The Washington Monument is pictured behind a cherry blossom tree in Washington, March 24, 2011. REUTERS/Hyungwon Kang

No worries for D.C. Cherry Blossom festival Images: Washington D.C. Cherry Blossom festival

Washington's National Cherry Blossom Festival, one of the biggest U.S. springtime parties, is expected to see an earlier-than-normal peak bloom between March 24 and 31, a National Park Service forecaster said on Thursday.

The prediction carries special weight since this year's celebration marks the 100th anniversary of Japan's gift of cherry trees as a sign of friendship with the United States.

A more exact forecast will come in 10 days or so as the March 20-April 27 festival's start nears, Rob DeFeo, the Park Service's regional chief horticulturalist, told reporters.

"Unless we have an Ice Age, we're not going to see a late bloom," he said after a news conference on the peak bloom date.

The Cherry Blossom Festival draws more than a million visitors to Washington to enjoy the white and pink blooms on 3,770 trees around the capital's Tidal Basin. It pumps more than $100 million into the District of Columbia's economy.

DeFeo said the March 24-31 range was the first time he had predicted peak bloom entirely in March. He said he had accurately forecast the peak 16 times in 20 years.

April 4 is the average date for the cherry trees to reach their peak, or when 70 percent of the blossoms of the Yoshino cherry tree variety are open. The bloom normally lasts about 17 days.

About 100 of the original 3,000 trees donated to the United States in 1912 are still alive, even though the normal life span is 50 years, DeFeo said.

Like much of the United States, Washington has seen an unusually mild winter, leading to fears the cherry trees might bloom too early and spoil the celebration.

Temperatures were forecast to reach almost 70 degrees on Thursday. The balmy weather prompted some strollers on downtown streets to put on shorts and T-shirts.

The 2012 Cherry Blossom festival includes art shows, concerts, kabuki theater, kite flying, fireworks, light shows, a parade, bicycle tours and a rugby tournament.