Trees may be at least partially responsible for recent warmth


No doubt it’s been nice in the metro and much of the east over the last couple of days with temperatures well into the forties, and even in the 50s in La Crosse.  But there have been some BIG differences between temps east of I-35 and temps across the west.  While the metro has been basking in the mid-40s, temperatures in the west have been struggling to get above freezing.  While there are many things at play here, our vegetation maybe at least partially responsible.

First things first, the atmospheric components over the region the last couple of days have been conducive for warmer temps in the east and cooler temps in the west.  A stationary boundary that’s been splitting the area with light northwesterly flow in the west and light southeasterly flow in the east can mean the difference of a few degrees.  But the key here is that the winds were LIGHT.  Winds typically need to be fairly strong to overcome the really cold ground and snow cover this time of year.  There was also some fog on a couple of morning across the north and western areas, which can also hinder warming as it blocks much of the sun’s rays until it lifts late in the morning.  But nearly one of these alone can’t account for the drastic difference in temperatures across the area with mostly full sunshine.

The only other factor we can point to is vegetation.  So one of the images above shows the amount of snow on the ground… which is significant in many cases until you get down to La Crosse.  It’s this lack of snow cover in La Crosse that likely brought the city temps close to 60 degrees.  But with thick snow cover in the Twin Cities and much of northern Wisconsin, it’s these areas that you would expect to have cooler temperatures because deeper snow pack reflects more sunlight, the primary source of warming for the planet.  Well, that just wasn’t the case.  While the atmospheric conditions I mentioned earlier likely had some impact, it’s the abundance of trees and vegetation in these areas that likely allowed temperatures to soar.

An image above shows a high resolution visible satellite image of the Upper Midwest… basically what the Earth looks like from space if you were traveling around on the space shuttle.  Notice that areas in western and southern MN look far whiter than eastern and northern MN and much of Wisconsin.  This isn’t necessarily because of the amount of snow on the ground, but the lack of trees in the west and south because it’s mostly farmland.  It’s this “stark white” land that reflects far more solar radiation than areas with significant trees, because the trees aren’t white.  This lack of reflection allows for more radiation to be absorbed which manifests as heat and raises the temperature.

The combination of all of these factors has likely played in to the big temperature differences in the Upper Midwest through this week… and it will likely continue to round out the work week.

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