It's never happened before.

The National Park Service has been keeping records for 96 years, and never before has the cold kept Washington's iconic cherry trees from bursting into full bloom.

This year could be the first time. Never before has the forecast been this cold for this long at this critical point for the blossoms.

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"This is sort of the perfect storm," said Park Service spokesman Mike Litterst. The blossoms right now are just about to burst into bloom and especially vulnerable to frost. "We've reached a critical stage, the fourth stage, peduncle elongation," said Litterst.

A week later, and we would have already seen their magic. A week earlier, and the delicate flowers would still be hiding in their woody buds.

"Because they don't have the protection of the closed up prior to the bloom," said Litterst, "these freezing temperatures, the possibility of snow coming, early next week, all of that can be critical."

The Park Service says 27 degrees is the deadly number. And lows are likely to flirt with that for the next week.

"Twenty seven degrees can see the loss of 10% of the blossoms," said Litterst. "That drops to 24 degrees, you could lose up to 90% of the blossoms."

Frost has already nipped our magnificent magnolias. The blooms are dying even as the forsythia weather the cold.

As the cherry blossoms go from green buds to florets to puffy white, they become more and more fragile.

It was cold last year too, but the timing was better.

On the bright side, the Tidal Basin may help. The water here can moderate the cold by a couple of degrees. And a couple of degrees may be all the blossoms here near the edge need to survive.

Two thirds of the cherry trees on the Mall are Yoshinos, and they're the ones in most danger. But the Kwanzan cherries bloom about two weeks later, and they should still be spectacular down towards Haines Point.