Cloud Eclipses Cloud

The anvil of one cumulonimbus cloud obscures another in this scene from Lininger Park in Marion, Iowa around 5:20 PM, Tuesday, July 26, 2011. The underside of the anvil cloud in the foreground contains a smattering of mammatus, which often form in this type of environment--a result of very moist and unstable middle or upper level air, overlying a drier layer. The "eclipsing" of the calvus cloud in the background prevented me from seeing all of its swiftly rising tower. This view looks southeast.