BLOG: One-Two Punch of Weekend Severe Weather?

It's a beautiful Summer day today, but trouble may be on the horizon for the weekend. So lets get right to it. While we are enjoying unseasonably cool temperatures, high heat continues to bake the Plains: That dome of heat is going to start migrating east today. While it will not turn HOT here in eastern Ohio and western Pennsylvania, it will turn warmer and more humid tonight into Saturday. Here's Saturday morning's surface map, showing the leading edge of that warmer air: As that warm air runs into the cooler air, it will be forced to rise over it, since warm air is less dense than cool air. That rising air will create spotty shower and thunderstorm activity during the day Saturday. Here's the midday simulated radar off of the NAM model: Notice how "hit-or-miss" the activity will be.The threat for severe weather will ramp up toward evening. By that time, the atmosphere will have gotten quite unstable across our region (especially to the west of Youngstown), as shown on this map displaying CAPE (Convective Available Potential Energy) values: A complex of thunderstorms is likely to form somewhere in that zone of very high instability. Last night's NAM model placed it in Illinois and Indiana at 5pm: Then, the model intensified the complex and took it into Ohio later in the evening: If this model were to have EXACTLY the right idea (unlikely at this point), that would be a severe wind damage threat for southern Ohio particularly. That "bowing" shown on the simulated radar in SW Ohio is unsettling; that just screams "huge area of wind damage".The Storm Prediction Center outlook for Saturday and Saturday night has all of the region in the Elevated Risk (yellow): But, they also see that odds may favor the HIGHEST risk of severe weather being SW of Youngstown. This map shows the percent chance of severe weather within 25 mils of any location: All that said, let's not dismiss the chance for severe weather across the Mahoning and Shenango Valleys. It's still a period where the risk is elevated, even if the overall HIGHEST risk is to our southwest. The main threat from storms here will be damaging winds. Wind speeds aloft will be getting stronger and any hefty storm could pull some of that wind down to the surface. Winds at 5,000 feet will be up around 40-60 mph and tall thunderstorms can pull down winds from above that level easily: Additionally, directional wind shear (the changing of wind direction with height) will be pretty significant: This shear will help aid thunderstorm development and also means that an isolated tornado is something we cannot rule out. Here's a look at the threats Saturday evening: Ok what about Sunday???On Sunday, a strong cold front will be pushing into the Ohio Valley and Great Lakes. Ahead of the front, the atmosphere will be warm and unstable. The big complex of storms that likely rolled through southern and eastern Ohio overnight will keep pushing to the east and the atmosphere will get a chance to "reload", especially if there is a long interval of sunshine.  Here's a look at Sunday afternoon's expected CAPE values: THe Storm Prediction Center has us in the Elevated Risk again: So, we expect scattered strong storms to fire along and ahead of that cold front. Much like Saturday, the highest risk will be from damaging winds....but some hail is also possible.Meteorologist Mike Joyce will be in the Weather Center this weekend. Be sure to follow him on Twitter and Facebook. Have a good, safe weekend everyone.Eric