Monday, May 12, 2014

Winter 2013-14 was Cold but not that cold. But still it was Cold.

Did the winter of 2013-14 break you?  Was it the bad trip you were convinced you couldn't escape?

Or, did it make you think, “Finally!  Where have these winters been?”

Whichever it was for you, I'd love to know.

The winter got a lot of attention, and the media pounced, with the usual sensationalistic flair that keeps people tuned in and/or reading.  Atmospheric scientists, almost as a kneejerk, went on the defensive, trying to convey the difficult-to-convey: yes it’s cold, yes it hasn’t been this cold in a long time, but no this is not the worst ever—not even close, and by the way, we’re wussies for thinking it is.

But if you remove the sensationalism, remove the curmudgeonism that often holds hands with myth-busting, there really was something to this winter.  So how do we talk about it?

Look, whether you loved it or hated it, if you lived in the central, southern, eastern, northeastern, or northern US (I just named a big
chunk of the country), this was a long, cold, persistent and in many cases, a snowy season.  Only the southwestern and far-southeastern US escaped it.   

These colorful maps from NOAA show that during “meteorological winter,” December through February, daily high (image above) and low temperatures (image below) averaged several degrees below normal, or colder, over the central and northern US.

Of course, over those same parts of the country, “real” or “experiential” winter lasts more than three months; really, you can think of winter as that November-through-March period, when legitimately-cold, snowy or icy weather is on the table.

So above, here is a differently-colorful map, showing the departure from normal temperatures from November 1 through March 31.  Please focus on the Upper-Mississippi Valley/Western Great Lakes area.  This map is telling you that if you take the average of the high and low every day, and then take the average of those averages, for the full five-month period, you were coming up 6, 7, 8, even 9 degrees (F) colder than normal.  That is significant.  It's not easy to run 9 degrees below average for two weeks, let alone five months!

Now here is where it gets fun.  Averages are based off of 30-year "normals" that are calculated every ten years, with the most recent being the 1981-2010 period.  So this winter was 6,7,8,9 degrees colder than the most recent normals.  But we also know that for most of the US, the most recent normals are the warmest on record. And the period ending in 2000 had the second warmest normals on record. This is not news: you should have gotten the memo that things have been getting warmer.

But it makes contextualizing the winter difficult.  A winter that's 6-9 degrees colder than "normal" means something different now than it did 40 or 50 years ago. Specifically, 6-9 degrees below normal is less cold than it used to be.

Look at the graph below to see what we're dealing with here.  This is the threaded record at Minneapolis, back to 1872.  The 2013-14 winter is labeled, with an average Nov-Mar temperature of 17.5 degrees F, the 11th coldest on record.
This winter was the coldest since 1935-36, but if we agree not to split hairs, you can see that seasons like it were common from the 1950s through the 70s, and that even colder ones were pretty routine in the first 40 years of the record.  If this winter had happened in either one of those periods, no big deal; it would have been among peers.

But that's not the case. It has no peers in the recent record.  And so that brings us to talking point #1, which is true for much of the US also:

  • Yes it was cold, but winters like this used to be more common, though not in the most recent 30-35 years. Indeed, the lack of anything like it recently is what made it so unusual.
There's a lot more to say about this winter, and how it fits in with recent ones.  Coming soon!

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