Western rainfall to bring drought relief, increase flood risk
Flooding and mudslides have been common in the Southwest since Tropical Storm Kay brought an increase in moisture to the region last week. AccuWeather forecasters say that more drenching rain is on the way.
After a brush with Tropical Storm Kay over the weekend, parts of the southwestern U.S. got even more rain on Sept. 12, leading to dangerous mudslides in some areas.
After days of scorching, record-shattering heat in the western United States, cooler air has filtered in along with daily showers and thunderstorms across the region. AccuWeather forecasters say that more of the same is expected through the rest of this week, even as the exact location of these storms may shift around from day to day.
This stretch of wet weather began late last week, with rain from Tropical Storm Kay dousing much of Southern California, and leading to issues with flooding and mudslides. Meanwhile, a surge of tropical moisture associated with the North American monsoon overspread much of the Intermountain West, bringing daily showers and thunderstorms across the region.
Not every location across the West has had storms on a given day, but storms that have formed have often been intense, bringing heavy rainfall and strong wind gusts to some locations.
In Phoenix, storms arrived late Sunday evening. Along with a quick 0.62 of an inch of rain in the city, damaging wind gusts reached as high as 86 mph at Sky Harbor International Airport, one of the busiest airports in the country, prompting a ground stop that caused flights to be delayed and rerouted.
Las Vegas set a daily rainfall record on Monday when a total of 0.17 of an inch fell. The previous daily rainfall record for Sept. 12 there was 0.05 of an inch, which was set back in 1969.
Elsewhere, bursts of heavy rain caused a different array of issues in the mountainous terrain of California. As rain fell and turned the dirt on mountain slopes to mud, huge debris flows were seen in some locations, including in the Southern California city of Yucaipa, located just southeast of San Bernardino, where an enormous, slow-moving mudflow covered a roadway near a steakhouse. The Yucaipa Police Department issued an evacuation order for parts of the area, which is located near the 2020 Apple and El Dorado Fire burn scars.
Some evacuation and shelter-in-place orders were issued due to mudslides for thousands of residents in other parts of Southern California on Monday, The Associated Press reported. Structural damage to several buildings was reported in the community of Forest Falls, located about 75 miles east of Los Angeles, but no injuries were reported, according to the AP.
A slight change in this pattern may affect where the threat of showers and storms occurs on Thursday. This will allow some places to dry out as other locations get their first chance of rain in a lengthy period of time.
"This will finally allow California to dry out after an exceptionally wet month so far, but put the Rockies and High Plains in play for these storms," Geiger added.
The dew point temperature is a measurement of how much moisture is present in the air. Across the Southwest, these values have hovered in the 50s or higher, which means there's enough moisture to allow thunderstorms to develop.
However, as this moisture begins to shift eastward, the dew points across California will struggle to leave the 30s and 40s, which is usually too dry for thunderstorm development.
The opposite scenario is set to occur across the Rockies and portions of the Plains, with dry air being replaced by more humid conditions.
As is typical for monsoon-driven showers and storms, the coverage will be somewhat isolated. Some spots may stay dry on a given day, but others may receive rounds of heavy rainfall and perhaps strong wind gusts. In the locations that receive the heaviest rain, flash flooding may become a concern. This is especially true in areas with mountainous terrain, as runoff can funnel into low-lying valleys and cause water levels to rise in a matter of minutes, forecasters say.
The increase in rainfall may prove beneficial to the ongoing drought, which still covers most of the Southwest, according to the U.S. Drought Monitor.
The chance of rain may also prove beneficial to firefighters, with numerous wildfires ongoing across the Intermountain West. Even a brief period of rain can substantially slow a fire down and allow crews to contain it faster. However, the storms can also be a double-edged sword as lightning strikes in dry locations can cause separate fires to develop. Gusty winds generated by storms can also cause erratic changes in fire behavior.
The wet, humid pattern is expected to continue through most of the week in the West. By the weekend, a return to drier weather may be in store.
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