If you've ever been sitting around a bonfire next to a lake and you've noticed the smoke has begun to drift in the opposite direction, you've likely experienced cold air drainage - welcome words on a warm summer night.
Air at relatively high elevation cools in the evening until the point at which it becomes heavier than the air in nearby locations at lower elevation. The heavy cooler air will then sink, or drain, into the lowest nearby point.
This phenomenon occurs in many localized areas across the globe. Regionally, the most dramatic example of cold air drainage occurs at Embarrass, Minn. Famous for its ridiculously low morning temperatures (the town proudly calls itself "The Cold Spot"), Embarrass sits in a depression just north of a ridge that rises over 400 feet. Winter temperatures have reached an unofficial low of 64 below zero, according to area weather observers. Every summer month has recorded a record low that's under 25 degrees above zero. Temperatures have fallen under 30 below during six months of the year.
Locally, one area subject to cold air drainage (to a much lesser degree) is Lake Plantagenet. Elevations to the east of the lake rise as much as 200 feet in just over 2 miles. During summer the cold air will begin to drain down to the lake just before sunset, causing a steady west wind to end and an east wind to begin. Temperatures can drop 10 degrees in less than 10 minutes. This cooling typically lasts less than an hour, after which temperatures become steady or rise slightly.
The next time you kick back around a fire in the evening keep an eye on the smoke - you may be rewarded with a refreshing cool breeze.
Tom Siemers is the Pioneer's circulation manager. Email him at email@example.com