are possible in this environment, which would overwhelm urban areas and be problematic elsewhere. ...Mid-Atlantic... The surface analysis remains complex here, with a front near and just south of the Potomac and a prefrontal outflow boundary well to the south across portions of the Carolinas. MU CAPE of 500-2000 J/kg exists here along with effective bulk shear of ~25 kts and precipitable water values of 1.7-2.2". The 12z REFS and 18z HREF continue to percolate convection in this region overnight which could be heavy at times, so left a Marginal Risk out of an abundance of caution. ...Northern High Plains... A broad and unseasonably strong upper level trough lies across the region, with 500 hPa height anomalies of 2.5-3.5 sigmas below the mean for late June across portions of the Great Basin. Low level forcing east of the approaching wave triggers thunderstorms over eastern Montana through North Dakota into the evening, with additional activity under an upper level disturbance across MT. Activity should be fairly progressive, but the route of the upper trough may pivot/allow repeating activity. Roth Day 2 Valid 12Z Sun Jun 28 2026 - 12Z Mon Jun 29 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS EASTERN NORTH CAROLINA INTO FAR SOUTHEAST VIRGINIA... 19z Update: A Slight risk was introduced across eastern NC into far southeast VA. The MCV currently over southern IL will be moving across NC tomorrow. By afternoon a convective focus ahead of this feature should occur across the aforementioned Slight risk area. Guidance indicates a mainly progressive convective mode, however coverage should be enough to result in some cell mergers and brief training enhancing rainfall rates/duration. Both the 12z HREF and REFS indicate a 15-40% chance of FFG exceedance, and rainfall today/tonight could lower FFG a tad more before then. Thus an isolated to scattered flash flood threat appears probable tomorrow afternoon across this region. The Marginal risk was made broader over the Mid-Atalntic as well. Isolated to scattered convection over WV into VA likely won't be as organized as the activity over NC, but could be slower moving and within a favorable environment for heavy rainfall rates. Over eastern TN into northern GA a training convective axis could be ongoing at 12z Sunday, although should be weakening. A Marginal risk was also added over west TX, where dryline convection should pose a localized flash flood risk. Chenard ...Previous Discussion... ...Montana... Upper low center pivots over Montana Sunday with the surface low stalling along the international border . This maintains comma head/deformation zone rain shifting into northwest MT where terrain enhances rates at lower elevations and snow generally at or above 6500 feet. This is more of an areal flood concern given a lack of instability, but localized rates may warrant some rapid flooding concerns where precip bands are most stagnant. 00Z consensus rainfall remained in the 1 to 3 inch range around Glacier National Park onto the adjacent high plains in northwest MT. A marginal risk was maintained for this area. ...Upper Midwest... The warm sector of this anomalous low over MT will shift eastward allowing an airmass with robust Gulf moisture advection up the length of the Great Plains through the Upper Midwest. The development of surface low pressure over South Dakota will aid the moisture transport at the low levels and provide a lifting mechanism. Focusing on this...there was an eastward expansion and a bit of a southward expansion of the previously issued Marginal risk area. ...Coastal Carolinas/Mid-Atlantic... Added a small, targeted Marginal along the eastern seaboard where precipitation lingers from the Day 1 period. Blending disparate QPF in such cases tends to yield low amounts...but the area had the best overlap with highest precipitable water values and an area where ensemble members with differing cores tended to cluster. With such high moisture...localized downpours and heavy to excessive rainfall is a concern from any storm that can develop regardless of the meager focusing mechanism. Bann/Jackson Day 3 Valid 12Z Mon Jun 29 2026 - 12Z Tue Jun 30 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM MONTANA INTO THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY, AS WELL AS ACROSS WEST TEXAS... ...Montana into the Northern Plains and Upper MS Valley... Main change was an expansion of the Marginal risk across this region. Convection should be ongoing Monday morning across portions of the Dakotas within a highly unstable airmass with very strong low level moisture transport. This activity should then push into central/northern MN through the day. Main uncertainty deals with the latitude of the convective axis and mode/movement. Will note that the environment is quite impressive...with extreme CAPE, very strong moisture transport, high PWs and weak Corfidi vectors. Thus the potential is certainly there for an axis of backbuilding convection and a locally significant flash flood risk. However, it's also a possibility that the strong mean flow and somewhat progressive forcing help move storms along and limit the coverage/magnitude of the flash flood risk. So we will just need to continue to monitor trends over the coming days. While mostly stratiform rain by this time, event total rainfall of 2-4" is expected across portions of central and western MT. Even though rainfall rates by this time should be low enough to preclude much of a flash flood risk, this is an impressive amount of rain for late June over this area, and thus some areal/stream flood impacts appear probable. Thus we will include them within the Marginal risk. ...Southwest Texas... Increasing instability should lead to late day convective development along and near the dry line in west Texas. Isolated flash flooding is again possible Chenard Day 4 and Day 5 Valid 12Z Tue Jun 30 2026 - 12Z Thu Jul 02 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS NEW ENGLAND, THE UPPER MIDWEST, SOUTHERN HIGH PLAINS, & CENTRAL GULF COAST... ...Northern New York State into Northern New England... Shortwave energy riding up over the top of the Ohio Valley upper high across southeast Canada into northern New England will help strengthen the low level westerly flow into the frontal boundary forecast to stretch northwest to southeast from eastern Ontario into the region. There is potential for organized convection late on the 30th/early on the 1st near this boundary. There is a strong enough model signal for organized convection moving northwest to southeast resulting in heavy rains and isolated runoff issues, enough for a Marginal Risk, but not cohesive enough amongst the guidance for a stronger risk level. ...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 possible causing problems in burn scars and dry washes/arroyos. ...Upper MS Valley/Upper Lakes... Convection expected to become increasingly active Tuesday into early Thursday 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. There was a southward adjustment in the guidance away from the International Border into portions of the Great Lakes/Northern Plains/Upper Midwest, which caused a similar shift in the existing Marginal Risk area. Additional southerly shifts cannot be ruled out, given the flow pattern expected. ...Central Gulf Coast... Some of the guidance has a signal for heavy rainfall across the area, caused by an easterly wave coming off the tail end of a frontal boundary. Considering the moisture and instability expected, at least urban areas could receive flash flooding so added a Marginal Risk for this possibility. Roth 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 $$