SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1228 PM CDT Tue Jul 27 2021 Valid 281200Z - 291200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS EAST-CENTRAL MINNESOTA INTO CENTRAL AND SOUTHERN WISCONSIN... ...SUMMARY... Thunderstorms associated with severe wind gusts, large hail to very large hail, and a couple tornadoes will be possible Wednesday afternoon into Wednesday night across parts of the Upper Midwest and extending into the southern Great Lakes region. ...Upper Midwest into the southern Great Lakes... A cluster or two of showers/thunderstorms may be ongoing Wednesday morning from northern MN southward into perhaps the IA/WI border vicinity within a warm advection regime. This activity will likely dissipate by the late morning. A subtle mid-level disturbance, cresting the mid-level ridge centered over the central Great Plains, will move eastward into western MN by late afternoon. A warm frontal zone will become draped from the southwest Great Lakes northwestward through WI into northern MN. Strong heating and a very moist boundary layer will lead to a very unstable airmass developing by mid afternoon over the Upper Midwest (2500-4000 J/kg MLCAPE, locally higher). Suite of convection-allowing models show an initial cluster of supercells will probably develop during the late afternoon into the early evening. Large to very large hail, severe gusts, and a couple of tornadoes are possible. Enlarged hodographs near the warm front will favor strong mesocyclones but it is unclear how much of a tornado risk will ultimately develop due to storm-scale interactions. Nonetheless, an initial cluster of storms will likely grow upscale into a forward-propagating severe MCS over the western Great Lakes during the evening with localized intense gusts (75+ mph) possible with HP supercell to QLCS transitions or with the more pronounced bowing segments. It seems plausible this MCS will move across southern Lake Michigan into the southern Great Lakes during the overnight. The coverage/intensity of gusts will probably lessen with time as the squall line encounters weaker buoyancy during the pre-dawn hours. ...Central Appalachians/Mid-Atlantic... An upper-level trough is forecast to move southeastward across the Northeast on Wednesday. A moist airmass will likely be in place across parts of the central Appalachians, where moderate instability is forecast to develop by afternoon. Although large-scale forcing will be weak, isolated storms are possible. In addition to the instability, deep-layer shear will be strong enough to contribute to a marginal severe threat. A few marginally severe gusts will be possible in the mid to late afternoon as low-level lapse rates steepen. ..Smith.. 07/27/2021
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