(This story, first published Tuesday afternoon, was updated Wednesday morning with the addition of the National Park Service prediction.)
We predict a peak bloom about a month from now, between April 1 and 5, centered on the 3rd. This is a few days later than the recent (30-year) average of March 31, but matches the longer-term (1921-2018) average of April 3.
Last year, peak bloom occurred April 5, which is a bit on the late side. March turned out cold and snowy, which slowed the bloom process way down.
Our peak bloom forecast is similar to the National Park Service’s prediction of April 3 to 6, which was released Wednesday morning.
The Park Service had noted Tuesday that the blossoms reached the first stage in their bloom cycle as green buds emerged. The average date that green buds appear is March 5 — so this is right on time.
Peak bloom is reached when 70 percent of the cherry blossoms flower along the Tidal Basin. If our forecast verifies, peak bloom will correspond nicely with the National Cherry Blossom Festival, which runs March 20 to April 14.
Blossoms start to appear on trees several days before the peak bloom date and, weather-permitting, can remain for a week or so after. But in some years, petals have fallen off sooner because of wind, rain or frost.
Since records began in 1921, the average peak bloom date has advanced about five days earlier in the year as March temperatures have warmed. Although 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.
The Park Service cautions that “forecasting peak bloom is almost impossible more than 10 days in advance,” yet that hasn’t stopped them or the Capital Weather Gang from trying. For many years, it has issued peak bloom forecasts in early March and will release its prediction on Wednesday. The Capital Weather Gang has issued a peak bloom forecast since 2012.
Historically, average March temperatures are the leading predictor for peak bloom dates. When it’s warm, the blossoms tend to come out early, and when it’s cold, they come out late most of the time.
We’re expecting March temperatures to be near to slightly warmer than normal. This, by itself, might suggest a peak bloom date a little on the early side, in the last few days of March.
But it takes sunny, warm weather to really move the blossom buds along, and we’re expecting this month to be cloudy and wet. There’s no strong signal for an extended stretch of warm, sunny days any time soon, which would give the buds a boost. As such, we expect the overall progression toward peak bloom to be slow and steady, delaying the peak until the first week of April.
While it’s hard to predict the weather more than 10 to 14 days into the future, there’s some indication conditions might turn a bit warmer toward the tail end of March and early April, which might give the buds the final push they need to reach peak bloom.
Risks to the forecast
An excess of cold and cloudy days and freezing nights, more than we’re predicting, could push the peak bloom date into the second week of April.
But if we end up with more sunny, warm days and mild nights than we are expecting, then a late March bloom would become probable.
Given the uncertainty in how March weather will ultimately play out, we offer some alternative scenarios for the peak bloom date, in case our most possible forecast of April 1 to 5 doesn’t work out:
- Peak bloom March 27 to 31: 15 percent chance
- Peak bloom April 6 to 10: 15 percent
- Peak bloom outside the March 27-April 10 window: 20 percent
How have our forecasts done historically?
This is the eighth year we have issued a cherry blossom peak bloom forecast. We have had reasonably good forecasts — hitting the peak bloom within our predicted window in four of seven tries (although we’ve missed the past two years).
In 2018, we predicted a peak bloom date of March 25, and then revised it to April 1. Because of unseasonably cold weather and snow March 21 (the first day of spring), we had to revise our prediction one more time to April 10 on March 23. Actual peak bloom occurred on April 5.
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.