872 ACUS03 KWNS 291900 SWODY3 SPC AC 291900 Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0200 PM CDT Mon Jun 29 2026 Valid 011200Z - 021200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL PLAINS TO THE UPPER MIDWEST/GREAT LAKES...AND ACROSS THE NORTHEAST... ...SUMMARY... Isolated strong to severe storms will again be possible from the central Plains into the Upper Midwest as well the Northeast on Wednesday. Severe wind gusts and large hail are the main concerns. ...Synopsis... The overall synoptic pattern will not changes much from Day 2/Tuesday into Day 3/Wednesday. The upper ridge over the eastern U.S. may shift slightly east while an upper trough persists over the West. A series of midlevel shortwave impulses will migrate across the northern Plains and Upper Midwest/Great Lakes vicinity. Enhanced mid/upper flow will persist from the Dakotas into the Great Lakes and over the Northeast. ...Upper Midwest/Great Lakes... A quasi-stationary boundary is forecast to extend from northern WI toward southeast SD Wednesday morning. This boundary may slowly lift northward during the afternoon. The evolution of this boundary will largely be influenced by morning convection that may be ongoing near/north of the boundary across parts of MN/WI at the beginning of the period. Given a very moist airmass, strong to extreme instability is forecast near and south of the boundary. Morning convection could weaken as it lifts north of the boundary, or it could intensify through the day as destabilization occurs, spreading east across the Upper Great Lakes. Another round of convection may develop during the late afternoon into the nighttime hours along the boundary as well. While convective evolution is uncertain, the thermodynamic and kinematic parameter space will support a risk for severe wind gusts and large hail. Enhanced low-level shear near the surface boundary could also result in a corridor of tornado potential. Higher severe probabilities will likely be needed in subsequent outlooks as mesoscale details and convective evolution become more clear and forecast confidence increases. ...Northeast... Large-scale ascent will not be as strong across the region on Wednesday, though forecast guidance does show a shortwave impulse or MCV moving across the area as it crosses the international border from Canada. A very moist and strongly unstable airmass will be in place and strengthening mid/upper northwesterly flow will support some organized severe risk. However, storm coverage remains uncertain. Strong downburst winds and isolated large hail will be possible. The wind risk could increase if sufficient storm coverage/interaction results in clustering/bowing segments, but this scenario is uncertain given a lack of stronger low-level jet. Trends will be monitored and higher severe probabilities may be needed in subsequent outlooks. ...Central High Plains... A surface trough will extend southward from western SD/NE into eastern CO/NM on Wednesday. Southerly low-level flow will maintain modest boundary layer moisture beneath steep midlevel lapse rates. Southerly flow through around 500 mb will be somewhat weak, though southwesterly flow increases substantially above that. This could be sufficient for weakly organized convection developing within upslope flow along the surface trough Wednesday afternoon/evening. Given weaker instability and more modest vertical shear compared to previous days, severe potential is more uncertain. However, strong outflow gusts still appear possible given a deeply mixed boundary layer and inverted-v sub-cloud thermodynamic profiles. ...Southeast... Isolated to scattered thunderstorms are likely to develop on the southern periphery of the upper anticyclone Wednesday afternoon. A very moist and strongly unstable airmass will be in place, but vertical shear appears a bit weaker compared to Day 2/Tuesday. Storm coverage is uncertain, but some risk for locally strong gusts may develop, especially if sufficient clustering can occur to promote forward propagation. ..Leitman.. 06/29/2026 $$