Question of the Day - 17 August 2023

One can never predict the exact weather with any certainty, of course, especially given the lead time required to plan a trip to Las Vegas. However, the possibility of seeing a Southwestern-desert electrical storm can be narrowed down to a roughly 10-week period: July 15-Sept. 30. The worst (or best, given your point of view) of it, however, is confined to the six weeks from mid-July to the end of August. 

The storms occur as a result of the North American monsoon, which has been called "perhaps the most regular and predictable weather pattern in North America." It gathers steam in late May in southern Mexico and spreads into the southwest U.S. by mid-July. It supplies up to half of the annual precipitation in Arizona and New Mexico and affects weather patterns from California to Utah, from Texas to Colorado.

The cause of the North American monsoon is a subtropical-ridge high-pressure zone that moves northward during the summer months and converges with a thermal low over the Southwest U.S. and northwest Mexico. In other words, moisture-laden currents of air blowing inland northeast from the Gulf of California and northwest from the Gulf of Mexico collide with a wall of hot dry desert air. However you define it, the monsoons are characterized by spectacular lightning activity and torrential thunderstorms.

In Las Vegas, the storms, foreshadowed by towering cumulonimbus clouds with dark flat bases boiling up over the valley, embody the worst weather that southern Nevada experiences. During the height of it, the National Weather Service's sophisticated and sensitive lightning-strike monitoring equipment can’t keep up with the onslaught of atmospheric electrical activity.

But it's the torrents of rain that cause most of the trouble in Las Vegas. Record rainfall was recorded in 1955, when three inches inundated the valley in 60 minutes. In 1975, a famous flood washed away 300 cars from the front parking lot of Caesars Palace (prompting city officials to begin planning the valley's flood-control system, which is covered in passionate detail in our book Beneath the Neon -- Life and Death in the Tunnels of Las Vegas).

Two back-to-back storm systems in August 1981 unleashed seven inches of rain in less than three hours on Moapa Valley, about 45 miles northeast of Las Vegas.

A severe thunderstorm in August 1997 dumped heavy rain near Page, Ariz., sending a 50-foot-high wall of floodwater thundering down Antelope Canyon and killing 11 hikers who were touring the narrow canyon that drains into the Colorado River.

The Regional Flood Control District's Gowan North Detention Basin can fill with 12 feet of water in 15 stormy minutes.

In short, these storms are almost otherworldly in their beauty and fury. Just make sure you're in a safe place when one hits.