All about Humidity

• Humidity measures the amount of water vapor in the atmosphere.
• High humidity and temperature create muggy conditions because water vapor retains heat.
• Warm air has a greater capacity to hold moisture.
• Low humidity results in drier air, like in deserts or on cold winter days.
• Humidity is important in weather forecasting as it indicates the water vapor content in the air.

Humidity Measurement

• Absolute humidity is the density of water vapor in a parcel of air (mass of water vapor/volume of air).
• Absolute humidity is not often used in forecasting because its dependent on air volume, which changes with air pressure.
• Relative humidity is the ratio of water vapor in the air compared to the maximum it can hold at a given temperature and pressure to achieve saturation.
• Air parcel saturation occurs when evaporation and condensation are balanced.
• Relative humidity = water vapor content/water vapor capacity, and is multiplied by 100 to get a percentage for forecasting.
• Relative humidity is important for weather forecasts and maintaining balance in buildings.
• Too much indoor moisture can cause structural damage and mold.
• Too little indoor moisture can cause dry skin and increased static electricity.
• Dew point temperature is the temperature to which air must be cooled to reach saturation, without changing air pressure or moisture content.
• When air at ground level reaches dew point and the surface cools, dew forms.
• When this process occurs away from the surface, clouds form.
• Dew point temperatures are critical in weather forecasting, and are directly related to the amount of water vapor in the air.
• High dew points indicate high water vapor content, and low dew points indicate low water vapor levels.
• Dew points between 50-60°F are comfortable for most.
• Dew points around 65°F feel sticky.
• Dew points between 65-70°F are unpleasant.
• Dew points above 70°F can feel oppressive, especially for those with health conditions.

How Humidity Works

• The amount of water vapor in the air influences weather patterns.
• The water cycle drives humidity, beginning with the sun heating the oceans and starting evaporation.
• Water evaporates from oceans, lakes, streams, ice, and puddles, becoming water vapor.
• More water vapor in the air results in higher humidity.
• Wind moves water vapor, which condenses to form clouds.
• Clouds may produce precipitation depending on temperature, pressure, and moisture content.
• Precipitation returns water to the Earth, restarting the cycle.
• Humidity regulates Earth’s temperature.
• Clouds absorb incoming solar radiation to keep the Earth cool.
• Clouds retain heat from the Earth to keep it warm.

Weather and Humidity

• Weather, climate, and geography are interconnected.
• Climate is the average daily weather over a long period in a specific region.
• A geographical location's climate, such as proximity to oceans, mountains, and latitude, drives daily weather.
• Humidity is higher near oceans compared to the leeward side of mountains.
• Warm tropical regions hold more water vapor, resulting in high humidity.
• The southeastern United States experiences high humidity during summer.
• The southwestern United States has low humidity due to limited water vapor.
• Arid climates (southwest US) have more evaporation than precipitation.
• Comfortable indoor relative humidity ranges between 30%-60%, with optimal comfort between 30%-50%.

Humidity is the measure of water vapor in the air and is important in weather forecasting. Relative humidity measures the amount of water vapor relative to the maximum the air can hold. Air parcel saturation occurs when evaporation and condensation are balanced.