The coldest winter in a generation for the Pacific Northwest

The complaints have been endless: folks are tired of the cold, wet weather over the Pacific Northwest.   Many suggest this has been the coldest winter they can remember.

And if they are less than 32 they may be right--this may be the coldest year they have experienced.  The coldest winter in a generation!  And I will try to prove it in this blog.

Lets "warm up" by looking at the departure from normal of maximum temperature for the past two months.   Holy icicles!  Most of Washington State has been 4-6F below normal, and 6-10F below normal in eastern WA.  Eastern WA has been crazy cold and snowy this winter.

You know that "hotbed" of political intrigue in our state capital of Olympia?  Thursday evening's 53 F at Olympia broke a stretch of 19 straight days without reaching 50 F from 18 Feb - 8 March 2017.  By contrast, during the same 19 day period a year ago in 2016, 17 of those 19 days reached 50 F at Olympia.  What a difference a year makes.

The Midwestern Regional Climate Center has a Accumulated Winter Season Severity Index (AWSSI) that will take your (cold) breath away (see below).  This index consider such parameters such as cold and snow and how conditions have deviated from normal.  Seattle has had severe winter conditions and eastern Washington/eastern Oregon/Idaho have experienced an EXTREME winter.  As bad as it gets.

This is getting scary.  So let's do some analysis ourselves and determine how unusual the December through February temperatures have been for our region. And let's use numbers from the official NOAA ESRL web site (which I hope the current administration doesn't defund).  

Here are the average maximum temperatures (for Dec-Feb) for the past 70 years.  OMG.  This year was the coldest since 1985!

What about the high temperatures in the Columbia Basin around Richland?  This winter was the coldest since  1985 (although 1993 came close) and only the stunningly cold winter of 1949 exceeded it in a significant way.

So why have we been so cold?

The first thing a meteorologist does is to check out the atmospheric circulation anomalies (difference from normal).  Has the atmospheric flow been unusual?   The answer is yes!   This figure below shows the upper level (500 hPa) height anomalies (like pressure anomalies).  A large negative anomaly (which means low pressure or heights) over the Northwest and a higher than normal pressure over the Gulf of Alaska.  That pattern brings colder air into our region (and stronger flow into California, thus their bountiful rain).

This pattern suggests an alternating series of highs and lows, which implies a "wave train" propagating out of the tropics.   That in turn was probably produced by anomalous convection (thunderstorms) in the tropics.  There is no reason to suspect global warming is associated with this. And no reason to suggest that this cold winter over the Northwest is a reason to be skeptical about human-caused global warming.

And, one more thing.   An anti-blob has been in place off our shores, with colder than normal sea surface temperatures shown by the blue colors on the following graphic (the sea surface temperature anomalies for the past three months).  That cold water was probably the result of the anomalous wind pattern.  Cold offshore water probably helped to cool our temperatures by a small amount.

The cold winter has definitely had an effect on plants, with a lot of spring foliage changes being delayed (such as the cherry blossoms around campus).