I'm not up to date on the current models. I got my Sony XR500 back in '09. It does a nice job with some quirks. The biggest quirk being that loud noises can trip the hard drive's shock sensor, which causes the camera to shutdown to protect the drive from being corrupted. Mounted in a dome with 80+ mph of wind is enough to trip it so its an issue on the interstate or in a hell of a wind gust. I believe you can disable this, but then you run the risk of corrupting the drive. This might be a non issue in today's models though.
Here's a few things I'd look for when shopping:
Infinity focus lock. I think most of us have been burned by getting crappy tornado footage by leaving the camcorder in autofocus mode. Can you lock the focus setting at infinity? How easy is it to set? Does it stay locked? Some cameras drop the setting fairly easily, so you'll think you set it and then your camera is hunting for focus during your Campo shot, making it extremely distracting for your viewers. Some cameras will hold the setting even if you turn the camera off. Some have a nice manual focus knob or ring on the lens that you can just crank to set it. You'll almost always want to have infinity locked when shooting storms, or you're too close to your subject. If you have to fumble through menus constantly to set it, its going to be a real pain after awhile.
Framerate. Yeah, get a 1080p camera, but get one that can do 1080-24p. There are fancy cameras that can do 1080-60p. That's almost overkill at this point as a lot of systems can't even do 60p (including all Blu-rays). So you'd be watching the footage on the TV played through the camcorder (if the set does 60p) or on a computer. You'll get better low light performance at 24p though as the shutter can stay open longer. Film is shot at this frame rate so you can still get nice smooth video at this speed. You can burn to Blu-ray at 1080-24p too. My Sony does 1080-60i. The interlaced video should be as good as 30p, but its really not. You lose quality converting to progressive scans, and the interlacing is awkward when editing on and rendering for computers or taking screen shots.
Bit rate. Beyond the resolution (1080) and frame rate (24p,60i,60p), your video quality is going to be determined by the bitrate of the highest quality recording mode. I believe my Sony does 15 or 16 Mbps. Many camcorders today are shooting 20, 25 or higher I believe. You can compare the models against each other using this.
Rolling shutter. I believe all camcorders that record to hard drives or flash memory have a CMOS sensor with a rolling shutter. This causes tearing in your video if the scene changes between frames. This isn't an issue if you're shooting clouds, but you'll definitely see it when shooting lightning. Chasers used to go for camcorders with CCD sensors to avoid this issue. Since this is no longer an option (on a tapeless consumer grade camcorder), you'll just have to compare the models to see which handles the tearing the best. That might be difficult to do without being able to take it for a test drive out of the store so online reviews are probably your best bet there.
Image stabilization. Some camcorders have nasty stabilization that causes the video to degrade into wavy distortions, like your screen has ripples in it. This was an issue with some camcorders when I was in the market a couple years ago, maybe its a non issue today? Anyway, keep an eye out for it. Affected camcorders will shoot great video when they're in your hand in the store. The second you put it on the dash in the car, however, is when you'll notice the motion and bumps in the road distort the video to oblivion.
