Yeah I didn't think they were *that* rare.
A couple things I was wrong about though. I knew that auroras were more likely seen at low latitudes in North America as opposed to Europe because the north magnetic pole is currently in northern Canada, but I didn't think the fact that Colorado is a few hundred miles farther west than Detroit would make that much of a difference in geomagnetic latitude. It does though. Denver is at 48.2 N when latitude is referred to the north geomagnetic pole. Detroit, on the other hand, is something like 52.4. Only a little over 2 degrees difference in geographic latitude, but over 4 degrees geomagnetic. So yes, aurora sightings will be significantly less common in Colorado as compared with Michigan, especially in southern Colorado.
Here is a nice link that gives you an idea of how often you should be able to see an aurora (weather permitting). Earlier today I found a link at the same site that actually showed maps of North America and Eurasia with a graphical depiction of how far south an aurora should be visible depending on Kp index, a measure of geomagnetic storm strength that ranges from 0 (no activity) to 9 (extreme magnetic storm). I can't seem to find that link now though. But based on the link above, at Denver's geomagnetic latitude, you need to have a Kp 7-8 storm which is quite unusual - somewhere between 100 and 200 days per 11-year solar cycle. Detroit, on the other hand, should see auroras due to storms with Kp indices between 5 and 6, which occur between 600 and 1700 days per cycle.
The other thing I was wrong about was that auroras are rare today due to the Sun's quiescence - maybe a little less common but by no means rare, as your link points out. I also found
this link showing pictures of a nice aurora in February 2014 taken from central Illinois, which is roughly the same geomagnetic latitude as Denver. The display is low on the horizon, so you'd need a good unobstructed view to the north. But given that and decent weather, it should have been visible from northern and even central Colorado.
Of course it depends on wshere you are in Colorado. The map I mentioned earlier shows that in southern Colorado, you would need a pretty extreme magnetic storm to cause an aurora to come far enough south to be visible there. I don't know where in Colorado
@Clark1961 is based, so maybe he is south of that fringe.
