Arizona Monsoon
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A monsoon comes yearly to the Highlands and deserts of not only India, but Arizona, too. I'm Dave Thurlow and this is The Weather Notebook. You don't have to leave the U.S. to get a taste of monsoonal drama. The southwest part of our country gets its own, modified monsoon every summer.

The forces at work in an Indian and an a North American monsoon are similar: a buildup of summertime heat followed by an influx of warm, moist marine air from the south. But there are some important differences between the classical Indian monsoon and the American version. For one thing, the rains aren't as constant or reliably heavy in Arizona and New Mexico as they are in India. The huge, east-west wall of the Himalayas helps to force moist air upward and intensify Asian rains. During the two peak monsoon months here, June and July, Tucson, Arizona gets about 4 and a half inches of rain, but New Delhi, India, gets socked with more than 15 inches, over half of it's annual

total. Even so, localized storms can dump several inches in an hour or two across the Southwest U.S. Moisture can reach the Southwest from two nearby bodies of water, the Gulf of Mexico and the Pacific Ocean. When an upper-level storm enters the picture; the two wet weather sources often team up.

Although, Asians delight in the monsoon as a life-giving force, the residents in Phoenix aren't always so happy. Daytime highs might drop from 110 to around 90 degrees Fahrenheit, but relative humidities can rise from the single digits to 40 or 50 percent. There is a silver lining: along with welcome rainfall, monsoonal storms give folks in the Southwest some of the most spectacular cloud and lightning shows on earth. The Weather Notebook is produced by the Mount Washington Observatory,funded by The National Science Foundation, and underwritten by Subaru -- the beauty of All-Wheel Drive.