Separate from tomorrow's dangerous severe weather outbreak, parts of upstate Michigan, southern Ontario, and western New York will be impacted by a dangerous line of storms through the night tonight. A mesoscale convective system (an organized complex/line of storms) is forming in northwestern Michigan right now, packing damaging winds, frequent lightning, very heavy rain, and even a tornado or two. This line will continue to grow in intensity through the night as it travels through Michigan and eventually into southern Ontario. If it holds together, it'll pass back into the United States and pose a threat to parts of New York and Pennsylvania.
A moderate risk has been issued for upstate Michigan tonight, with the highest risk for damaging winds in the line of storms falling across the areas shaded in the map below.
Here's a radar image of the storms as of 10:07PM EDT:
If the trail of wind damage is long enough, this line might be classified as a derecho before all is said and done. If you live in Michigan, southern Ontario, or western Pennsylvania or New York, you need to make sure you're keeping an eye on the weather tonight.
Make sure your weather radio has fresh batteries to let you know of severe weather in the area. Download the iMapWeather Radio app for iPhone/iPod Touch if you can afford it. It's $9.99 and often warns me of severe weather even before my real weather radio goes off.
Also keep an eye on the Storm Prediction Center and your location National Weather Service office for updates.