Late-season chill prompts change in peak bloom dates of DC's cherry blossoms

By Ashley Williams, AccuWeather staff writer
March 23, 2018, 2:42:43 PM EDT

Unseasonably cold conditions and heavy snow in parts of the northeastern United States over the past few weeks have led the National Park Service to push back the peak bloom dates for Washington, D.C.’s popular cherry blossoms.

The peak bloom period was initially projected to fall between March 17 and 20, as was announced on March 1. The National Park Service defines the peak bloom date as the point at which 70 percent of the Yoshino cherry blossoms are open.

The original dates would’ve coincided perfectly with the start of D.C.’s annual National Cherry Blossom Festival, one of the country’s most anticipated spring festivals. The 2018 festival takes place from March 17-April 15.

On March 12, officials with the National Mall and Memorial Parks revealed via social media that the window was updated to March 27-31.

However, likely to the dismay of festivalgoers centering their travel plans around the peak bloom dates, officials announced that the window has been pushed back even further to April 8-12.

The National Park Service recalculated the new peak bloom dates using recent temperature data and by monitoring the current progression of the blooming phases as well as the weather forecast in the coming days, officials wrote in a Facebook post.

“The forecasts are usually pretty good, but it can be hard to tell exactly when peak bloom will be,” said Just Energy climate and sustainability specialist Michelle Pettit.

The peak bloom date adjustment isn’t uncommon. Predictions have been known to change several times before peak bloom finally comes into full effect, Pettit said.

“The new prediction is actually more in line with peak bloom dates for the past several years, so it's reassuring to see that they haven't changed to be drastically earlier than in the past,” Pettit added.

According to the National Park Service, the most likely time to reach peak bloom occurs during the period between the final week of March and the first week of April.

D.C. cherry blossoms - AP Photo

Cherry trees around the Tidal Basin frame the Martin Luther King Jr., Memorial at daybreak as Washington, D.C., continues to watch and wait on Monday, March 12, 2018, for the famous trees to bloom. (AP Photo/J. David Ake)

Most trees and plants enter dormancy as a defense mechanism during the shorter, colder days of fall and early winter and, like most biological processes, dormancy is driven by chemistry, said AccuWeather Senior Meteorologist Jason Nicholls.

“As a general rule, chemical reactions such as budding and blooming of trees move along at a faster pace when it’s warmer,” Nicholls said. Warmer weather allows the buds to swell.

Experts say that the amount of chemical reaction that occurs within a plant, for example, will double for every 18 degrees Fahrenheit (10 degrees Celsius) of temperature increase because particles interact more frequently.

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Four nor’easters recently barreled through the Northeast with powerful winds and significant snowfall.

“Cold weather in early spring keeps this process slow or makes the plant stay dormant longer,” Nicholls added.

It has been reported that overall, this year’s late-season storms haven’t caused much harm to budding plants.

“The main reason there probably hasn't been a lot of damage to budding trees so far this year is that there hasn’t been a long enough period of warmth to break many trees out of dormancy,” Nicholls said.

In 2012, a greater number of trees and plants were damaged due to prolonged warmth in March, which sped up the budding process and resulted in an early end to the dormancy period, according to Nicholls.

“As a result, the cold weather in early April 2012 led to damage because the plants were more susceptible to the cold,” he said.

A benefit of the cold weather is that the blooming process will slow down, possibly resulting in a longer blooming period. Cherry trees are known for their fleeting blooming periods, which can last about four or five days and possibly up to two weeks, depending on weather conditions.

While cold weather may delay the blooming period, low temperatures pose yet another threat to the cherry blossoms. A cold snap occurring after warm weather has already triggered the opening of the blossoms could damage and kill them, as seen during 2017’s cherry blossom season.

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