Transcript for Powerful storms lash the Northeast, dropping tennis ball-size hail

breaking news, both on that volcano, new pictures coming in right now, and the severe storms moving through. Watches in ten states as we come on the air. Blasting through New York City just a short time ago. Day turning into night and the shadow of the empire state building. Storm clouds moving in and quickly. Hail slamming down, forcing cars to the side of the road, just as many head home from work. Hundreds of flights canceled and delayed at this hour. Thousands without power. ABC's gio Benitez leading us off. Reporter: Tonight, strong storming lashing the northeast. On interstate 87 in New York, torrential rainmaking it impossible to see. Tractor trailers smashing, workers racing to clear trees from the roadway. Hail, some of it tennis ball-sized, destroying windshields. My goodness. Look at the whole truck. Reporter: Those storm clouds romming into New York City. This is a really dangerous situation as we go into the early evening hours. Reporter: Wind gusts downing trees and knocking out power for almost half a million customers across the region. Overnight, powerful straight-line winds pummelling the mid-atlantic. Tornado warnings and wind gunss topping 60 miles an hour at dulles airport. Travelers there forced to hide underground. Lightning sparked this house fire. Our David Kerley on the scene. And you can see, it struck this roof here. It caused quite a fire. 70 fire fighters had to empty out that attic to get this blaze out. Reporter: Further west, hail turned roads into rivers near Denver. And four tornadoes reported in Kansas. Just extraordinary pictures coming in at this hour. We can see the commute home there behind you, gio. He's live on the west side highway tonight. A rough ride for millions. And you're already seeing flights effected here in the northeast? Reporter: That's right, David. Hundreds of flights have been delayed or canceled here in the northeast. That number is only growing, but I got to tell you, the wind here was so strong, come over here, just so you can see this, while we were standing here, look at what the wind did to this massive light post here, David. All right, gio Benitez leading us off tonight. Thank you. Let's get right to ginger zee who has been in the newsroom with us, because you said this would come through and very quickly. Reporter: And the worst timing poblg. Right in the evening commute for millions of people. And let me take you to the map. Philadelphia is getting hit, all the way up to just south of Boston. And this line extends further south. We got a new severe thunderstorm watch that includes Baltimore and D.C. Going to be a raucous night for them. It becomes a stationary front. Stationary is the epitome of the word. It just sits there and moisture pools up against it. So, flash flooding overnight could be an issue. That low south in Florida, causing already six inches of rain, up to four more. Wow. But stationary tonight in the northeast. Going to be pounding through midday tomorrow. Gio and ginger here with us, thank you both for leading us off.

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