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Dangerous California storm to hammer southwestern US, including Las Vegas and Phoenix

The same storm responsible for torrential rain, life-threatening flash flooding, high winds and mountain snow in California is swinging slowly inland over the southwestern United States into midweek. Soon after heavy rain raises flooding concerns in the deserts, heavy snow will pile up over the mountains in Nevada, Arizona, Utah, New Mexico and Colorado, AccuWeather meteorologists warn.

Heavy rain on the desert landscape is notorious for rapid runoff and dangerous flash flooding, mudslides and other debris flows. This highlights the concern among forecasters for the interior Southwest over the next few days.

Even though the atmospheric river, or firehose of rain, that blasted Southern California on Monday is in the process of weakening as it progresses inland, enough will remain intact to bring periods of heavy rain to the deserts of the interior southwest United States, AccuWeather Meteorologist Joseph Bauer said.

"The flash flood risk will not nearly be as widespread as that facing California, but even localized flash floods will pose risks to lives and property in Arizona, Nevada and other locations in the Southwest into Thursday," Bauer stated.

The flash flood risk includes the major cities of Las Vegas and Phoenix. The heaviest rain will hit Phoenix through the daylight hours on Wednesday, while Las Vegas will be most affected by heavy rain late Wednesday night.

"While even a quick downpour can lead to street and highway flooding in the region, the heaviest rain, from 1-2 inches, is most likely to occur on the south- and southwest-facing mountainsides in Arizona," AccuWeather Senior Meteorologist Adam Douty said.

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The risk of debris flows will be greatest in, but not limited to, recent wildfire burn scar locations. Normally, dry stream beds, called arroyos by locals, may suddenly fill with rushing water, similar to what can happen during the summer with monsoon thunderstorms.

Many low-elevation cities and towns over the desert Southwest average under an inch of rain for February.

As the storm pivots across the interior Southwest, it will trend colder, and snow levels will lower substantially. From several inches to a couple of feet of snow will pile up over the ridges, peaks and plateaus in the region.

At an elevation of 6,800 feet above sea level, Flagstaff, Arizona, will be buried under 18 to perhaps 24 inches of snow, most of which will fall through Wednesday. Segments of Interstate 40, which runs from west to east across the state, will face heavy snowfall rates and the risk of road closures.

As the atmosphere trends colder, temperatures may dip enough to allow some wet snowflakes to mix in with the rain at times around Las Vegas into Thursday evening. The most likely time for these to occur would be first thing Thursday morning, local time.

Farther to the north, around Salt Lake City, periods of a rain and snow mix are in store from the storm into Thursday. However, on the benches to the east of the city and in much of the Wasatch Range, snow will pile up with road closures, possibly along portions of Interstates 70 and 80 over the Rockies.

Most of the storm's moisture will move to the west of Denver. Conditions will be too warm for snow in Albuquerque, New Mexico, but several inches of snow are likely to pile up in the mountains in northwestern New Mexico.

Looking ahead, a couple of smaller, weaker storms will pivot in from the Pacific Ocean from midweek to this weekend.

"Since these storms will trend to be even colder than the storm at midweek, snow levels will dip even lower over the interior Southwest so that some intermediate and low elevations may pick up accumulating snow," Bauer said.

Even though these storms are not likely to contain an atmospheric river, pockets of soaking low-elevation rain and heavy mountain snow are likely over the interior Southwest. As a result, periodic travel disruptions are likely from mountain snow, with highly localized flash flooding being an ongoing concern.

The storms will likely pivot away from Las Vegas this weekend for events leading up to the big game on Sunday.

The drier pattern for the southern Nevada metro area may evolve quickly enough for fans to walk the Las Vegas Strip without concerns about getting wet on Saturday. However, travel issues due to rain episodes may occur from Tuesday to Friday. High temperatures around the city will be in the 50s for much of the week.

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