Excerpt from web site cited below:

To see aurora you need clear and dark sky. During very large auroral events, the aurora may be seen throughout the US and Europe, but these events are rare. During an extreme event in 1958, aurora was reported to be seen from Mexico City. During average activity levels, auroral displays will be overhead at high northern or southern latitudes. Places like Fairbanks, Alaska, Dawson City, Yukon, Yellowknife, NWT, Gillam, Manitoba, the southern tip of Greenland, Reykjavik, Iceland, Tromso, Norway, and the northern coast of Siberia have a good chance to have the aurora overhead. In North Dakota, Michigan, Quebec, and central Scandinavia, you might be able to see aurora on the northern horizon when activity picks up a little.

The aurora (northern and southern) are created when charged particles from the Sun strike the magnetosphere of the Earth at heights from 60 to about 600 miles and are carried toward the magnetic poles. When the charged particles strike the atoms and molecules in the upper atmosphere, they cause the atoms to emit light in a variety of shades. I live in Ohio and have seen reds, greens, white, and blues. The colors vary depending upon the energy of the charged particles and the atoms or ions they strike (usually nitrogen and oxygen).
Aurora are most intense and seen over the widest areas (furthest south) when the sun is extremely active (at the height of its sunspot cycle, roughly every 11 years).

Edit for Bakerman:

I remember seeing an extremely bright showing of the Aurora from my home in western Pennsylvania. I think it was in the fall of 1968 (I was only in that home from 1968-1969). That was around the peak of solar cycle 20.