Nikon DSLR cameras have a feature called Active D-Lighting that brings up the exposure of dark shadow areas like that one in the middle of your photograph.
You could also think of it as Adaptive
Dynamic Range.
Canon DSLRs have the same kind of feature, but use a different name for it.
Did you make a Raw file of the scene, and did you have the camera set to it's Monochrome option?
The Raw file would be in color.
The made in-the-camera monochrome feature at best makes mediocre B&W photographs.
You can make a much nicer B&W image by post processing the color Raw file. You adjust the monochrome response of each color.
5 Steps To Convert RAW Files To B&W
For lightening (dodge) and darkening (burn) just parts of a photo, color or B&W:
Dodge or burn image areas in Photoshop
I did a quick and dirty edit.
Using Adobe Camera Raw's Adjustment Brush I added .5 EV of exposure to the dark shadow in the middle of the shot and to a variety of other dark areas in the scene. Those were all 'local' edits in that I only applied the edit to parts of the frame, not the entire frame, which would be a global edit.
I subtracted .5 EV from the clouds to separate them , light wise, more from the sky. I then added back .5 EV to those parts of the clouds that should be white.
I set the Clarity slider in the Basic panel to +30, a global edit, to boost the mid-tone contrast of the entire photograph.
In Photoshop I added a narrow black border to the photo.