AccuWeather.com

By Kristina Pydynowski, Senior Meteorologist

Dec 22, 2010; 11:45 AM ET

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As evidenced in this video, flood waters turned the streets of Laguna Beach, Calif., into raging rivers early Wednesday morning.

The flooding situation is worsening across the Southwest, as the caboose of a relentless storm train swings inland through tonight. Strong thunderstorms threaten to create additional problems.

This last round of torrential rain will continue to inundate an area from central and Southern California to southwestern Utah and northwestern Arizona into tonight.

The ground across this zone is already extremely saturated following rounds of torrential rain that began last Friday. The latest soaking will only worsen the situation.

Governor Arnold Schwarzenegger declared a state of emergency in six counties of Southern California Tuesday due to the extreme weather conditions.

As AccuWeather.com Meteorologist Heather Buchman reported on Tuesday, this final storm in the series will send "rainfall totals for this entire event ranging from 5 inches to 2 feet in central and southern parts of California."

In addition to the heavy rain, snow will continue to pile up in the Sierra and the mountains outside of Los Angeles into tonight.

"It's not a matter of if more flooding occurs, it is how bad it will become," stated AccuWeather.com Western Expert Meteorologist Ken Clark.

Rivers and streams will rise farther out of their banks, threatening to wash away roads and bridges. Homes bordering these waterways are also in danger of getting destroyed.

Downtown Laguna Beach, Calif., suffered significant flooding early Wednesday morning as excessive runoff sent several feet of water rushing over city streets.

More urban flooding issues could arise in Los Angeles, San Diego, Palm Springs and Las Vegas.

Destructive mudslides and debris flows remain a serious concern, especially along the southern and western slopes of the mountains and in areas recently burned by wildfires.

Officials have reportedly ordered the evacuation of more than 230 homes in Los Angeles County.

Any motorist who considers crossing a flooded roadway should remember that it takes as little as 1 foot of rushing water to sweep a vehicle away. This includes pickup trucks and SUVs.

Even where flooding does not ensue, motorists should use caution. Water ponding on roads will heighten the risk of vehicles hydroplaning at highway speeds. Those planning to travel on interstates 5, 10, 15 and 40 are at risk.

A car moves through a flooded area of Los Angeles on Monday, Dec. 20, 2010. (AP Photo/Jae C. Hong) Upload your storm photos on the AccuWeather.com Facebook page.

Locally strong thunderstorms will pose an added danger to the Southwest. These thunderstorms could unleash even heavier bursts of rain, gusty winds, hail and an isolated tornado.

Due to the saturated ground, gusty winds could have an easier time bringing down trees.

An end to the relentless train of storms will finally come to California tonight as rain, thunderstorms and mountain snow become centered over Arizona and Utah. Flooding issues could arise in Phoenix.