Snow Cover Building in Northern Hemisphere

Click for larger image.

Click for larger image.

Paul Yeager has already mentioned this on his blog (Cloudy and Cool), but I thought I would bring it to the attention of those who may not have check over there yet.

Paul mentioned the connection between Siberian snowfall and cold Northeast winters a couple months ago.  Now that snow cover is on the rise, we thought it was time to revisit the teleconnection and see what it may tell us about this upcoming winter.  Unfortunately, outside of the map you see above (you can get other maps, including 31-day animations, here), it’s tough to find much information about snow in Siberia.  If anyone else has any resources, please(!) let us know.

Something else of note is the snow cover in North America.  Using this site, you can go back to 1997 and view snow cover maps, like the one pictured above, for any day of the year.  It can provide some information about snow extent, but nothing about depth (which would be quite useful).  Still, skipping through previous years, it does appear North American snow cover is up this year when compared to recent mid-October maps.  So what might this tell us about the upcoming winter?

As snow cover and depth increases in Canada, the surface temperatures begin to cool (rapidly, in some cases).  Snow reflects somewhere between 75-95% of sunlight.  Since this light is reflected and not absorbed by the surface, it’s difficult for the air near the surface to warm during the day.  At night, the air cools rapidly as infrared energy radiates to space.  Repeat this process over the course of a week, two weeks, or a month and you can end up with a frigid airmass.  Now, if a ridge builds over Alaska or the West Coast, this air can be forced southward into the eastern 2/3 of the U.S. creating an intense cold wave.  We’ve already seen this pattern develop, but the air in Canada was nowhere near as cold as it will be in January.

So, if snow cover is above average in Canada, it stands to reason the opportunities for cold outbreaks in the U.S. will increase.  It still requires the correct jet stream pattern to force the cold air into the U.S., but at least there will be an arctic air mass to move.  Just another thing to keep an eye on as we move into the Winter months.  (Although, so far, it doesn’t appear Old Man Winter is going to wait for December to get going.)

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