Approaching Storm Pictures

A storm just rolled through at the airport where I work. Nothing severe here in South Bend but the approaching cell had a beautiful shelf cloud attached. I took these photos with my cell phone so the quality is sub par.

North end of the cloud (and storm):

There has been several reports of trees and power lines down, due to 65-70 mph winds in the southern counties of Michiana. The storm was tornado warned but nothing confirmed yet. Here's the radar image of what your looking at (actually this is an earlier image, radar data for the time of those photos is missing):

Plotted along side the radar is downdraft CAPE. The larger values indicate stronger downdraft potential with convective storm cells. When you have convection in a storm, air is lifted and condenses into precipitation. This precip has a cooling effect and thus you get cold air that sinks ahead of the convection. This cold, sinking air is what shapes the shelf cloud. They form ahead of storms that have strong downdrafts. If you get enough downdraft from a cell it can form a gust front at the outflow boundary, which is basically a storm induced cold front. In the radar image you can see the gust front as it formed some smaller thunderstorms ahead of the larger cell.