The main concrete parameter influencing the corrosion rate of rebars when they are depassivated is the moisture content of the concrete. In concrete structures exposed to outdoor atmospheres, this depends on the climatic cyclic variations of relative humidity and temperature which continuously change during the day and night and with seasonal variations. The corrosion rate also changes but the value recorded at a precise moment may not correspond to the actual hygrometric situation. This makes the implementation of corrosion rate values measured on-site into predictive models difficult, and calls for more detailed studies and statistical treatments. In this paper changes in the corrosion rate in concrete structures submitted to outdoor exposure and not sheltered from rain are monitored. More detailed measurements were made during certain periods. Simultaneous recording of temperature, relative humidity, resistivity, corrosion potential and corrosion rate enabled changes in the complexity of interacting processes to be followed. Some specific trends are identified from which it can be deduced that the seasonal changes in temperature control the main parameters involved, although a general relation between temperature and corrosion rate could not be found.