The Washington Post

Look toward late March for peak cherry bloom


Early blooms are emerging across Washington because of a historical­ly mild January and February. One might think the famed Yoshino cherry blossoms at the Tidal Basin would soon follow — but an abrupt change in the weather pattern by the second week of March may well put their bloom cycle on hold.

Because of the prospect of a chilly March in the D.C. area — slowing the start of spring — we’re anticipati­ng peak bloom will take place between March 25 and 29. That’s just a few days earlier than normal.

The cooler weather and more gradual progressio­n into spring is good news for the blossoms. If it remained abnormally warm through the first half of March, the buds could open prematurel­y, leaving them vulnerable to freezing temperatur­es that are not uncommon in the middle of the month. This happened in 2017 when the buds advanced to the fifth stage of six and were badly damaged by snow and temperatur­es that plunged into the 20s.

Because of our warming climate, the cherry trees are flowering earlier than they used to, potentiall­y making them more vulnerable during late freezes. Bloom data dates to 1921 and the average peak has advanced about five days, from April 4 to March 31. The earliest peak bloom on record occurred on March 15, 1990, while April 18, 1958, marks the latest peak. Last year, peak bloom occurred on March 21.

Peak bloom is declared by the National Park Service when 70 percent of the cherry blossoms flower around the Tidal Basin, which is near the National Mall. Once peak bloom occurs, the blossoms can remain on cherry trees for another week or so if it’s warm and winds are light. Abnormally cold, rainy or windy weather can strip the trees of petals within a few days.

Our predicted peak bloom window coincides with the National Cherry Blossom Festival that runs from March 20 to April 16. The Park Service is set to make its peak bloom forecast on Wednesday.

Forecast rationale

March temperatur­es are the biggest driver of our forecast for the peak bloom date, as they have historical­ly been the best indicator. When it’s warmer than average in March, the blossoms tend to peak in mid- to late March; when it’s on the chilly side, they tend to flower between late March and mid-april. This March, we are projecting temperatur­es slightly cooler than normal.

February temperatur­es influence the bloom date to a lesser degree. But there is a weak correlatio­n between warm Februaries, like we’ve seen this year, and early peak blooms.

Aided by this year’s warm February temperatur­es, the blossom buds reached their first stage — green buds — on Feb. 23 — which is the second earliest date in the past two decades. We imagine they’ll advance to their next stage — when florets are visible — in the next several days as it remains milder than normal. It’s possible that by next week, when more mild weather is expected, they’ll reach the third stage — the extension of florets.

But as we look toward the middle of March, there is the potential for a very chilly period, which could halt the buds’ progressio­n. They may not reach their final three stages until the second half of the month. (The buds typically aren’t vulnerable to freezing temperatur­es until they reach the fourth or fifth stage.)

We analyzed past years that featured a very warm February and then a somewhat cool March, like we expect this year, and peak bloom dates were usually toward the end of March in those cases.

How the forecast could go wrong

Our projected peak bloom window of March 25 to 29 is based on the idea that temperatur­es will warm up after the mid-march cold stretch. If they don’t, the peak bloom date could slip into early April.

The buds tend to accelerate through their stages when days are sunny and warm — in the 70s and 80s — and nights are mild. But, at least through the first half of March, we see limited potential for such warmth. This Thursday, when highs could approach 70, will probably be the warmest day in the next several weeks.

As such, we think if our peak bloom window is off the mark, it will probably occur later rather than earlier.

Here are the odds of alternativ­e peak bloom windows:

Peak bloom before March 21: 10 percent

Peak bloom March 21 to 24: 10 percent

Peak bloom March 30 to April 2: 10 percent

Peak bloom April 3 to 7: 10 percent

Peak boom after April 7: 10 percent

How have our forecasts done historical­ly?

We have issued cherry blossom forecasts since 2012 and have hit the peak bloom within our predicted window in five of 11 tries. Last year, we predicted a peak bloom between March 22 and 26; it occurred one day before that window.

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 ?? MATT MCCLAIN/THE WASHINGTON POST ?? A pedestrian passes one of the blooming cherry trees at the Tidal Basin last year. The blossoms are a big tourist draw for the District.
MATT MCCLAIN/THE WASHINGTON POST A pedestrian passes one of the blooming cherry trees at the Tidal Basin last year. The blossoms are a big tourist draw for the District.

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