During the summer in Washington DC, humidity can make even the most beautiful days feel oppressive. It can cause fatigue, muscle cramps, heat stroke and even damage your home if left unchecked.
A city's relative humidity is measured by how much water vapor it can contain in the air compared to a certain temperature. It is dependent on both moisture content and temperature but in general, a city's relative humidity will be lower during the winter than in the summer.
The highest relative humidity ever recorded was 95degF at Dhahran in Saudi Arabia in 2003 making 42 degrees Celsius feel like 81°C! Most cities have a limit of around 30-40% relative humidity, and Washington DC is no exception.
Temperatures vary from season to season and from day to day depending on weather patterns, with the hottest months of July and August having average temperatures of 80degF to 88degF (26degC to 31degC). The coldest month is January with an average of 41degF to 26degF (-5degC to -3degC).
The majority of rainfall in September occurs in waves. Heavy rainfall of 0.5 inches (13mm) or more typically occurs on only two to three days during the month, with clear or mostly sunny skies occurring about 60% of the time.
The best way to beat the heat in DC is to stay indoors where it is cooler, and ideally, use AC! It’s also a good idea to dress light and pack an umbrella for the occasional showers.