Flooding rain, severe thunderstorms shift to interior West into Friday
A storm responsible for areas of rain and thunderstorms and severe weather through midweek over the Southwest will focus its efforts farther inland over the western United States into Friday.
A motorist and her passenger were audibly terrified as they watched large hail smash the windshield of this vehicle during a severe storm in Phoenix, Arizona, on Oct. 21.
A large storm will continue to slowly spin through the interior western United States through the end of this week. The storm will bring beneficial rain to drought-stricken areas and help lower wildfire threats, but it will also raise the risk of flash flooding, mudslides and severe thunderstorms.
Several rounds of rain will be associated with the massive setup, with rain beginning to shift well inland from the West Coast to parts of the Rockies. A small amount of tropical moisture from Trudy may also become involved over the interior Southwest.
"The timing of the heaviest rain in Southern California is expected to be into the first thing Thursday morning," AccuWeather Senior Meteorologist Adam Douty said. "The storm will bring a general 0.50 to 1 inch of rain to low-elevation coastal areas of Southern California with heavier rain, averaging 1-2 inches on the south- and west-facing slopes of the hills and mountains in the region."
Mudslides and other debris flows can occur in any steep terrain, but areas that have recently experienced wildfires will face a much higher risk.
The wettest period around Las Vegas and Phoenix is likely to be through Thursday when multiple downpours are possible. Downpours in urban areas and deserts can lead to dangerous flash flooding. Normally dry streambeds and drainage basins can rapidly become raging rivers.
"Las Vegas has already picked up nearly four times their historical average rainfall for October with 1.19 inches falling through Tuesday, before the storm arrived," Douty said. "This storm will only continue to add to that departure from average."
The showers and thunderstorms are likely to push eastward into parts of New Mexico and Colorado through Thursday as well, but they may also persist on Friday.
At least sporadic showers and storms will linger over the interior West into the weekend.
The same setup will bring a risk of severe weather on Thursday, with the greatest risk of storms packing high winds and hail, along with flash flooding, being over the interior Southwest.
After bringing damaging winds, hail and even a tornado or two on Wednesday, the threat will expand northward and eastward Thursday, reaching southern Utah and western New Mexico, while continuing in central and eastern Arizona.
Meanwhile, along the coast of Southern California, a few embedded thunderstorms will pose the risk of producing a couple of brief waterspouts and tornadoes into early Thursday.
The risk of severe weather on Friday and Saturday will be focused largely on New Mexico.
Since part of the storm setup involves a large dip in the jet stream, which is associated with chilly air in the upper levels of the atmosphere, some snow will fall over the ridges and peaks of the Sierra Nevada. While some wet snowflakes can mix in from time to time, no snow accumulation is anticipated over the passes.
The large storm with vast areas of rain will bring another round of runoff into the Colorado River basin. It will take much more rain than this storm can provide to ease the historically low water levels, but the impending rain will help somewhat in the short term.
Water levels have risen about 5 feet from their lowest level on Sept. 16 on Lake Powell, while water levels continue to fall farther south along the Colorado River basin at Lake Mead.
It will take a winter full of storms with heavy mountain snow to significantly raise water levels during the subsequent spring thaw due to vast areas of extreme to exceptional drought in the region.
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