the NOAA Space Environment Center website.
They plot the statistical probability of Aurora Borealis activity based on a number of factors. One NOAA facility helping generate this report is the one located here in Bismarck. The plot looks like this:
If you see North Dakota covered in yellow or red, head out of town and look up! Some times the plot is accurate; other times it's not. It depends on a lot of factors, which is why I'm posting links to many sources below. Granted, many of them draw on exactly the same data set.
It's just my luck, every time I see a good probability on the POES satellite readout, it's cloudy! I hope you have better luck than I. One of these days I'll post some of my Northern Lights photography.
Here are some additional weather / aurora related links you may want to visit:
Solar Terrestrial Dispatch
Solar Data from SOHO and GOES
NOAA's new OVATION aurora product
U of Alaska Geophysical Institute's Aurora Forecast
Having said all that, and posted all these links, let me point out one things: Trying to predict the Northern Lights locally, even with armfuls of data, is slightly helpful at best, wildly unreliable at its worst. The best plan is still to just go someplace dark and wait. You can use this data to determine an active atmosphere, but all the data in the world isn't going to keep you from coming home empty handed.
I've been an avid Aurora Borealis fan since the 1980s, and seen some displays bright enough to read a book by, of all sorts and colors. I've seen spinning overhead vortices, racing sheets of light darting across the sky, and spires of brilliant light dancing in and out of each other on the horizon. I've never found a way to predict them; there's no substitute for simply being in the right place at the right time.
Anyway...try those links up above, spend plenty of time in the dark, and have fun!