Air and road surface temperature variations during weather change

In this study, thermal mapping along the road and recordings from field sta tions in the Swedish Road Weather Information System (RWIS) are analysed. T he purpose is to explore how long it takes for air and road surface tempera tures to adjust from clear to overcast conditions after a warm front arriva l, and to see if there are any variations in reaction time between the two temperatures. The study! also focuser on whether different sitings affect t he adjustment time when the warm front arrives and if the time of arrival i s important for the resulting temperature variations. The results show that weather preceding the front, temperature difference when the front arrives , arrival time of the front, wind speed and the occurrence of precipitation all have an effect on the adjustment time. Air temperature reacts faster t o a weather change than the road surface temperature. During the evening th e road surface temperature can still be affected by previous shading for up to four hours after a front arrival. When the total cloud cover increases above 4 oktas before noon there dl-e no or small lags in reaction time betw een air and road surface temperature, since there is insufficient time to e stablish shading effects.