High Dew Points Increase Severe Weather Chances

URBANA – Severe weather often occurs in March with dew point temperatures in the 50s or 60s. Duane Friend, University of Illinois Extension natural resources educator, explains the impact of dew point on weather.

Water vapor is the gas form of water. Air can only hold so much water vapor. When air reaches a temperature where it is holding as much water vapor as it can hold, the air is said to be saturated. The temperature at which this occurs is called the dew point temperature.

"A more common way of talking about dew point is when relative humidity is at 100%," Friend says. "Warmer air can hold more water vapor; cold air can’t hold as much."

When dew point temperatures are low, the air is not holding much water vapor. Higher dew points mean more water vapor is present.

"Water vapor heats the surrounding air when it condenses," Friend says. "High dew points can increase the chances of thunderstorms."

What conditions may increase the chances for thunderstorms?

March is a big transition month from winter to spring. Warm air masses from the Gulf of Mexico start pushing into the state, raising the dew point temperature.

"That, by itself, doesn’t cause thunderstorms, but if there is a strong cold air mass that moves in and wants to move to higher elevations, that warm air will quickly cool to the dew point temperature as it moves upward, condense to liquid water, release heat and have an even greater tendency to move upward."

Thunderstorms often form under these conditions, Friend says.

"If you see dew points in March in the 50 to 60 degree range, that indicates a lot of moisture in the air. In turn, the chances for thunderstorms are pretty high."

As the air naturally warms during April and on into summer, normal dew points will get into the 50- and 60-degree range, and those readings won’t be a problem.

SOURCE: Duane Friend, Illinois Extension Natural Resources, Environment, and Energy Educator

ABOUT EXTENSION: Illinois Extension leads public outreach for University of Illinois by translating research into action plans that allow Illinois families, businesses, and community leaders to solve problems, make informed decisions, and adapt to changes and opportunities.

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