Wake lows are short-lived mesoscale phenomena. Mesoscale weather ranges from about 5 kilometers to 1,000 kilometers in size.
Wake lows are relatively uncommon. They produce strong winds after a storm moves out. The term “wake low” was defined by Ted Fujita, the same meteorologist who came up with the F-scale ranking of tornadoes. These areas of low-pressure form on the backside of heavy rain, causing winds to surge in at fast speeds.
A mesoscale convective system, or MCS, is a collection of thunderstorms that becomes organized on a scale larger than individual thunderstorms and typically lasts for several hours. MCSs may be accompanied by severe weather hazards: heavy rain, flooding, strong winds, tornadoes and hail.
As a MCS moves out of a region, dry air sinks along the back side of the storm. The sinking air often leads to clearing skies. This descending air warms up rapidly through compression, generating a localized area of low pressure in the storm’s wake. The pressure difference between the rain-cooled air of the MCS and the warm air descending in the storm’s wake, creates a strong pressure gradient that generates strong winds.
Winds speeds can rapidly reach 40 mph to greater than 60 mph. The winds often blow in the direction opposite of the direction the MCS originally traveled, since the wind is rushing toward the storm’s wake.
Wake lows are notoriously difficult to forecast because they rely on the complex decay dynamics of a storm, are of small scale and are not common. The modernization of the National Weather Service improved tracking capability of mesoscale phenomena with Doppler radar, surface observations, satellite observations and finer resolution models. The development of mesoscale weather station networks has improved the ability to locate wake lows.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on Wisconsin Public Radio at noon the last Monday of each month. Send them your questions at stevea@ ssec.wisc.edu or jemarti1@wisc. edu.
