On Saturday, July 31, 1976, several hundred tourists and locals were enjoying a beautiful summer afternoon in the resort town of Estes Park in northern Colorado. A stationary front (when warm and cold air masses meet and neither is strong enough to move the other) had settled in an east-west fashion across Colorado, Kansas, and Missouri. Warm, moist air was forced up the Front Range and the unstable air continued rising as the water vapor condensed, becoming conditionally unstable (where the air is unstable if saturated but stable if saturated).
Light rain began falling over the Colorado Rockies during the late afternoon. By 7:35 p.m., the National Weather Service had issued a severe thunderstorm warning. Around 9:00 p.m., the National Weather Service issued an urgent warning to expect flooding in the Big Thompson Canyon, but the warning came too late for most. At this point, 12 inches of rain had fallen within the last four hours and sent a 20-foot wall of water down the narrow canyon, causing flood waters to speed up as they squeezed through. (According to the Bernoulli principle fluids speed up as they are forced through a tight space due to an increase in pressure). Weaker winds aloft made the thunderstorm nearly stationary near the upper section of the canyon.
Rex Sheets of Loveland, Colorado was driving with his friend up towards Lake Estes to go fishing on July 31st. A state patrolman began driving up the canyon during the early evening hours to warn others of the storm. The frame of his car was later found with the steering wheel attached and his keys still in the ignition. The patrolman’s body was never recovered.
The amount of rain that fell in that short amount of time made it so that the rain wasn’t able to soak into the canyon sidewalls. Boulders the size of cars were carried down the river by the floodwaters and houses were transported on top of bridges. The flood caused $35 million in damage, destroyed 418 homes, and claimed the lives of 143 people.
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© 2017 Meteorologist Sharon Sullivan