EVANSVILLE – A strange and tough-to-detect weather phenomenon could pop up in the Evansville area this weekend.
According to an advisory from the National Weather Service Friday afternoon, Tri-State residents could see “cold air funnel clouds” − tornado-looking twirls that form in the sky when the ground temperature is significantly warmer than conditions in the atmosphere.
“Cold air funnel clouds will rarely reach the ground, and if they do they typically will cause very minor damage,” the advisory states. “If a report is received of a cold air funnel reaching the ground and causing (damage), a tornado warning will be issued as usual.”
An NWS report compared the funnels’ potential to an EF-0 tornado: the weakest possible twister. Usually, though, they’re “harmless.”
A cold air funnel, a weak tornado that can form when ground temperatures are significantly warmer than conditions in the atmosphere, is seen in Kentucky in 2003.
They “form beneath showers or weak thunderstorms when the air aloft is especially cold,” the NWS states. “The funnels are most common in the fall and spring when the sun is able to heat up the lower levels of the atmosphere, causing convection to bubble up and form showers, but temperatures around 15,000 to 20,000 feet above the ground are quite cold.”
The possibility for their arrival will linger most of the weekend, as multiple rounds of rain and storms usher in significantly cooler weather. Evansville has between a 50% and 80% chance of rain all weekend, but is at a lower risk for anything greater than isolated storms.
The greatest chances for severe weather remain to the south, west and east of the city, although the chance for strong storms here remain. Some areas could see damaging winds and large hail.
After a week of highs in the 70s and 80s, temperatures will stumble into mid- to lower-60s this weekend. That contrast will fuel conditions for the cold-air funnels.
“They are also difficult to detect on radar since they are very weak,” the NWS wrote in its report. “Spotter and public reports are essential when cold air funnels are in the area.”
This article originally appeared on Evansville Courier & Press: What are cold air funnels?