A sure sign of actual spring: When the plants and trees and other vegetation returns to the lush green color we spend all winter wishing for.
But when does that "greenup" come? Some data from the ForWarn service (a collaboration headed by the USDA Forest Service) gives us a pretty good window.
First, let's start with the overall. Here's a look at the median greenup date based on recent years, for the entire country. It's color-coded, as you'll see on the map. (Click to enlarge.)
Minnesota varies, anywhere from mid-March in the northeast, all the way to June in the opposite corner of the state.
The Washington Post listed a few reasons: One, some vegetation (deciduous forests for example) green faster than other types (such as Midwestern cropland). Elevation also plays a role.
As does being in an urban or rural area. The Post says the amount of buildings and asphalt concentrated in cities cause those areas to generate more heat, leading to a faster greenup than in rural areas.
Here's a very close-up look of the Twin Cities area.
Says ForWarn of the data: "Minnesota lies farther north than the other cities in the Midwest described above, so it is no surprise that later-season orange and reds replace the March-April greens of the urban landscape. Subtle structures within this urban area reflect differences in density of vegetation and impervious surfaces."
What can you take from this, besides knowing when it might get green?
Well, whether you're a forest manager, a farmer with crops, or even someone with a carefully tended garden in the backyard, you're able to look at what you're seeing – and compare it to what you should be seeing based on 14 years of data, Bill Hargrove, a research ecologist with the Forest Service, told BringMeTheNews
A deeper look
Let's take a more detailed look at Minnesota as a whole, divided into two categories: natural vegetation, and crops.
First, natural vegetation, which includes exactly what you'd think – trees, flowers, bushes, etc. etc.
Here's ForWarn's mean greenup date data for the U.S. If you look closely at Minnesota (click to enlarge), which ranges anywhere from mid-March to May.
And then here's ForWarn's agricultural map data, which looks at greenup dates for crops and farm land. Those typically come later in the spring than the natural vegetation, with the earliest often coming in April.
One thing you might notice – the agricultural and natural maps don't overlap. Which seems odd, since these areas mostly have both croplands and nature intermixed.
Hargrove says it's all based on data and pixels. Basically, they have to break each section up into either natural or agricultural, because the map can only get so detailed. So they do a more thorough look, then look at which type of vegetation is the majority in each little section.
So every pixel on those maps is 13 acres.
You can actually see detailed land-type maps on the ForWarn site. It tracks the land across all 48 contiguous U.S. states.