Dr. Marshall Shepherd of UGA published a new column in Forbes.com this week about mammatus clouds, the beautiful and sometimes scary clouds that form on the undersides of severe thunderstorms (and occasionally in other places as well).  You can read his blog post here.  The Cloud Appreciation Society also has some great pictures of mammatus clouds at https://cloudappreciationsociety.org/.

Source: Zachary Houri, Commons Wikimedia
Source: Zachary Houri, Commons Wikimedia