Maryland Weather Meteorology, astronomy and climate conditions in the Baltimore region

The humidity in Baltimore is 'oppressive.' Here's why it feels so muggy.

“Oppressive” is the word even meteorologists use to describe the humidity that has returned to the Baltimore region this week.

They measure it using a statistic known as the dew point, calculated using a formula that factors in both temperature and humidity to express just how muggy it feels outside. Dew points up to about 55 degrees feel dry and comfortable; from about 55 to 65 degrees, it starts to feel uncomfortable.

The dew point Tuesday morning was as high as 75 degrees — a level of moisture meteorologists actually classify as oppressive.

The dew point is a more nuanced measure of humidity than just relative humidity because warmer air holds more moisture than cooler air. So factoring in both temperature and moisture is a better way to express how it feels — 100 percent relative humidity at 40 degrees doesn’t feel the same as 100 percent humidity at 75 degrees.

But why does high humidity make it feel hotter than a desert?

The body cools itself through sweating — it literally releases heat through liquid sweat, which evaporates into the air. But when it’s humid out, sweat doesn’t evaporate as quickly or as much, hindering that cooling system.

Last week brought a break from the humidity, with dew points dropping well into the 50s for the first time in weeks, if not months.

But summer isn’t done yet — dew points are forecast to hover in the 70s through this week and the weekend.

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