Social media lit up during the late afternoon hours of October 7th, as a short-lived funnel cloud appeared over the southwest side of Metro Tucson. Below is the gallery of images provided by News 4 Tucson viewers on Facebook.
This phenomenon is meteorologically classified as a “cold air funnel”, which is more bark than bite. So what caused it? Here are the three conditions synonymous with cold air funnel development.
1) A large area of low pressure center overhead. Above is the weather map the evening of the 7th, showing a low pressure center around 18,000 feet (500mb) directly above southeastern Arizona. This feature provides the spin in the atmosphere. We usually see these features in Arizona during the Spring, Fall and Winter months.
2) Cold air aloft. The air temperature at 18,000 feet the evening of October 7th was a frosty 7° Fahrenheit (-14° Celsius). Temperatures this cold at the mid-levels make for an unstable atmosphere, leading to third ingredient needed for cold air funnels.
3) Rising air from developing showers/storms. Once the updraft reaches that 18,000 foot level, it gets caught up in the spin of the low pressure center. Thus, a cold air funnel can form.
These funnels are very weak in nature, typically don’t touch the ground and are rarely given a Tornado Warning from the National Weather Service. Cold air funnels are also extremely difficult to forecast. Because they are such a small feature, Doppler radar can’t detect them. Human observation is the main way to forewarn any potential (and unlikely) danger.