Valid 2026-09-13 12:00 UTC – 2026-09-14 12:00 UTC

THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SUNDAY AFTERNOON AND EVENING IN A CORRIDOR FROM WESTERN NEW ENGLAND THROUGH THE UPPER OHIO VALLEY

Scattered strong storms accompanied by small to marginally severe hail and potential for locally damaging wind gusts may impact parts of the Northeast through upper Ohio Valley Sunday afternoon and evening.

Discussion

Latest model output suggests that the initially notable mid-level low inland of the Pacific Northwest coast by 12Z Sunday may be slower to devolve into an open short wave trough. However, it still is forecast to remain progressive, slowly accelerating northeastward across the northern U.S. Rockies, in advance of a short wave impulse digging toward the northwestern Canadian Prairies. Within the downstream westerlies, models indicate that short wave ridging will build across much of the northern U.S. Great Plains through Upper Midwest, and adjacent portions of the southeastern Canadian Prairies through northwestern Ontario, while downstream troughing digs across Quebec and the lower Great Lakes region into Northeast.

It appears that the primary surface cyclone associated with eastern troughing may migrate from northern Quebec into the Labrador Sea by late Sunday night. However, another surface low may begin to form/consolidate near/northeast of coastal northern New England, with a trailing cold advancing southeast of the lower Great Lakes region into the northern Atlantic Seaboard through Allegheny Plateau by the end of the period. Westward through the Ohio and middle Mississippi Valleys into the central Great Plains, it appears that this front may stall south of the stronger westerlies, with a cool surface high maintaining influence across much of the northern into central Great Plains until it centers shifts east of the upper Mississippi Valley late Sunday night.

Parts of western New England into the Ohio Valley

In the wake of a sheared mid-level perturbation shifting across and east of the northern and middle Atlantic Seaboard during the day, low-level convergence and destabilization ahead of the main cold front advancing to the southeast of the lower Great Lakes region remains unclear. However, both HREF and REFS calibrated thunderstorm guidance suggest at least widely scattered thunderstorm development is probable by or shortly after peak heating Sunday, from the lee of the lower Great Lakes through the upper Ohio Valley. It is possible that this may coincide with sufficient strengthening of westerly flow in the 700-500 mb layer to support modestly organizing thunderstorm activity with potential to produce marginally severe hail and localized damaging wind gusts, before weakening Sunday evening.

North central Great Plains/Middle Missouri Valley vicinity

Latest model output continues to exhibit substantive spread concerning convective potential across the region through this period. It now appears probable that at least a shallow relatively cool/stable boundary layer will remain entrenched as far south and west as Kansas into the northern high plains, beneath warming elevated mixed-layer air advecting north-northeast of the higher terrain. Forcing for ascent downstream of the approaching mid-level low/trough may support increasing thunderstorm development across the Dakotas Sunday night. However, based on forecast soundings, this may be rooted within/above the elevated mixed-layer, with weak CAPE limiting potential for severe hail.

Kerr · 09/12/2026