Sunrise at the Tidal Basin with the cherry blossoms at peak bloom on April 9, 2013. (Kevin Ambrose)

Following a springlike winter, leaves are emerging and flower buds are bursting in the Washington region up to three weeks ahead of schedule. Soon, too, the famed cherry blossoms at the Tidal Basin will awaken, and possibly on the early side as well.

We are forecasting peak bloom between March 25 and March 29, centered on the 27th. This is a few days earlier than the 30-year average of March 31, and a week before the longer-term (1921 to 2019) average of April 3.

Last year, when temperatures weren’t as mild, peak bloom for the cherry trees was declared on April 1.

Given how mild it has been and how quickly other flowers are blooming around the region, it might seem surprising that we do not expect the cherry blossoms to peak even sooner. However, the weather predicted over the next couple of weeks does not seem like it will be warm enough for them to emerge much earlier than late March.

Peak bloom is reached when 70 percent of the cherry blossoms flower along the Tidal Basin. If our forecast holds, peak bloom will coincide with the National Cherry Blossom Festival, set for March 20 to April 12.

Blossoms start to appear on trees several days before the peak bloom date and, if it’s warm and dry and winds are light, 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 spring, as March temperatures have warmed. Although the most 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 was logged March 15, 1990, while the latest was April 18, 1958.

The National Park Service cautions that “forecasting peak bloom is almost impossible more than 10 days in advance,” yet that hasn’t stopped it from trying. For many years, it has issued peak bloom forecasts in early March.

Update: On Wednesday, a day after we issued the above forecast, the Park Service predicted peak bloom during the March 27 to 30 window, very similar to our forecast.

Forecast rationale

Peak bloom dates and temperature difference from normal during March.

Historically, average March temperatures are the leading predictor of peak bloom dates. When it’s warm, the blossoms tend to come out early, and when it’s cold, they generally emerge late.

Last year, March temperatures were close to average; so was the cherry blossom peak bloom date (April 1).

This year, we’re expecting March temperatures to be several degrees warmer than normal, favoring an earlier bloom. The blossoms are off to a head start, due to the mild temperatures in February, and have reached their initial “green bud” stage about five days ahead of average.

However, we’re not expecting a historically early bloom. Unusually warm, sunny days and mild nights tend to push the blossoms toward peak bloom fastest, and although we’re predicting above-average March temperatures, we don’t see exceptionally warm weather in the forecast.

In the years with the earliest peak blooms, such as 1990 and 2012 (March 20), early to mid-March featured multiple sunny days with temperatures in the 70s and 80s. This year, we expect our milder days to be in the 50s and 60s instead, favoring a steady progress toward peak bloom, rather than a sudden bud burst.

15-day high and low temperature forecast from the European modeling system. (WeatherBell)

How the forecast could go wrong

An excess of cold and cloudy days and freezing nights — more than we’re predicting — could push the peak bloom date into April. But if we end up with more sunny, warm days and mild nights than we are expecting, then an unusually early March bloom would become probable, before March 25.

Given the uncertainty in how March weather will play out, we offer some alternative scenarios for the peak bloom date, in case our most possible forecast of March 25 to March 29 doesn’t work out:

  • Peak bloom before March 20: 10 percent chance
  • Peak bloom March 20 to 24: 15 percent chance
  • Peak bloom March 30 to April 3: 15 percent chance
  • Peak bloom after April 3: 10 percent chance

This peak-bloom outlook is made on the basis of available weather forecast data in early March and may require revision if big shifts in the forecast occur.

How have our forecasts done historically?

We have issued cherry blossoms forecasts since 2012 and have a solid track record — hitting the peak bloom within our predicted window in 5 of 8 five tries.