This unusual late summer regional tornado outbreak was not well-anticipated in Convective Outlooks issued by the NOAA/NWS Storm Prediction Center (SPC) through the morning of 24 August 2016. A number of factors contributed to this particularly challenging forecast, including earlier numerical model guidance indications that the primary severe threat would be located west of Indiana, from the central Plains into the middle Mississippi Valley. In the short-term, it appeared that ongoing morning and early afternoon convection and prevalent cloud cover across northern/central Indiana and western Ohio would limit the degree of destabilization in these areas. This provided uncertainty about further storm development and intensification of existing convection within the cloudy region. The potential effects of a mesoscale convective vortex (MCV) moving toward northern Indiana raised additional questions about whether strong-to-severe storms could redevelop in the immediate wake of the initial convection. The presence of a very moist air mass and strong low-level shear, particularly near a corridor of differential heating and a related effective warm front across central Indiana at midday, suggested this boundary may provide a key focus for a severe weather threat across this region, and this potential was reflected in the early afternoon (12:30 pm EDT) Day 1 Convective Outlook update.
A continuous weather watch incorporating primarily observational data trends including hourly derived Mesoscale Analysis fields allowed SPC forecasters to monitor closely the evolving situation. In response to rapidly changing environmental conditions and intensifying surface-based convection, Mesoscale Discussion and Tornado Watch products were issued by SPC in advance of nearly all of the day's tornadoes.
This presentation will examine the 24 August 2016 regional tornado outbreak from the perspective of the SPC, particularly with regard to the rapid environmental changes through the late morning and afternoon hours. This will include a review of observational data and trends as well as numerical guidance, including convection-allowing model (CAM) guidance, and a summary of forecasting challenges and opportunities that are illustrated by this event.