The above image was taken by the Cheyenne, WY (KCYS) NEXRAD a moment ago. It's in reflectivity mode, which shows all precipitation echoes being sent to the radar (rain, hail, etc.).
This storm is also rotating, as shown by the strong "mesocyclone" on the Storm Relative Velocity (wind motion) image taken at the same time, below:
Note the strong motion toward and away from the radar associated with the storm (just Southeast of Harrisburg). This is what is referred to as a mesocyclone. Remember that green/blue colors are motion toward the radar while red/orange colors are motion away from the radar. The radar is located just off of the lower left corner of the screen.