The weather conditions can have a considerable effect on sound level readings, for a number of reasons. Two of the most significant influences are wind and rain. You can read a little bit of information below that explains how changes in weather can influence sound level readings, particularly at unmanned stations.
During manned surveys measurements are not usually taken in high winds. This is unavoidable during permanent monitoring and we have to consider the influence of wind on the measured sound levels. In high winds, greater than 5 m/s or 18kph, sound level measurements can be affected by wind noise at the microphone. A windshield can reduce the influence of wind noise, however, at higher wind speeds the recorded levels will include a certain amount of noise attributed to the wind. This will lead to an increase in measured levels, making readings higher than if the sound source (busy road) was measured in calm conditions. Also, in particularly windy conditions, reception of the sound at the sensitive locations can also be blocked or reduced by wind noise at the property. The average daily wind speed for the local area is displayed on our calendar view to provide extra information in support of the sound level readings. Where the wind speed is very high we know that this should be factored in if the readings are much greater than usual.
Rainy days are generally louder for a number of reasons. The first major influence the rain has is to increase the noise that vehicles make on the road. Tyres on a wet road produce more noise than on a dry surface. There are several technical causes for this to do with how the tyre, road, water and air all interact. But the effect is the same, the sound level readings on wet days go up.
This is not the only effect that rain has. A wet day also leads to changes in travel patterns. More people tend to drive to work, meaning more cars making noise. Traffic also moves in a slightly different way, caused by increased congestion and different traffic speeds than on dry days. This has a knock-on effect on sound level readings. All these factors must be taken into account when comparing one sound level reading with another.