Based on the weather in Ames, Iowa, United States Of America as of May 2, 2016 7:31am local time

Why? Because it's cold. simple as that.
Current Conditions
Mostly Cloudy
Temp: 41.9°F5.5°C
Wind: 1.7 MPH2.7 KPH
Precipitation: None

Next 2 hours: Yes

Next 4 hours: Yes

Next 8 hours: Yes