Peak bloom, defined as when 70 percent of the cherry blossoms along the Tidal Basin are in bloom, should coincide with the beginning of this year’s National Cherry Blossom Festival, which spans March 20 to April 15.
Blossoms start to appear on trees several days before the peak bloom date and, weather permitting, can remain for a week or so. However, in some years, petals fall off sooner because of wind, rain or frost.
If peak bloom occurs on March 25, as predicted, it will be the third straight year on this date. Last year, the cherry trees were on the verge of a record-early peak bloom in early March, before a winter storm and hard freeze halted the blooming and damaged half the blossoms. They then reached an underwhelming peak late in the month.
From 2013 to 2015, peak bloom was later than normal, occurring on April 9 or 10, thanks to cold March weather.
Since records began in 1921, the average peak bloom date has advanced about five days earlier in the year as March temperatures have trended warmer. While the recent 30-year average date of peak bloom is March 31, the average peak bloom date from 1921 to 1950 was April 4.
The earliest peak bloom on record occurred March 15, 1990, while the latest was April 18, 1958.
There is no doubt the bloom cycle is off to a head start this year. For one, the trees went dormant in late December, when colder-than-average weather arrived. When they go dormant early, they also tend to wake up early. Last week’s record-setting temperatures above 80 degrees certainly helped them awaken.
The National Park Service announced Monday the cherry trees reached green bud stage on Sunday, Feb. 25. That ranks as the fifth earliest in the past 27 years. On average, the trees do not reach the green bud stage until the first week of March. In other words, the trees are already at least a week ahead in the bloom cycle.
Historically, the best predictor of peak bloom date is the average temperature in March. The model forecasts we have reviewed suggest March temperatures should be close to normal — although our confidence in such predictions is only moderate.
If we considered only the March temperature forecast to predict the cherry blossom peak bloom, we would call for a near average peak bloom date around March 31. But because the trees are ahead in the bloom cycle, we think they should come out about a week early.
Typically, it requires warm sunny days, above 70 degrees, and mild nights (well above freezing) to really accelerate the bloom cycle and result in a much-earlier than average bloom. Over the next two weeks, we do not see potential for such abnormally warm weather. The buds on trees should progress at a slow, steady pace.
We think there is potential (low confidence) for temperatures to spike to near 70 in the third week of March, which could help move the buds along toward peak bloom to begin the month’s final week.
Risks to the forecast
A lot of cloudy days in the 40s (or lower) and cold nights (in the 30s and colder) could push the peak bloom closer to the beginning of April. Alternatively, if temperatures predicted for the second week of March are not as cold and if we get into 70-degree weather the third week, the peak bloom might move up a little.
Below find our likelihood of different outcomes …
Peak bloom March 23-27: 50 percent chance (most likely)
Peak bloom March 18-22: 15 percent
Peak bloom March 28-April 1: 15 percent
Outside the March 18-April 1 window: 20 percent
How have our forecasts done historically?
This is the seventh year we have issued a cherry blossom peak bloom forecast. We have had reasonably good forecasts — hitting the peak bloom within our predicted window four times.
In 2016, we predicted a peak bloom date of March 26 (March 24-28 window), and it occurred March 25.
In 2015, we predicted a peak bloom date of April 11 (April 9-13 window), and it occurred April 10.
In 2014, we predicted a peak bloom date of April 9 (April 7-11 window), and it occurred April 10.
In 2013, we predicted an April 5 peak bloom date (April 3-7 period), and it occurred April 9.
In the very warm 2012, we predicted a peak bloom date of March 20, the same day it actually occurred.
More cherry blossom coverage
Capital Weather Gang’s Matt Rogers contributed to this post.