2AM Day 3 Convective Outlook for Wednesday, June 25. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN A CORRIDOR FROM THE NORTHERN HIGH PLAINS INTO THE MIDWEST AND NORTHEAST AND ALSO ACROSS PARTS OF THE SOUTHEAST
SUMMARY
Strong to potentially severe storms are possible Wednesday in a corridor from the northern High Plains into the Midwest and Northeast, and also across parts of the Southeast.
Synopsis
An upper ridge is forecast to persist across parts of the Ohio Valley and Southeast on Wednesday, with some gradual weakening of the ridge expected through the forecast period. Multiple low-amplitude midlevel shortwave troughs will move along the western and northern periphery of the ridge, from the central/northern Plains into the Upper Midwest and Great Lakes. Along the southern periphery of the ridge, a slow-moving mid/upper-level low will is forecast to approach Florida from the Bahamas.
Parts of the central/northern Plains into the Upper Midwest
A remnant MCS may be ongoing somewhere from the north-central Plains into parts of southern MN/northern IA Wednesday morning. This system is currently expected to gradually diminish with time as the nocturnal low-level jet weakens. A localized severe could accompany this remnant MCS through part of the morning.
In the wake of this MCS, diurnal heating of a richly moist environment will support strong destabilization near an outflow-reinforced front. Storm development will be possible along this front/outflow by late afternoon, with MLCAPE potentially in excess of 3000 J/kg supporting vigorous updrafts. Deep-layer flow will be relatively modest, though locally backed winds near the boundary could support initial supercell development, before storm clustering becomes more prominent with time. Damaging winds, isolated hail, and possibly a tornado could accompany the strongest afternoon/evening storms. A corridor of greater severe probabilities may eventually be needed, if confidence increases regarding the evolution of morning convection and placement of remnant surface boundaries.
Farther west, a relatively moist post-frontal regime could again support strong to potentially severe storms across parts of the central/northern High Plains. There is some potential for this region to be in the wake of a departing midlevel shortwave trough during the afternoon and evening, making diurnal storm coverage uncertain. Deep-layer shear will be sufficient for at least an isolated severe threat in the region during the afternoon and evening.
Lower Great Lakes into the Mid Atlantic/Northeast
Scattered storm development will be possible Wednesday afternoon across parts of the lower Great Lakes into the Mid Atlantic and Northeast, along/south of a cold front. While temperatures aloft will be rather warm, diurnal heating will support moderate to locally strong buoyancy. Deep-layer flow/shear is forecast to be relatively weak, but unidirectional west-northwesterly flow could support outflow-dominant clusters capable of at least isolated wind damage.
Parts of the Southeast/Carolinas
A pocket of steep midlevel lapse rates will be in place across parts of the Southeast and Carolinas on Wednesday. The favorable lapse rates combined with strong diurnal heating of a very moist airmass will result in development of strong to extreme instability by afternoon. With some further weakening of the upper ridge, storm coverage may increase compared to previous days.
20-30 kt of northeasterly flow aloft will also develop across parts of the region, to the northwest of the offshore upper low. This modestly enhanced flow could support at least transient storm organization within the very unstable environment. Damaging winds and isolated hail will be possible within this regime. Any loosely organized clustering could result in localized corridors of more concentrated wind damage.