Over a month’s-worth of rain could fall in the Desert Southwest as former Hurricane Priscilla juices up the atmosphere

By CNN Meteorologist Chris Dolce

(CNN) — A notable flood threat is on tap for some of the driest areas of the United States as an ailing former Hurricane Priscilla combines with another storm system to create a long-lasting rainfall event.

More than an October’s worth of rain could fall within days in some areas of the Southwest as the week comes to a close. And another tropical system following on the heels of Priscilla early next week could pile onto the flood threat.

It’s all happening in part because Priscilla, now a tropical storm, will juice up the atmosphere over the Southwest US with near-record levels of moisture for this time of year.

Think of the amount of moisture in the atmosphere like the amount of water in a sponge. The more there is, the more that can be wrung out by storms.

Priscilla is expected to dissipate later this week to the west of Mexico’s Baja California Peninsula. However, its moisture-rich air will get scooped up by a weather system riding through a dip in the jet stream along the West Coast.

This is a classic weather pattern that has historically been responsible for slingshotting Eastern Pacific hurricane remnants into the Southwest US where they can trigger flooding rain.

Periods of rainfall will likely begin to increase Thursday and Friday from Arizona and southeast California to the Four Corners region. The heaviest soaking could peak late Friday and Saturday.

The heaviest bands of rain could produce flash flooding, particularly in low-lying areas. Washes, small streams and creeks and slot canyons could fill with rushing water, so it’s best to avoid these areas.

Rainfall totals could be more than the entire October average in some areas.

It’s possible Phoenix tops its average October rain of just over a half-inch in a day or two. Flagstaff would need an inch and a half of rain to meet its average for the month.

That might not sound like much, but it can create serious problems in the desert where water runs off the dry ground quickly, especially if it falls fast enough. About 2 inches of rain fell in 30 minutes in Globe, Arizona, late last month, sending a torrent of water into downtown that swept cars away, damaged buildings and killed three people.

Phoenix is coming off its 10th-wettest September after picking up 2.26 inches of rain, or nearly quadruple the month’s average. Much of that fell during the same storm system that caused the deadly flooding in Globe. Despite the recent drenching, the Valley of the Sun remains in severe to extreme drought.

The higher elevations of northern Arizona are likely to see the heaviest totals, possibly up to 3 or 4 inches.

A Level 2 out of 4 threat of flooding rainfall is in place for Friday and Saturday in parts of Arizona, northwest New Mexico, southeast Utah and southwest Colorado, according to the Weather Prediction Center.

This might not be the end of the tropically-infused wet Southwest pattern either. Another Eastern Pacific tropical system could bring a new burst of drenching rain Sunday into Monday.

The heaviest rain from this second round might fall a bit farther east from southeast Arizona, including Tucson, into New Mexico, but details are still uncertain.

The-CNN-Wire
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