Blossoms and the Jefferson Memorial on Monday, April 13, 2015. (Jennifer Goonan via Flickr)

4:10 p.m. update: Due to the current and predicted warm temperatures, the National Park Service has moved up its peak bloom date forecast nearly two weeks from to March 31-Apr. 3 to March 18-23.

“Although the Park Service factored above average March temperatures into the original prediction date, potentially record-setting temperatures, averaging nearly 20 degrees above normal for the next week, have greatly accelerated the bloom watch,” the Park Service said in a press release.

So if you take Capital Weather Gang’s peak bloom forecast of March 24-28 (described in detail below) and the Park Service’s forecast of March 18-23 together, you get a predicted bloom window of March 18-28 – which could still be adjusted depending on weather specifics and how the buds respond.

Original post from 1:07 p.m.

Spring weather has burst into the D.C. area and the thoughts of Washingtonians are drifting away from snow flakes and toward cherry blossoms, primed to sprint through their bloom cycle this year.

This year’s feverish spring arrival favors a substantially earlier than normal cherry blossom peak bloom.  We are predicting the peak bloom to occur between March 24 and 28, centered around March 26. This is about five days ahead of the recent (30-year) average of April 1.

The peak bloom, defined as when 70 percent of the cherry blossoms along the Tidal Basin are in bloom should coincide with this year’s Cherry Blossom Festival running between March 20 and April 17.

Blossoms start to appear on trees several days before the peak bloom date and, weather permitting, can remain for a week or two. However, in some years, petals fall off sooner due to wind, rain, or frost.

March temperatures are frequently a key predictor for cherry blossom bloom dates; the warmer March is, the earlier buds typically burst.

Temperatures soaring into the 70s and even the 80s this week are stacking the deck for March to be among the top several warmest on record.

One week ago, the National Park Service predicted a peak bloom period of March 31 to April 3, but that was before the March outlook was so warm.  In the past, the Park Service has revised its predictions based on the weather conditions and the progress of the buds.

If the blossoms come early this year, it will be first such occasion since 2012, when they bloomed on March 20, tied for the third earliest date on record.

The last three years, the blossoms reached peak bloom on April 9 (2013) and April 10 (2014 and 2015), over a week late, following Marches that ranged from two to four degrees colder than normal.

Blossom peak bloom date records have been maintained by the National Park Service since 1921.  The earliest bloom date on record was March 15, 1990, and latest was April 18, 1958.

Since records began in 1921, the average peak bloom date has advanced about 5 days as March temperatures have warmed.

How did we come up with our forecast?

Our forecast for March temperatures to be at least five degrees warmer than normal represents the key reason we expect the blossoms to peak early.


National Weather Service 8-14 day temperature outlook.

Historically, when March temperatures have been this warm, peak bloom dates have ranged between about March 17 and March 26.


Graph shows relationship between March temperature difference from average and peak cherry blossom bloom dates in Washington, D.C.

We lean towards the later end of that March 17-26 window this year, because the cherry trees went dormant on late side this year.  The late dormancy was related to the record warm December.  The later trees go dormant, the later they tend to “wake up”. (More information on dormancy and bloom dates).

Some of the earliest blooms on record have occurred from the combination of a cold December and mild late winter, such that the trees “fell asleep” (went dormant) early but then woke up early. This year, we have only half of that combination, the mild late winter, since December was so warm.

Risks to the forecast

If the trees wake up quickly, peak bloom could occur even ahead of our forecast window given the mild temperatures forecast in the next couple of weeks. Warm sunny days and mild nights really accelerate the bloom process.

But if the trees are slow to awaken, the blossoms may not capitalize on the early warmth . Then, as temperatures later this month may not be as warm compared to normal, the possibility of cloudy days and/or cold nights could slow the bloom process down.

Taking this uncertainty into account, here’s our peak bloom forecast in probabilities:

Peak bloom March 24-28: 50 percent chance (most likely)
Peak bloom March 29-April 2: 15 percent
Peak bloom March 19-23: 15 percent
Outside the March 19-April 2 window: 20 percent

How have our forecasts done historically?

This is the fifth year we’ve issued a cherry blossom peak bloom forecast. We’ve had reasonably good forecast the previous four years – hitting the peak bloom within our forecast window three times.

In 2015, we predicted a peak bloom date of April 11 (April 9-13 window) and it occurred on April 10.

In 2014, we predicted a peak bloom date of April 9 (April 7-11 window) and it occurred on 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.

[Capital Weather Gang Cherry Blossom coverage]