It's not unusual to reach for a mask for images like this one, but good results can usually be achieved quickly without resorting to a mask. In this case, there is plenty of detail in sky and foreground, but it just needs to be brought out a little. I sacrificed contrast in the darker cloud areas. This created enough curve "elbow room" to lighten and increase contrast in the grass. I removed the greenish cast from the clouds by adjusting the center of the a curve, and I made the a and b curves steeper to add color to the grass, and finished up with Photoshop's Unsharp Mask, radius .5 at 125 percent.

Using a mask would avoid having to compromise the sky, but this would take significantly more work, and would also run the risk of an unnatural appearance.

These were the Lab curves used in Curvemeister
The same result may be achieved in Photoshop by converting to Lab mode before using curves.

This is the RGB curve I used for the RGB version of the correction.
In this case, RGB's ability to increase contrast and saturation made the job easier.

Image provided by Tim Denning as part of a question to rec.photo.digital. The original album is on Flickr.