Snow Cover Extent Is Getting Weird In The Northern Hemisphere

The extent of snow and ice cover in the Northern Hemisphere during the
autumn has trended upward in the past 50 or so years, but.....
  

It's been a weird early winter for snow cover in Vermont and the rest of the North Country.

Where I live in St. Albans, tucked in the northwestern corner of Vermont, we have continuously had snow on the ground since November 13.

Which is really weird. The second half of November and early December usually have a thin snow cover off and on. Some days have no snow on the ground at all.

More often than not, you start to see a more consistent snow cover from mid-December on. Right now, the snow cover in my yard is the thinnest since November 16. And a warm, rainy storm forecast to hit Friday and Saturday will likely get rid of pretty much any snow that remains. Except for maybe a few drifts and snow banks.

This year's trend in northwestern Vermont is pretty much mirroring what is going on in North America as a whole, and has similarities to winter snow cover extent in the entire Northern Hemisphere.

North American snow cover extent this November was very likely the most widespread since at least 1966.  For the entire Northern Hemisphere, the snow extent in November was the third highest on record. These records go back 53 years.

But snow extent is really variable. Right now, in the grand scheme of things, latest maps from the Rutgers University Climate Lab show overall northern hemispheric snow extent to have settled into the near-normal category as of mid-December.

What's interesting from the Rutgers data is winter snow cover extent is all over the place during the winter. Some years, it's much greater than average, and in other years, it's much less.  There's no clear trend.

In the summertime, though, when snow and ice cover retreats to areas close to the North Pole, the extent of the snow and ice is consistently well below normal. 

........Spring snow and ice extent in the Northern Hemisphere has defintiely
fallen over the past five decades.  

Autumn snow and ice cover in the Northern Hemisphere has trended upward somewhat over the past 50 years and I've seen climate change deniers seize on that as helping "prove" their point that global warming is a hoax.

After all, if the world is warming, wouldn't there be less snow and ice extent?

Turns out, snow and ice extent isn't always the greatest measure of how the climate is changing.  Way back in 2014, the Washington Post Capital Weather Gang noticed the trend toward increased autumn snow cover in the Northern Hemisphere. They explained why this increased snow cover doesn't explain climate change:

"It simply needs to be near or below freezing for snow to fall. Temperatures that average 1-2 degres F above normal over the globe can still support snow in many places. Furthermore, slightly warmer than normal temperatures increase atmospheric moisture content, elevating potential snow amounts where they occur."

In other words, a storm that might have once been capable of producing three inches of snow in a given spot might now dump six inches of powder. It takes longer for six inches of snow to melt than it does for three inches, and that might be contributing to the increased snow cover in the North during the autumn.

It's possible, then, that climate change might, just might have something to do with the more widespread northern snow cover in the fall.

Interestingly, spring snow cover in the Northern Hemisphere is showing a noticeable decline over the past 50 years. That's important in terms of climate change.

The sun angle is higher in the spring than in the winter and fall. Snow cover tends to reflect much of the sun's heat back up to space. Bare ground absorbs heat, helping make overall temperatures higher.

Less extensive spring snow cover means more heat can be absorbed by the ground, thereby helping to heat air temperatures, creating a "positive feedback" for climate change.

Sunshine in the fall and winter does get reflected back to space on snow covered ground, too, and heat from sunshine gets absorbed by dark earth, but the effect is less pronounced because the low sun angle doesn't provide as much heat from the sun as you'd get in the spring.

Back here in Vermont, we know that snow cover locally can go up and down pretty quickly in the winter, with or without influences from climate change. Local, regional and national short term weather patterns dictate how much snow is in my back yard, and yours.

My yard in St. Albans, Vermont had more than a foot of snow cover on November 18 and a patchy inch or two now.

Who knows, within a couple weeks, I might be back up to a foot of snow on the ground, or more.  Winters here in Vermont always hold plenty of surprises.