Spring’s early arrival in Washington could have severe consequences for its famed cherry blossoms at the Tidal Basin. A punishing, long-duration cold snap arriving this weekend could cause irreparable damage to the blossoms, which have advanced to a vulnerable stage.

On Wednesday, the National Park Service declared that the blossom buds had reached the peduncle elongation stage. This means at least 70 percent of the buds have flowers on the brink of bursting out. Often, peak bloom occurs within a week of this stage. At earlier stages, the buds are encased and more protected from the cold. Now, they are tender and exposed.

The Park Service’s Michael Stachowicz said some buds have even reached the puffy white stage, in which flowers are starting to emerge. Thursday afternoon’s high temperatures above 70 degrees will only push the buds further along in the bloom cycle.

But on Friday, an Arctic cold front will plunge into the metro region, bringing the coldest weather since January over the weekend and into next week. The National Weather Service predicts temperatures in the low-to-mid-20s Saturday, Sunday and Monday mornings.

Stachowicz said that once the temperature drops below 27 or 28 degrees for a half-hour, damage to about 10 percent of the blossoms can occur.  “If you get one day of 10 percent kill, I wouldn’t be too concerned,” he said. “But three days in a row could start to be pretty damaging.”

He added that if temperatures drop to 24 or 25 over three days, “you start to get into the 90 percent kill range,” which is what the Weather Service is forecasting.

Since the Tidal Basin is adjacent to water, which has a moderating influence on temperatures, it may not be as cold there. But some damage seems inevitable, Stachowicz said.

“I think we’re going to get some damage,” he said. “I don’t want to be alarmist about it, but we’ve been brought along to a tender stage.”

Stachowicz made clear that while cold weather could damage the buds, they won’t damage the cherry trees themselves. He is optimistic that some of the buds that are not as far along in the bloom process will survive the blast of cold. “We have various stages, so we have various sensitivity to the weather,” he said. “Our hope is that there’s enough variation in our bud stages that we could still put on a pretty good show.”

The cold weather forecast over the next week prompted the Park Service to push back its forecast for peak bloom from March 14-17 to March 19-22 on Wednesday. Normal peak bloom (using data from 1981 to 2010) is around April 1. The earliest peak bloom on record occurred March 15, 1990.

Capital Weather Gang’s peak-bloom forecast is March 15 to 19. We are not updating this prediction but favor the peak bloom to occur toward the end of this window.

Once the cold snap ends, assuming some of the blossoms survive, it won’t take much to push them to peak bloom. “If we make it through this cold snap unscathed, you could get to full bloom with one 70-degree day,” Stachowicz said.

The long-range forecast is for a steady warming trend after Thursday, March 16 — with afternoon high temperatures rising through the 50s. But it’s hard to say, at that point, how many blossoms will be left to see.

The worst-case scenario, which is plausible according to forecasters, is that a snowstorm occurs Monday night and Tuesday, behind which even colder air pours into the D.C. area during the middle part of next week.

Fresh snow cover would promote frigid overnight lows that could drop into the teens. NOAA’s Global Forecast System model, which predicts accumulating snow Monday night and Tuesday, predicts widespread lows in the teens Thursday.

Temperatures that cold would kill off not only the more vulnerable flowering buds emerging now but also those in earlier stages, which are “the bench or backup players,” according to Stachowicz.

Should the blossoms fall victim to this March cold snap, it will reveal the devastating consequences of what scientists call “false spring.”

It was the warmest February on record in Washington, and temperatures were warmer than they are in a typical March. Spring arrived three weeks early in the region, according to the U.S.A. National Phenology Network, which tracks the timing of the season through the monitoring of leafing plants and flowering blossoms.

Spring’s early arrival left the region’s vegetation vulnerable to freezing March temperatures. Temperatures in the 20s last weekend, before the cherry-blossom buds were vulnerable, led to “a pretty severe magnolia kill,” Stachowicz said.

Such false springs have a history of unwelcome effects on flora. In March 2012, a false spring in the upper Midwest, the earliest on record, was followed by a freeze that left behind half a billion dollars of agricultural damage in Michigan. The federal government declared the state a disaster area.