By any measure, it has been a cold start to winter in the Pacific Northwest. It appears parts of Portland OR received up to a foot of snow last night. Traffic cameras show the snow belt extending well into southwest Washington State as well, even as far north as Olympia this morning. Seattle, my home, hasn't seen much snow this year. But it has been much chillier than normal for much of December and this first third of January.
How cold? Figure 1 shows that the average daily temperature has been 5-10 degrees below normal for much of the past month. Now, cold is relative. The normal average daily temperature in this part of the country in December and January is about 40F or so. So, even on days when it is 5-7 degrees cooler than normal, it is above freezing — although barely.
Nevertheless, it has been chilly, especially in mornings. My monthly gas bill from Puget Sound Energy came in the mail this Monday. It was almost twice its normal winter amount — for a number of reasons extending beyond just the coldish temperatures.
Figure 1. Departure from normal for daily average temperature, 2016+. Click to enlarge.
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The chart above shows the mean temperature for each day last year and its deviation from normal for any specific day based on 30 years of readings (in this case, readings recorded from 1981-2010 by the National Weather Service). Most of the past year has been significantly warmer than normal. Especially last spring which was noticeably warm and summer-like at times.
Figure 2 shows temperature departures from normal in Seattle across a much longer time span, from 2000 to early 2017. We've had other, lengthier stretches of cooler-than-normal weather recently, especially during the first half of 2011. But these cool patterns tend to occur later in the winter or early spring, so cooler-than-normal doesn't typically mean near freezing at these times. In fact, not only this year, but in more recent years, warmer than normal temperature days dominate.
Figure 2. Departure from normal for daily average temperature, 2000-2016. Click to enlarge.