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    Flash Flooding Breaking Out Around Las Vegas

    By By Brian Edwards, Meteorologist
    September 17, 2011, 1:27:54 AM EDT

    Drenching thunderstorms will plague the desert Southwest through tonight and beyond, bringing a flash flood threat to cities such as Las Vegas, Needles and Palm Springs.

    A storm in the upper atmosphere continues to spin off the coast of Southern California, sending moisture into the Desert Southwest.

    Flash flooding occurred in many places Monday and Monday night across Arizona as well as southern California and Nevada.

    Topock, Ariz., received over an inch of rain in less than 45 minutes while lightning sparked a fire at a house near Kingman, Ariz.

    A water rescue had to be performed 4 miles from downtown Las Vegas, Nev. this morning. Water was flowing across several roadways and several closures were reported.

    Similar events could occur this afternoon and tonight across the same general region as widespread showers and thunderstorms develop with some heating.

    Thunderstorms will be slow-moving and could produce rainfall rates of 1-2 inches per hour.

    Enough cool air lies aloft that hail to the size of dimes could again fall in the strongest storms.

    These storms have the potential to cause flash flooding and not only over the area being directly hit. Runoff from rain upstream can rapidly flow into washes, canyons and arroyos miles away. Use extreme caution when hiking in these low-lying areas this week.

    300x200_09131600_sw flood

    Lightning strikes associated with the thunderstorms will also bring not only a risk to hikers, but also the potential for igniting wildfires, where little rain falls. Spring growth has been drying all summer long in the region.

    Another phenomenon that residents could face the next few days is a dust storm. Blowing dust was reported Monday night in Phoenix and Yuma as thunderstorms were nearby.

    Dust storms often occur with strong outflow from thunderstorms. The strong outflow is produced when a thunderstorm downburst, which occurs when the core of a thunderstorm collapses, suddenly forces air and water toward the ground. The fast-moving air has nowhere to go, but spread out in all directions.

    People vacationing or living in the cities of Palm Springs, Twentynine Palms, Las Vegas and Cedar City should keep an eye to the sky through tonight. If threatening weather approaches the area, take shelter immediately in the nearest sturdy building.


    Motorists should be prepared for suddenly reduced visibility in blowing dust or torrential downpours over the next several days. At times, the visibility could fall below a quarter of a mile.

    Flash flood watches are already in effect for much of the desert Southwest after the rain that fell on Monday.

    The threat won't just end beyond tonight either. The aforementioned upper-air storm will translate eastward very slowly the next few days, becoming centered near Las Vegas, Nev., by Wednesday night.

    This will lead to additional bouts of drenching showers and thunderstorms for the same locations through the end of the week.

    Drier air will finally move into this region by Thursday and Friday as this storm moves to the east.

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