What weather condition can increase indoor radon concentrations?

Heavy rain and high winds can lead to an increase in indoor radon concentrations due to the effects these weather conditions have on building pressure and the soil's permeability. During heavy rain, the soil becomes saturated, which can create changes in how radon gas is released from the ground. High winds may also affect the air pressure around the building, influencing the way radon enters through openings in the foundation or structures.

In contrast, sunny weather, cold temperatures, and dry air and clear skies generally do not create conditions that increase radon levels indoors. Sunny weather often leads to greater air exchanges between the indoors and outdoors, while colder temperatures can cause buildings to be sealed tightly, leading to reduced radon entry. Similarly, dry air and clear skies can also contribute to lower indoor humidity levels which traditionally would be associated with a reduced risk of radon accumulation. Thus, heavy rain and high winds stand out as conditions that can change the dynamics of radon movement and concentration indoors.