June 02, 2009
The photo above shows the roof of my house in Arlington Heights, Illinois (northwest of Chicago) following a heavy rain on April 26, 2009. Soon after the storms departed, dumping over an inch of rain (approximately 30 mm), a quick warm up occurred. Once the Sun came out, the temperature rose from 43 degrees F (6 C) to 67 degrees F (20 C) within 2 hours. This rapid warm up accelerated the evaporation from the rain-soaked shingles, and since turbulence due to wind was minimal, water droplets quickly condensed above the roofs. We quite enjoyed watching these swirling roof-top patterns. This display continued for about 30 minutes, until the shingles were mostly dry. In essence, each roof had its own microclimate.