Monsoon storms to be double-edged sword in southwestern US into the weekend

Showers and thunderstorms will help ease drought conditions in the southwestern United States into the weekend, but also enhance the risk of flash flooding and dust storms.

“Monsoonal moisture will remain in place from part of Southern California to Colorado and New Mexico,” said AccuWeather Meteorologist Jordan Root.

Moisture will continue to stream into the region through the balance of the week.

As is typically the case when the monsoon kicks in at this time of year, storms will tend to blossom over the highest terrain during the afternoon hours and drift toward lower elevations into the evening and overnight.

While the region could use a thorough soaking with widespread extreme to exceptional drought ongoing, the storms through the week can drop too much rain in a short period of time, which can create flooding dangers.

“These storms can bring flash flooding, debris flows and mudslides,” Root said.

On Sunday evening, severe flash flooding occurred northwest of Tucson, Arizona, in Pima County, with video captured by AccuWeather Extreme Meteorologist Reed Timmer showing some motorists driving through the floodwaters.

On Monday evening, both Phoenix and Las Vegas were impacted by haboobs and heavy thunderstorms, resulting in low visibility, flooding, closed roads and airport delays.

It is never a good decision to risk your life, the lives of other passengers and your would-be rescuers by driving through floodwaters.

“It's impossible to tell how deep the water is and the roadway underneath may be compromised,” said AccuWeather Meteorologist Faith Eherts.

Six inches of rapidly flowing water is enough to knock a person down and 12 inches of water can float most vehicles.

“This weather pattern can also pose a serious threat to hikers and campers,” Eherts said.

Dry creek beds, known as arroyos, can suddenly fill with water due to a heavy thunderstorm upstream, overflow and flood neighboring roads and lands.

Those hiking in the mountains should plan to head out early in the morning and return by midday to avoid the bulk of the storms. Be watchful for rapidly growing and darkening clouds, which can be a sign that a storm is brewing.

If thunder is heard or lightning is seen, head immediately downhill to a valley or depression in the terrain.

Gusty winds blowing out from the storms will create further hazards by possibly generating dust storms, according to Root.

Motorists should pull over on the side of a road with emergency flashers on if a dust storm envelops the roadway, as visibility can quickly drop to near zero and heighten the risk of multi-vehicle pile ups.

If the dust storm becomes too severe, some roads may be closed for a time, as was the case along Interstate 10 near Casa Grande, Arizona, on Sunday night.

The thunderstorm winds can also be high enough to snap trees and power lines.

Root expects thunderstorm activity to be not quite as widespread this weekend, mainly confined to Arizona, New Mexico and Colorado.

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