“A multi-day significant rainfall event is forecast across the Southwest US this weekend,” the Weather Prediction Center said. “Impactful rainfall is most likely across parts of southeast Arizona into southwest New Mexico with storm total amounts approaching 5-6 inches.”
Flood watches are posted for nearly 10 million people across the Southwest, including Tucson, Phoenix, Albuquerque, and El Paso, through Saturday.
Zack Taylor, a senior meteorologist at the Weather Prediction Center, pointed out there are multiple factors creating the new surge of moisture, including the remnants of a tropical wave currently over northern Mexico embedded within the larger-scale monsoon.
One thing making the particular event different is the timing of the storms. Typically, monsoon storms are diurnally driven, meaning they occur in the afternoon and early evening. This time, the chance for rain will be around the clock. Storms will fire up in the afternoon and early evening as usual, but will also occur Friday overnight and early Saturday morning.
There are also two time lines as far as the impact goes with the next system: the short term, which would be flash flooding, and the long term, which would be the influence on the rivers, creeks, and streams in the area.
“The main concern is with the flash flooding initially,” Jeff Davis, senior meteorologist for the National Weather Service office in Tucson told CNN. “But we’re transitioning into a situation where we may have some of the larger washes that are normally dry and some of the main stem rivers starting to see significant flows by Monday.”
Monsoon rains are helping the drought, but not enough
While the desert Southwest may not be known as a wet part of the country, this time of the year is when it is most likely to get rainfall. The rainy season helps the Southwest, but it often leads to superficial improvement.
One of the concerns with the upcoming heavy rain is it is not expected to surge far enough north or west where the water is needed most: California, Nevada, Oregon, and northern Utah.
The recent rains have helped, but only for some areas of the West. Roughly 70% of the West is still in some level of drought, down from 90% just three months ago. Most of the improvements have been in just two states, Arizona and New Mexico. The recent rains have helped those two states even more.
“Monsoonal rains are only a fraction of the water needs of the West,” said Chad Myers, CNN meteorologist. “That said, the recent rains have raised the level of Lake Mead by 1.8 feet over the past three weeks.”
Myers pointed out the main driver for water in this region is the melting winter snowpack, but it doesn’t mean the rainfall isn’t beneficial.
“Although the heaviest of the upcoming rain will miss the Colorado River basin and Lake Mead, plenty will still fall in Utah and Colorado directly into the upper drainage basin of the river,” Myers said.
The US Southwest monsoon officially runs from June 15 to September 30, putting the region beyond the halfway point of the season.
Salt Lake City has had 6.70″ so far this year, but their average is more than 10 inches. It is an ever-present sign of how bad the drought has been over the last few decades in the region that we are celebrating getting a little more than half of what is normal.
CNN Meteorologists Pedram Javaheri and Tom Sater contributed to this story.