As cool temperatures prevail across the area, people wonder why readings at the airport and campus differ, and why neither of them agree with the readings on their own thermometer. One reason for the difference is the change in elevation between campus and the airport. Cold air sinks, and will collect in low lying areas, such as the river valley where the airport is located. That’s why forecasters will warn “frost might occur in low-lying areas”. Another factor that can affect night-time lows is the microclimate, or natural setting, around the weather station. Stations in an urban setting, with lots of trees, buildings and parking lots, will generally have warmer low temperatures, than nearby rural areas. These differences are often referred to as “microclimates”.
Mary Knapp, Weather Data Library