If you look at the front end (in terms of direction of travel) of a thunderstorm of any significance you'll often see the above effect quite clearly. A curtain of air or 'gust front' often descends from the leading edge after plumetting from the top of the cloud and is visible as a semi-circular rim. Large volumes of rain/hail, as well as temp 'mechanics' can add significantly to these gusts, some of which are inherently hazardous.