Using data from NASA and the USDA, the U.S. Forest Service created a series of gorgeous maps that track that seasonal change around the U.S. using satellite data. The map below uses different colors to indicate the median start date of “greenup” for vegetation around the U.S. between 2000 and 2013. (Click on the map to enlarge it.)
The U.S. Forest Service doesn’t outright call this spring, since some parts of the U.S. do not experience the traditional four seasons. But "greening" does indicate the transition to a warmer and leafier time around the country.
While the South is generally warmer than the North, the map shows some interesting microclimates. For example, warmer temperatures arrive sooner at lower elevations, while higher elevations green later in the year. Differences within regions can also be based on the type of foliage or crops: Deciduous forests warm much more quickly than Midwestern croplands, for example, which is why the fields of Iowa and Illinois appear blue.
There are some exceptions to greenup: Some extreme deserts never get green, while evergreen forests are green year-round. As a result, central Pennsylvania, the Adirondacks, New England, and mountain areas of the Pacific Northwest may show greening that is actually just the melting of heavy snow in conifer forests.