1AM Day 1 Convective Outlook RESENT 1 for Thursday, June 26. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON ACROSS NORTHERN IOWA AND SOUTHERN WISCONSIN
SUMMARY
A few tornadoes and isolated wind damage will be possible this afternoon from northern Iowa into southwest Wisconsin. Isolated wind damage will be possible across a broad area of the eastern Plains, Ohio Valley, Mid-Atlantic, the Southeast and Montana.
Northern IA/southwest WI area this afternoon
A weak midlevel trough over NE, enhanced by overnight convection, will progress east-northeastward over IA during the afternoon, along with an associated/weak wave along a surface baroclinic zone. Modest enhancement to vertical shear along the baroclinic zone, and MLCAPE near or above 2500 J/kg will support the potential for a band of storms along and ahead of the front this afternoon. The initial/more discrete storms could be supercells with the potential to produce a few tornadoes, in addition to isolated wind damage and marginally severe hail. Convection will likely grow upscale into a line by late afternoon, and the severe threat will begin to diminish by late evening.
Southeast today
Around the southeast periphery of a weakening midlevel high over KY, a midlevel low will drift slowly west-northwestward over FL and weaken gradually through tonight. Widespread convection is still ongoing from late Wednesday evening across AL/GA, with relatively widespread convective overturning and associated outflow. Remnant outflows and differential heating zones will play a role in additional thunderstorm development later this afternoon, though regional reductions in surface temperatures/moisture from yesterday will make the environment less favorable for widespread damaging downbursts compared to Wednesday. Given the mesoscale complexity of the pattern and reductions in lapse rates/buoyancy, will hold off on adding any SLGT risk/15% wind areas in this outlook. However, some part of GA/AL/MS may need to be reconsidered in later updates.
OH Valley into the Mid-Atlantic this afternoon
Scattered thunderstorms are expected again this afternoon in association with daytime heating, residual boundaries from prior convection, and terrain circulations. Though vertical shear will be weak, steepening low-level lapse rates and precipitation loading could support isolated wind damage with downbursts from mid afternoon into the evening.
Western OK to northeast KS this afternoon/evening
Scattered thunderstorm development is expected this afternoon along and ahead of weak front across KS, and farther to the south into the strongly heated airmass and east edge of the midlevel moisture plume now across west TX. Vertical shear will be weak through this corridor, but thermodynamic profiles will favor strong downdrafts and the potential for isolated strong-severe outflow gusts for a few hours this afternoon/evening.
MT this afternoon/evening
A subtle midlevel trough and associated/diffuse front will move across the northern Rockies this afternoon into tonight. Deep mixing and inverted-V profiles will favor some potential for strong-severe outflow gusts with scattered high-based thunderstorms along and ahead of the diffuse front this afternoon into this evening.