High Summer Humidity in Colorado = Thunderstorms

My son, in his first days as a freshman at Colorado State University, overheard some kids from Washington State commenting on how they loved the dry heat. He laughed. Yesterday was one of the most humid we’ve had in a humid-for-Colorado summer.

4:00 8/22/13 50%

50% relative humidity — a lot of water in the air for Colorado — completely hides downtown Denver from Green Mountain.

How humid was it? At 4:00, when it is usually about 10-15% humidity, it was 50% — unheard of!

I took this picture yesterday from Green Mountain just west of Denver to show the grey, water-soaked air. Very hazy.

The humidity turned into thunderstorms later in the evening. We got about an inch of rain on Green Mountain. At Denver International Airport (DIA), they broke a record, enduring a pounding 1.97 inches of rain, more than an inch over the old record of .75 inches.

8/23/13 3:00 27% humidity.

A still soggy 27% humidity reveals Denver in the distance.

For comparison, here’s a photo I took today at about the same time in the afternoon. The relative humidity here is 27%, but you can at least see downtown Denver. On a more typical day, the city is even more clear.

Colorado Monsoons

The weatherman is calling for thunderstorms tonight, as “monsoon moisture returns to the state.”
I always feel weather forecasters are a little presumptuous calling summer moisture in Colorado monsoons.  I mean, although we can have the occasionalImage gully-washer, our piddly precip is nothing compared with the six months of torrential rain that most people normally think of when they hear the word monsoon.
But according to weather people, “a monsoon is a wind that changes direction with the seasons”. By that definition, the Southwest, with Colorado on it’s northern edge, has a monsoon.  Summer heat on the desert of Southwest Arizona, California, old and New Mexico warms the air there, causing it to rise.  This creates a vacuum, called a low Imagepressure cell.  The low pressure sucks moist air from the Pacific and Gulfs of California and Mexico, bringing storms to the west and southwest part of the state and

You can see the center of the low pressure system as a lack of clouds in Chihuahua Mexico. This system spun up into the Front Range of Colorado, where it dropped over half an inch of rain.

You can see the center of the low pressure system as a lack of clouds in Chihuahua Mexico. This system spun up into the Front Range of Colorado, where it dropped over half an inch of rain.

occasionally onto the plains. In winter, the Southwest deserts cool, and create a high pressure cell that can keep moisture out.
These summer storms don’t compare to the classic monsoons of Asia and east Africa, but Coloradoans are usually glad to get moisture in any form.