News release issued November 12, 2000, effective immediately.
For media inquiries, contact Caroline Booth Lara, Communications Specialist, (580) 224-6379.
  email: cblara@noble.org

Oklahoma Autumn Rainfall: How Much and Why?

ARDMORE – The burn bans, dry ponds and parched soils of summer and early autumn are becoming a fading memory to many Oklahomans, drowned by up to 20 inches of rain across much of the Sooner State during the last 60 days.

Taking the unofficial "prize" for the most rainfall (17.52 inches in the 60-day period ending November 12) is Idabel, located in the southeast corner of the state. Most of that total (approximately 12 inches) fell within the past two weeks.

Another famine to feast rainfall story focuses on the community of Grandfield, located southwest of Lawton in Tillman County. Grandfield picked up almost 16 inches of rain from October 1 through November 12 after suffering through less than a tenth of an inch in August and September combined.

Virtually the entire state received at least three inches of rain during the past 60 days. The lightest amounts were reported in the far northwest and a small area in the northeast part of the state.

The precipitation fell in a variety of ways, from all-day light rain and drizzle to torrential flood-producing cloudbursts. And the rain was as persistent as it was heavy; Ardmore, in south central Oklahoma, recorded measurable rainfall on an astonishing 22 of the 24 days ending Nov. 12.

The heaviest rains fell across parts of southwest, south central and central Oklahoma. According to data from Mesonet, Oklahoma's automated weather recording system, Ardmore, Chandler, Chickasha, Grandfield, Idabel, Norman and Walters all reported more than 15 inches of rain during the 60-day period. Numerous stations measured a foot of rain or more.

A foot of rain represents a considerable volume of water. That amount of rain falling over a one-square-mile area is the equivalent of approximately 208 million gallons. Depending upon terrain, soil type, previous weather conditions, and rainfall intensity, the majority of the water can either soak into the soil or run off. Rainfall that soaks into the soil is usually regarded as beneficial. Runoff can be good or bad – good for filling stock ponds depleted by heat and drought, but bad when runoff is excessive and results in flash flooding, displaced residents and washed-out roadways.

Heavy autumn rains in Oklahoma are often the result of hurricanes from the Gulf of Mexico hitting the Texas coast and curving northward, or similar systems in the Pacific making landfall in Mexico and spreading moisture northeastward into the southern Great Plains. But this year it's a persistent jet stream that's the conveyor, allowing moisture from both the Gulf and the Pacific to flow freely into Oklahoma. The triggers are upper-level disturbances moving across the state and frontal systems that stall across Oklahoma and Texas.

The combination of these factors has shattered the normal rainfall patterns this fall. Parts of Oklahoma – including areas in the Panhandle, northwest, southwest, south central and central portions of the state – have received more than five times the normal rainfall during the past 30 days. The majority of the state was two to three times as wet as normal during that period.

Note: Information for this article was obtained from the Oklahoma Mesonet, operated by the Oklahoma Climatological Survey, and the Arkansas-Red Basin River Forecast Center in Tulsa, Oklahoma.

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Main Story: Rain Brings Relief for Oklahoma Agriculture
Downloadable map of OK rainfall gif (84k gif)
Downloadable map of OK Tiff (3.1 Mb)

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The Samuel Roberts Noble Foundation, headquartered in Ardmore, Okla., is a non-profit organization conducting agricultural, forage biotechnological, and plant biology research; providing grants to numerous non-profit charitable, educational and health organizations; and assisting farmers and ranchers through educational and consultative agricultural programs.

To learn more, check out the Noble Foundation Web site at http://www.noble.org.

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