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Fox News Weather Center

Pacific Storm to Erase Heat and Deliver Rain to Los Angeles, Las Vegas and Phoenix

A cooldown with clouds, showers and thunderstorms are in store for Southern California and much of the Southwest following recent heat and sunshine.

A storm system is getting another chance at life over the Pacific Ocean this week. The system helped to bring some rainfall to California, Nevada, Utah, Colorado, Arizona and New Mexico earlier in the month, before it sank southward into Mexico and then drifted into the Pacific.

The cooldown for the Los Angeles and San Diego areas follows the longest-lasting heat wave of the year for coastal areas of Southern California.

Motorists should be prepared for slick roadways and travel delays on a regional basis in the southwestern United States. Some communities could be hit with a torrential downpours that unleash flash flooding.

The storm will pump more humid air into the Southwest during the balance of the week.

As humidity levels climb, so will the probability of showers and thunderstorms.

According to AccuWeather Senior Meteorologist Ken Clark, several days of unsettled weather may occur in areas that typically get little rain this time of the year.

"Scattered showers and thunderstorms can occur in Southern California from Wednesday afternoon through at least on Friday," Clark said.

Generally, a few tenths of an inch or less will fall along the coast of Southern California, but 1-2 inches are likely in the coastal ranges and the southern Sierra Nevada.

"There will be some exceptions to the rainfall in coastal Southern California and there could be enough in a few communities to cause flash flooding," Clark said.

Rain may stop short of Sacramento, California, initially, and is likely to miss San Francisco entirely through Friday.

"During the latter days of the week, showers and thunderstorms will expand into much of Arizona, southern Nevada, southern Utah, western New Mexico and southwestern Colorado," Clark said.

Cities likely to be affected by drenching downpours and the risk of flash flooding late in the week include Las Vegas; Phoenix; Albuquerque, New Mexico; Cedar City, Utah; and Durango, Colorado.

Some locations across the interior Southwest states may receive 1-3 inches of rain over a several-day period.

Rainfall has been above average every month since the start of the year in Las Vegas, and total rainfall has been above average since Jan. 1 for many areas outside of California. Even in drought-stricken Southern California, rainfall has been above average since the middle of the summer.

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A tremendous amount of rain is needed in California and much of the West to erase the drought conditions. Reservoirs have been shrinking and flows on rivers, including the Colorado and Sacramento, have been vastly reduced in recent years.

"During the weekend, another system from the central Pacific will move onshore and will spread showers throughout California, Nevada, and Utah as the potential for rainfall continues in New Mexico and western Colorado," Clark said.

While the rain this week and this weekend will stop well short of significant impact on the drought, it is likely to be another step in the right direction and a sign of what may be to come this winter.