It’s that time of the year where the monsoon has kicked into gear. That means several things, noticeably higher humidity, heat of the day thunderstorms, and flash flooding.
Our monsoon occurs when high pressure at ground level strengthens over the Central and Southern Plains and returns a southerly flow into the Mountain West. Along with this high pressure, a broad area of low pressure develops from Arizona and into Nevada as intense summer heat dominates through the mid to late summer months also strengthening the southerly wind flow that actually picks up water vapor out of the Gulf of California, and delivers this humid air into Utah. Add in highly humid air to our hot state, and you produce thunderstorms.
The storms form during the heat of the day as rising air currents develop from the heating ground and vertical columns of rising air are created, or convection. With such highly humid air, these thunderstorms can produce vast amounts of rain that can fall at rates of upwards of 1”, 2”, to 3”+ amounts of rain per hour.
“Millions of gallons of water”
That’s millions of gallons of water that needs to go somewhere, and on hot dry ground that means is flows downhill and towards the lowest location. For Southern Utah, this water quickly flows into normally dry stream beds (washes) along with canyons, and very narrow steep canyons such as the slot canyons in Zion National Park.
This video shot in 2013 by David Rankin shows just how quickly the floods move.
This water flows very fast, and it doesn’t take but up to just a half a foot of fast flowing water to knock you off of your feet, and up to about 2 feet of water can lift and wash away your car.
Unfortunately Utah is all too aware of the dangers of flash flooding when a dozen people lost their lives as their cars were swept away by flash flood waters. And in the same storms, seven hikers also died hiking slot canyons in Zion National Park in 2015 as quickly developing storms produced the deadly flash floods.
Sometimes cell coverage is not available in the more rural areas of Utah including the National Parks and monuments. So besides having your ABC4Utah Pinpoint Weather App handy, also have a portable N.O.A.A. weather radio, such as these from Midland Radio. And the radio signal coverage WILL alert you of any immediate weather warnings to inform you of potential danger.