Latent Heat

In Colorado, July is known for its frequent thunderstorms. Meteorologists often refer to dew point and relative humidity when discussing the chances for thunderstorm activity. The higher the dew point and humidity, the greater the likelihood of showers and thunderstorms. When the dew point exceeds 50 degrees Fahrenheit along the Front Range, the chances for heavy to severe thunderstorms increase significantly.

The reason for this correlation between moisture and storm severity is due to a phenomenon known as latent heat energy. Latent heat energy is the heat and energy stored in water vapor, the gaseous form of water. When liquid water is heated, it turns into water vapor, and the heat energy is stored in the vapor. This process of evaporation occurs naturally in the environment, as water evaporates from bodies of water and even from the ground.

When humid air rises, it cools and eventually reaches a point where the water vapor condenses back into liquid form, releasing the stored heat energy in the process. This release of heat energy can fuel the growth of thunderstorms, allowing them to grow taller and stronger. The more water vapor that is converted back into liquid form, the more energy is available for the developing storm to use.

Along the Front Range, the air is typically quite dry. For example, during the month of July, a typical dew point at Denver International Airport may be 35 degrees Fahrenheit, with a relative humidity around 13%. Further east, in Limon, the dew point can easily reach 55 degrees Fahrenheit, with relative humidity around 35%. This is a common pattern, with moisture levels increasing further east onto the plains. As a result, storms that form along the Front Range may initially be weak, with gusty winds and some lightning, but little rain. These storms are known as Dry Thunderstorms. However, as they move east and tap into the higher moisture levels, they can grow in strength and severity.

In summary, the more moisture that is available in the air, the more heat energy a developing storm can tap into and use. This is why high humidity days are often associated with a greater chance of heavy to severe storms.

To learn more about thunderstorm development, visit the UCAR learning page about thunderstorms here: https://scied.ucar.edu/interactive/make-thunderstorm

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