Some of what we're driving into... 

I recently found out that this is a "Mammatus" cloud formation. Here is the definition: http://en.wikipedia.org/wiki/Mammatus_clouds I took this photo in North Platte, Nebraska, in August of 2011. We were on a road trip, headed west, on I80. We stopped to eat at the McDonald's, before getting back out onto the road. The weather was scary after that!