f_sky1, created from this image:

http://www.photolib.noaa.gov/htmls/wea03065.htm

Image ID: wea03065, NOAA's National Weather Service (NWS) Collection
Location: Colorado Rocky Mountains
Photographer: Sean Linehan, NOAA NOS/NGS

This is a public domain image, as it is created by an agent of the 
United States Government.

