Things have warmed up since 1990, when the U.S. Department of Agriculture came up with its plant hardiness zone map--the reference gardeners use when figuring out what kinds of plants will thrive in their yards. The Daily Climate has a story about the departments revisions to the map. A new version -- with all those colored ribbons moved a little farther north, should appear later this year. The Arbor Day Foundation published its own revised map in 2006, along with this nifty animation showing how the zones have changed.
The USDA's 1990 map of the region's plant hardiness zones.