Fall snow cover in Northern Hemisphere was most extensive on record, even with temperatures at high mark

November snow cover extent in the Northern Hemisphere (Rutgers Global Snow Lab)

In 46 years of records, more snow covered the Northern Hemisphere this fall than any other time. It is a very surprising result, especially when you consider temperatures have tracked warmest on record over the same period.

Data from Rutgers University Global Snow Lab show the fall Northern Hemisphere snow cover extent exceeded 22 million square kilometers, exceeding the previous greatest fall extent recorded in 1976.

New Jersey state climatologist David Robinson, who runs the snow lab, shared these additional snow cover statistics:

• For the fall (September, October, and November), when Northern Hemisphere snow cover set a record:
  • North America had its most extensive snow cover on record
  • Eurasia had its third most extensive snow cover on record
• In November:
  • North America had its most extensive snow cover on record
  • The Lower 48 had its most extensive snow cover on record (which is not surprising given the Arctic blast and snow events in the final two weeks)
  • Canada had its second most extensive snow cover on record

The sprawling snows may seem counter-intuitive considering recent reports that September and October were the warmest months on record for the globe according to NOAA (and November the second warmest on record, according to satellite analysis from the University of Alabama-Huntsville).

However, the amount of snow does not necessarily correlate with temperature.  It simply needs to be near or below freezing for snow to fall.  Temperatures that average 1-2 degrees 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.

A recent modeling study showed high latitude extreme snows could increase 10 percent by the end of the century under global warming scenarios.

Related: Extreme snowfall events will continue even in global warming, says study

Rather than temperature, the more important factor for snow cover is the jet stream circulation.  If and when the jet stream is able to transport cold air from the Arctic into the mid-latitudes, that opens the door for snow cover to build south.  This fall, the jet stream took some notable southward excursions, spreading snow into places where it’s not always common.

The reasons for the unusual jet stream behavior are an active area of scientific research and discussed some in these two posts:

1) Snowed under and frozen over: U.S. weather is off the rails, but why?

2) There’s growing evidence that global warming is driving crazy winters

In a previous version of this story, we said there were 49 years of snow records for the Northern Hemisphere, but it is actually 46 years.