Severe thunderstorms will occur from northeastern Iowa across the Lower Great Lakes and Ohio River Valley into the Mid Atlantic today and tonight. The area of greatest risk extends from northern Illinois southeast across Indiana and into Western Ohio.
A surface low pressure system parked over the Central Plains has an associated warm front extending from Iowa into Illinois, Indiana and east into the Mid Atlantic. This surface system will combine with a strong upper level system to create an unstable atmosphere, especially along and north of the warm front. While showers and thunderstorms have impacted this area through the morning, there is a general weakening trend with this morning activity. So the atmosphere will be able to destabilize again this afternoon and even be enhanced by the dynamics with the upper level system.
Severe Weather Threat
NWS Storm Prediction Center has outlined a broad are of Slight risk for severe thunderstorms from northeastern Iowa to across the Lower Great Lakes, Ohio River Valley into the Mid Atlantic.
A focused area of Moderate risk extends from Dubuque, IA to Chicago, IL, South Bend and Muncie, IN to Dayton and Columbus, OH. A broader are of Enhance risk surrounds the Moderate risk from Northeast Iowa to Western West Virginia.
The initial redevelopment later this afternoon will be individual cells and they will have the potential of large hail and isolated tornadoes. But the individual cells will combine to form a line. As the storms become more of a line the main severe weather threat will transition to widespread damaging winds.
The graphics below highlight the individual risk of straight line winds, tornadoes and hail.
There is concern that this line could reach the classification of a Derecho which is a long lived line of storms that produces severe thunderstorm winds of 58 mph and greater for roughly a 250 mile length. Frequently Derecho’s can include areas of winds of 75 to 100+ mph which lead to widespread damage of downed trees, power lines and etc.
NWS SPC has additional information of a Derecho.
With the threat of a long lived line of damaging winds, anyone outside would be at risk of flying debris. In addition, those that are driving are at risk for falling branches, trees and power polls. High profile vehicles such as RV’s and trucks may be blown over.
Even if you are indoors, staying away from windows is wise as flying debris can shatter through a window. In addition, the impacts of a strong straight line winds on a mobile home are similar to a tornado; so a mobile home would not be a wise shelter option.
Early this afternoon is the time to be proactive and move any easily lofted items indoors. In addition plan your activities for later this afternoon and evening to be able to take shelter immediately if storms develop in your area. These storms will have the potential to move very quickly; so you may have limited heads up notice when warnings are issued or when you see the first strobe of lightning and hear thunder.
If you have animals that may be injured by flying debris, moving them indoors or to an area where they can shelter would be wise.
The team at WxIntegrations will continue to provide relevant information and resources to help you better understand and prepare by incorporating weather impacts into your planning and response.