Funnel clouds were spotted across Oklahoma on Wednesday, March 21st but they weren’t the type of funnel clouds that lead to violent tornadoes. They’re spinning clouds known as “cold air funnels” and rarely reach the surface. When they do reach the ground, they typical bring weak winds from 20-40mph.
These funnel clouds typically form directly underneath a strong upper low pressure area. Upper level low pressure systems are cold core systems that typically spawn showers and thunderstorms in the afternoon and evening. Because of their cold core nature, hail is typically the biggest concern. However, with intense upper lows and strong surface heating the temperature decreases rapidly with height. In meteorology we call this a “lapse rate”. This low pressure system has a very steep decrease of temperature with height or a “steep lapse rate” which means hail will be possible with any thunderstorms. If warm air climbs rapidly into the cold air, cold air funnels might develop. They were widespread across Oklahoma on Wednesday.
Cold air funnels are an unusual occurrence across the south but form very differently from tornadoes that we typically see. A strong spring time tornado usually forms from a supercell thunderstorms (a storm with a central updraft and central downdraft). Tornadoes develop under the updraft of rapidly rising air and form out of an area of deep rotation that extends from the middle all the way up into the thunderstorm called a “mesocyclone”. Unlike a supercell tornado, cold air funnels do not have deep mid-level rotation and lack a mesocyclone. The lack of persistent and deep rotation usually results in funnel clouds that look exactly like their counterparts but not nearly as strong or persistent. In fact, they usually don’t even show up on radar.
Storms that form directly underneath the cold upper level low pressure are also much shorter than supercell storms. We refer to them as “low topped” storms because their tops usually don’t appear over 25 thousand feet. An even more unusual occurrence is known as a “low topped supercell” which is different than a cold air funnel and more like a typical spring thunderstorm cell only much shorter and can actually produce stronger tornadoes. No significant “low topped supercells” formed with this low pressure system but there were numerous funnel clouds.
An unusual way to start the first full day of the 2012 Spring season.
-Garrett