A model for forecasting frost accumulation on bridge decks based on RWIS data

Bridge frost presents a potential hazard to the motoring public in cold climates, particularly in early morning under conditions of radiational cooling of bridge decks. A frost forecast model based on simple concepts of moisture flux to the surface has been developed that uses current RWIS-measured temperatures and forecasts of dew-point temperature, air temperature, surface temperature, and wind speed for specific locations. The model uses this information to calculate expected amounts of accumulated frost on bridges. A key parameter being determined is the threshold accumulated frost as calculated by the model that corresponds to the minimum observable frost as seen by a department of transportation maintenance division employee as viewed from inside a vehicle while making surveys of bridges. A logistical regression procedure determines the probability that a maintenance worker will observe frost. The model is being tested and evaluated by comparing model- generated maximum frost depth with daily observations by Iowa Department of Transportation maintenance personnel. Curves of relative operating characteristics (ROC) are being used to evaluate the skill of the modeling procedure.