Cold air funnel clouds are are generally weak and short lived and rarely touch down.  If they do touch the ground, they are by definition, tornadoes.  This presents quite a dilemma for severe weather warning authorities.  Since they are funnel clouds and tornados, they must be treated as such and warned for. Such warnings and sightings are likely to cause overreaction since these funnels rarely cause significant damage.  Cold air funnel clouds most often form under a "Cold Core" low pressure area where mid and upper level air is very cold relative to the lower levels.  This makes the air mass very unstable and allows any low level moisture to rise rapidly. In addition, the cold low aloft brings with it a "vorticity rich" environment (a lot of upward cyclonic spin).  Add a little afternoon surface heating and towering cumulus clouds can develop quickly. Any of these updrafts that get stretched in the vertical can produce a funnel.  Cold air funnels can occur in a cloud not even tall enough for thunder. Because of this nature of cold air funnels, they often appear without warning.  But meteorologists can predict the systems that cause them, and when advisories are  are necessary, they stress caution more than crawling in a hole.