Arctic high pressure was centered near Omaha, Nebraska this morning sending temperatures below zero over much of the central United States. Cedar Falls, Iowa dropped to -19 F while the nearby Waterloo, Iowa airport fell to -21 F. Terrain and station location make a difference in overnight lows.
To say that Cedar Falls and Waterloo reached - 19 and -21 respectively is all a matter of where the temperatures were measured. The Cedar Falls temperature was measured in the shelter pictured above, which is in our yard at 922 feet above sea level. The airport is at 873 feet near the bottom of the drainage in the Cedar River Valley. Cold air draining into the river valley on a clear night will usually produce the coldest temperatures. Areas in higher elevations will typically not be as cold. Sometimes the difference will be more the 2 degrees.
So what was the low in Cedar Falls and Waterloo? Good question. As always, it depends on where the temperatures were measured, the surrounding terrain, and whether the measuring location has more urban than rural characteristics. The airport has a more rural setting while the Cedar Falls location is residential so the airport would be colder on a night like last night. On windy or cloudy nights the difference is less.