FOUS30 KWBC 270100 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 900 PM EDT Fri Jun 26 2026 Day 1 Valid 01Z Sat Jun 27 2026 - 12Z Sat Jun 27 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN EFFECT FROM NORTHEAST OKLAHOMA THROUGH SOUTH-CENTRAL MISSOURI... 01Z Update... Forecast confidence was not bolstered by the run-to-run variation in recent runs of the HRRR. But after downplaying the threat for several runs, the latest run (23Z) is once again advertising heavy amounts across southwestern Missouri, which remains likely given the favorable environment and the ongoing development of slow- moving cells over the region. With heavy rainfall and flash expected to become a growing concern through the evening into the overnight, the previous Moderate Risk was mostly maintained from northeastern Oklahoma and far southeastern Kansas through southern Missouri. Refer to WPC MPD #535 for additional information regarding the near-term heavy rainfall and flash flooding threat. The Moderate Risks area was extended a little farther west into north-central Oklahoma -- reflecting the ongoing convection in that area and the HRRR/RRFS signal for training/back- building storms, resulting in heavy amounts and possible flash flooding. Farther east, a Slight Risk was maintained through the lower Ohio Valley, where a separate cluster of storms producing heavy amounts and areas of flash flooding will continue to progress east through the evening. In the wake of these storms, there is the potential for the previously noted storms over the Plains and Ozark Region to track east into this region, further raising the threat for flash flooding. Elsewhere, storms have been mostly isolated across the Northeast, and with the strongest cells expected to move offshore within the next couple of hours, the Marginal Risk was removed. Pereira Previous Discussion... ...Southern Plains to the Mid-Atlantic... 16Z Update...Upgraded to Moderate for northeast Oklahoma, far southeast Kansas, much of southern Missouri, and extreme northern Arkansas. Initial impulse over southeast MO this morning will continue shifting east to the Mid-Atlantic through tonight. Earlier activity south of a lingering stationary front has worked over southern IN for the time being, so an upgrade from Slight is not necessary there through central WV. The next impulse is over the KS/CO border and cross KS through this evening before crossing southern MO overnight. This is the concern that warranted the upgrade to Moderate. Saturated soils, PW increasing to around 2" on a robust LLJ tonight, and increasing instability into the evening. 12Z CAMs are united in a risk for 3-5" rainfall in a few hours from organized activity through the Moderate area. Expanded the Marginal east again through the central Mid-Atlantic where the presence of 70F dew points and maintained instability overnight near a boundary is often sufficient for prolonged overnight activity and at least localized flash flooding. ...Montana into North Dakota... Deep low pressure center shifts from the British Columbia coast to Washington through tonight with associated shortwave troughing lifting through Montana. Strong steering flow will keep activity progressive, but the environment for organized convection with potential for training exists. Moisture looks sufficient with precipitable water anomalies of 1.5 sigma above normal. Corridors of 1-2" rainfall, locally 3" are likely over central MT through central ND where the Marginal remains in place (expanded west just a bit in MT). ...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, now connecting to the farther east risk over south-central KS/western OK. Jackson/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... ...Mid-Mississippi Valley through Southern Appalachians... Expansion of Slight Risk east to west and north given ongoing heavy rain along the Mid-Miss/Ohio Valley frontal zone Saturday morning that then persists into or through the afternoon. Low level westerly flow remains parallel to this boundary, raising concerns for repeating/training activity. The 18Z HRRR seems to have a better handle on activity than the 12Z with final shape of the Marginal and Slight areas adjusted for its 24hr QPF ending 12Z Sunday. Decent consensus for areas of 3-5" rainfall near the KY/TN border with some repeating activity east through the southern/south-central Appalachians. Depending on progress of activity, a localized Moderate may be warranted. ...Mid-Atlantic... Frontal zone now looks to linger over the central Mid-Atlantic through Saturday night rather than shifting shifting south to the VA/NC border Saturday evening. This maintains warm sector enhanced moisture and instability over the DC metros and DelMarVa in addition to southeast VA and the Outer Banks of NC. The Marginal Risk was expanded up to the PA/MD line and down through central NC for waves of heavy thunderstorms expected across these areas through Saturday night. This still looks to be a localized flash flood threat, but a focused Slight Risk may be needed eventually. ...Northern Plains... The upper low tracks over the interior Northwest on Saturday with shortwave troughing ejecting across northern WY and eastern MT by Saturday evening. Low level forcing east of the approaching wave triggers repeating thunderstorms over eastern MT through ND Saturday afternoon which continue through the evening. Increasing LLJ that evening should enhance rainfall with the Slight Risk maintained/expanded west a bit from northeast MT through northwest ND. Activity should be fairly progressive, but the route of the upper trough may pivot/allow repeating activity. Jackson Day 3 Valid 12Z Sun Jun 28 2026 - 12Z Mon Jun 29 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN NORTHWEST MONTANA AND PORTIONS OF THE UPPER MIDWEST... ...Montana... Upper low center pivots over Montana Sunday with the surface low stalling along the MT/Saskatchewan border (aka northeast MT). This maintains comma head/deformation zone rain shifting into northwest MT where terrain enhances rates. 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. 12Z consensus rainfall is 1-3" on ranges around Glacier NP onto the adjacent high plains in northwest MT. A marginal risk has been raised for this area. ...Upper Midwest... The warm sector of this anomalous low over MT will shift east from its position on Saturday. The sector will contain robust Gulf moisture advection up the length of the Great Plains through the Upper Midwest where a warm front will be lifting. Will hone in on the main heavy rain threat area with time, but for now a marginal risk is raised for much of northern MN and northwest WI which is between the consensus of the better Day 3 sources of guidance, the CMC regional (RDPS), EC-AIFS, and RRFS. For the 12Z cycle, the RDPS was the most central of these solutions and was used to draw the Marginal Risk area. PW anomalies through the Upper Midwest should be 2 to 2.5 sigma above normal, so where low level convergence meets the instability gradient a flash flood threat will be warranted. Jackson Day 4 and Day 5 Day 4 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF WEST TEXAS... A Marginal Risk was added across portions of West Texas -- from the Big Bend northward into the Pecos Valley, including the Davis Mountains. Model signal for at least isolated flash flooding concerns has increased, with guidance showing deepening moisture and mid-level energy lifting out ahead of a highly-amplified trough in the west. While the deterministic models differ on the details, many, including the GFS and ECMWF, show PW anomalies increasing to at least 1.5 std dev above normal, along with a slow-moving, low- amplitude shortwave lifting north out of Mexico. This will likely raise the threat for at least isolated storms capable of producing heavy rates and runoff concerns. Pereira 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... 2030Z Update... Made only minor adjustments based on the 12Z guidance. Pereira ...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