United States

By Brian Edwards, Meteorologist

September 02, 2012; 3:42 PM

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Photo courtesy of Photos.com.

A stormy August has led to above-normal rainfall and record amounts of thunder across the "Entertainment Capital of the World."

In a statement released by the National Weather Service in Las Vegas, the city recorded 13 thunderstorm days during the month of August.

A thunderstorm day is defined as the number of days that thunder is heard at the official observing station. That observing station is located at McCarran International Airport.

The 13 thunderstorm days during August broke the old record of 12 days which was set back in 1955.

The typical number of thunderstorm days during the entire month of August is only 3.3 according to the National Weather Service.

Looking at a little larger of a time frame, there have been 18 thunderstorm days this "monsoon season" which runs from July through September. According to the National Weather Service, "This currently ranks as the 7th highest total on record dating back to 1937."

Typically, Las Vegas only experiences 11.7 thunderstorm days per year.

Not only were the days in which thunderstorms occurred above normal, but that led to much higher precipitation than average.

McCarran International Airport received 2.28 inches of rainfall during the month of August which is a whopping 691% of normal! Normal precipitation for August is only 0.33 inches of rain.

The next question is why has it been so stormy across the Southwest?

In general, a large bubble of high pressure centered over the southern Plains and parts of the Four Corners has sent a generally persistent southeasterly flow of air into the Desert Southwest during the latter part of July and much of August.

This southeasterly flow is a very moist flow for the desert area as it transports tropical moisture from Mexico and the tropics into the Southwest.

With a constant flow of moisture, relative humidities remain high and strong August sunshine easily causes thunderstorms to form on a daily basis during the afternoon and evening hours.

A pattern such as this will ultimately lead to above normal rainfall and hence, the new record of thunderstorm days which was broken in Las Vegas.