Empirical time-dependent equations for ambient air temperature, solar radiation, and wind speed are presented for summer and winter air temperature extremes at two sites for hourly solar radiation-surface meteorological observations (SOLMET): Columbia, Missouri, and Fairbanks, Alaska. The time-dependent equations, in recurrence periods from 1 to 100 years, give engineers a rational basis for selecting a climatic exposure for a desired design period. These time-dependent models may be incorporated into finite element or finite difference heat-flow programs to calculate temperature variations through members of highway structures. Examples demonstrate how a weather exposure may be selected at a geographic location. Mean recurrence of bridge temperature is presented for composite, box girder and T-beam bridges. The Fairbanks, Alaska, models of weather exposure were used previously to study thermal stresses and movements for a 50-year design event in a jointless composite-girder bridge located in the Arctic.