Robert DeFeo pondered the recent weather and the forecast for the next few weeks. He had breakfast with the tree crews, which changed his mind a little. He examined other trees and plants around the Mall.

And on Thursday morning he stood up in his blue denim shirt and cherry blossom tie and announced that Washington’s Centennial Cherry Blossom Bloom would begin early, around March 22, and peak between March 24 and 31.

Then he was mobbed by the news media.

It was perhaps the most momentous blossom forecast in a hundred years, and the biggest of the National Park Service cherry tree expert’s 21 years of blossom prognosticating, he said.

His anouncement at the Newseum marked the unofficial start of this year’s celebration of the 100th anniversary of the planting of the much-pampered trees on the Tidal Basin on March 27, 1912.

The National Cherry Blossom Festival’s birthday bash — expanded from about two weeks to almost six this year — doesn’t begin until March 20 and runs until April 27. But some events are starting as early as next week.

Also starting early has been the warm weather — which can accelerate the bloom. In February, the temperature were freezing on only four days, and it reached 50 or above on at least 16 days. It hit 72 on Feb. 1.

According to the Capital Weather Gang, this February was the fourth warmest on record. The average monthly temperature of 44.3 degrees was 5.3 degrees above average.

Thursday’s high was 70, with sun and a mild breeze.

But DeFeo said in an interview Tuesday that the earlier warm weather is moot.

“It really only matters as to what happens from now on. . . . Now is the time where, if it gets really, really warm, things could accelerate,” he said.

According to the Capital Weather Gang, temperatures over the next week or so could be generally above normal, although the forecast is for cooler conditions next week.

An early start to the bloom could mean an early end and could leave the closing weeks of the extended blossom festival with no cherry blossoms. Festival officials said, however, that this year’s celebration goes “beyond the blossoms.”

D.C. Mayor Vincent C. Gray (D), who spoke at Thursday’s event, said the festival draws more than 1 million visitors a year and generated $126 million last year for the local economy. He said he hoped for $200 million this year.

The blooming period is usually about two weeks, more or less.

The average peak bloom date is April 4, but the capricious blossoms have peaked as early as March 15, in 1990, and as late as April 18, in 1958, according to DeFeo’s records.

The festival is marking the centennial of the first planting of cherry trees on the basin, by first lady Helen Taft. The initial 3,020 trees were a gift of friendship from Tokyo to Washington.

Within a decade, tens of thousands of visitors were flocking to the Tidal Basin to see the trees. And since then, the blossoms have become one of the city’s premier tourist attractions and an international hallmark of Washington.

This year, first lady Michelle Obama is serving as honorary chairman of the festival, which will be augmented by the new Martin Luther King Jr. Memorial in the middle of the Tidal Basin blossom belt.