Spring has arrived 20 days early in New York City - according to plants and trees

If you're looking at a calendar, you know that spring is just weeks away.

But if you're looking at the behavior of plants across a huge swath of the US - including Maryland, Virginia, and much of New York - spring is already here.

That's according to the National Phenology Network (NPN), a biological research organization that works with the US Geological Survey to track the cyclical behavior of plant life across the country.

NPN watches a number of "Extended Spring Indices," which use weather and plant behavioral data to track when the plants in a given region will start putting out leaves en masse - that is, when they will "start" spring.

This year has been marked by an unusually warm winter, which has led plants to begin spring rhythms very early. With each new leaf index map the NPN releases, the region of the country that's experiencing a premature spring has grown. On the most recent one, released, Monday, that region includes New York.

This GIF shows how the map has changed in recent weeks, as unseasonal plant behavior has moved north:

Of course, a warm February isn't necessarily followed by a warm March. Already, cold air and storms have made their way back into the forecast across much of the country. That could spell trouble for early-budding plants.

In Washington D.C., a weekend freeze followed the early bloom, "obliterating" the city's famous magnolia blossoms. Other plants that went into spring mode early may face similar dangers.