COLD AIR FUNNELS
Cold air funnels were reported late Tuesday afternoon in Rockford and near DeKalb. Here is an archived Ask Tom Why from 2001 explaining the meteorology behind the formation of a cold air funnel.
May 25, 2001
Dear Tom,
What are cold air funnels? Jeff Peterson, Huntley, IL
Dear Jeff,
A cold air funnel is a funnel cloud that does not develop in a typical severe weather environment. These funnels tend to form when there is large slow moving low pressure system in the upper atmosphere, similar to the one currently anchored over the Midwest. These cyclonic (counterclockwise) systems generate a lot of vorticity (spin) that enables the funnels to form. Cold air funnels get their name from the pocket of cold air aloft associated with these systems. The cold air produces a very unstable air mass, enabling towering cumulus clouds to rapidly grow into the showers and thunderstorms that produce these funnels. These funnels are weak and short-lived and usually do not touch down. Those that do reach the ground become weak tornadoes (winds often 50 m.p.h. or less) that generally produce only minor damage.
