Meteorology: Understanding the Atmosphere Ackerman and Knox
The passage of a dying thunderstorm can sometimes be the cause for high winds in summer. Behind a few storms, a small region of very low pressure called a wake low develops. It's called a "wake low" because it forms behind the path of, or in the wake of, the thunderstorm. The pressure gradient near a wake low is very strong-a large change in pressure over a short distance. Therefore, the air blows straight from high to low pressure. Since the storm is passing, this creates the unusual situation of high winds blowing toward, not away from, a thunderstorm that is dying and leaving your vicinity.
On June 30, 1993, a thunderstorm on the northern fringe of the storms causing the 1993 Upper Mississippi floods triggered a wake low that passed through Madison, Wisconsin. A remarkable change in pressure occurred in Madison during a few short hours early in the morning of the 30th: a drop of 16 millibars in less than 2 hours! Sleepy residents awoke to strong and sustained winds of up to 50 mph, even though the thunderstorm had already passed through the city and was diminishing. This is a reminder that strong winds are related to strong pressure gradients, no matter what the situation is. Here is the co-author's impressions of this particular windstorm in poem form: