Indoor radon concentrations in northern Virginia and central Maryland show a strong dependence on weather. Winter tends to be associated with higher than average indoor radon, and summer with lower than average. However, compared to the winter of 1986–1987, the winter of 1987–1988 was warmer and drier. Consequently, winter‐to‐winter indoor radon decreased by about 25%. This winter‐to‐winter decrease is unexpectedly large, and simulates winter‐to‐summer variations that have been reported.