My best seller was a picture of Comet Hale-Bopp over the University of Virginia Rotunda. It sold very well by word of mouth at the university. Several years ago, a photographer capured a lightning bolt over the same rotunda. It was made into a poster titled "enlightning" ?sp. and it has sold well to UVA students every year. A tornado photo from out west wouldn't sell. If I could get a tornado in Virginia, it probably would sell locally. Thus, if you can capture a weather event with a recognizable landmark, it has a higher chance of selling locally.
Bill makes an excellent point. I've found you have 2 basic kinds of buyers:
(1)-Art Collectors who generally want larger-sized framed prints of high artistic value, and perhaps even of high price. A fellow photographer back in Vermont once told me this and I've found it to be true: the art collectors want to see relatively high prices otherwise they'll assume it isn't WORTH anything!
(2)-Locals or region-familiar tourists/impulse buyers... they'll generally buy smaller prints of a famous local landmark-- something that has SPECIAL MEANING to them.
After selling at art shows in VT, I finally learned which prints to make multiple copies of before a show... popular lakes, picturesque villages, "the leaning-over shed by the river," and "the barn that burned down last year." This has continued to serve me well with consignment items sold in local shops up there.
Cool photographs of lightning or tornadoes might get many compliments, but few buyers. Lightning photography is more likely to appeal to the "high art" crowd, providing it is of high artistic value. Actually, lightning photos might make good "office art" as well. Susan and some of the other "Monsoon Marauders" can probably chime in here. Arizona might have a stronger market for lightning photography since the Monsoon season itself is sort of a local celebrity... those same photos might not sell as well in East Burke, Vermont or El Paso, Texas, at least not amongst the non-art-collecting crowd.
My goal around here is to get a good shot of lightning behind the El Paso skyline. The Wells Fargo Building downtown often colors its windows to light the building up as some shape... Giant Christmas Tree, the letters "UTEP" for the local college sports team, and at this time of year a huge American Flag. I'd bet an ideal shot with that foreground would sell VERY well in El Paso to both major audiences... much like Bill's UVA/Hale Bopp photos.
When selling at shops, make one or two large, framed/matted prints that'll hang on the walls. They'll be pricey, $100-200+... Then make a larger number of smaller, matted, but unframed prints (11x14's) that sell for $30-50 (depends on the local economy and art climate) and put them in a wooden crate or something for flipping through. (Make sure they're in crystal-plastic bags or people will destroy them...)
The big, expensive prints will serve two purposes- they'll act as advertisements, grabbing the attention of shoppers who may then look at your smaller stuff, which compared to the big prints, is much more affordable. The large prints will eventually sell, and at a much higher profit margin. But their value to you may very well be in the "advertising" function.
The small prints will have a small profit margin, but if you know which ones to put out there, you'll sell enough of them and it'll be worth it.
In terms of selling online, I may get about $500-600 in sales per year, with peaks at Christmas time. I have my business card out at my store displays, and also had them all over the place at the art shows. Many customers who bought at art shows have become repeat (some annual) buyers from the web. My main focus with the web site, however, is to act as an online "stock photo catalog," which has had limited success in the Vermont market... mostly local tourist publications which fetch pocket change, but are somehow still very rewarding personally. Getting web traffic is the tough thing. I have an easy to remember URL (vtphoto.com), but yet if you type in "Vermont Photo" "Northeast Kingdom photo," etc. in Google, I don't show up!
The other key is to get your own photo printer that uses ARCHIVAL ink and paper (NO dye-based inks). If you use 3rd party inks such as those sold at MediaStreet.com (which is a higher quality than the stock inks) you'll save a lot of money on ink, and save tons more compared to getting a chemical-based print made at the local lab. I recommend getting a bulk ink tank from MediaStreet rather than mess with cartridge refills.
Good luck!