By October the weather pattern begins to change. Surges of cold air from Canada begin diving south while tropical moisture lurks off the Atlantic coast. Storm systems that were mild and weak in the summer become more powerful by fall as the gradient between warm and cold intensifies.
Severe weather in October is unusual but not unheard of. I’m not overly excited about the potential though the storm system has prompted several tornado warnings in metro D.C. this afternoon. How much instability develops tomorrow will determine what the thunderstorm threat is (more moisture, more sunshine, and more shear will increase the threat). At this point it seems like the best forcing and best instability will be out of phase so the threat for “big” storms like they’re seeing in Virginia and Maryland is low.
Storms like this are a sign of the season. A brisk, seasonably cool weekend will replace the summer-like warmth from last weekend. Overall it looks windy behind Friday’s storm for the marathon on Saturday. At least runners will have a tail wind part of the way!