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Weather index

The Iowa DOT uses a weather index to score the severity of the winter weather at each of its maintenance facilities. The index creates a higher score for locations that report longer events, more frequent events, colder temperatures and more snowfall. The duration and frequency of the different events are normalized by the Iowa expected extreme for each event, then scaled by an “importance” factor. High indices correlate to more severe winters.

The index is computed using the following information.
  • The number of:
    • Snow events
    • Freezing Rain events
  • Snowfall in inches
  • The number of hours of:
    • Snow
    • Mixed Precipitation
    • Freezing Rain
    • Blowing Snow
    • Sleet
  • The lowest pavement temperature observed during these precipitation events

Historical Statewide Average is 15.4

Weather Index Map 2009

weather index map

Weather Index Map 2008

weather index map

Weather Index Map 2007

weather index map