Office of the Washington State Climatologist

The Winter of 2016-17 in Washington State

Many residents of Washington state are probably looking forward to some warmer and drier weather after this past winter. In a nutshell, it was cold and wet. It may have seemed especially chilly because our past few winters have been warmer than normal. The objective of the present piece is to provide some specifics.

We first focus on temperature, in particular the mean temperature anomaly pattern for the months of December 2016 through February 2017 (Fig. 1). This map is for the entire lower 48 states of the US to illustrate that in terms of anomalies, we were the coldest state in the nation. More quantitatively, for the three months WA had a statewide temperature anomaly of -4.8 F based on the climatological average for the years of 1981-2010. Moreover, the extreme negative anomaly on the whole map is indicated near the southeast corner of WA in the Snake River Valley. We’re Number 1! It bears noting that folks in the southeastern portion of the US are liable to have a completely different impression of the winter of 2016-17.

Figure 1: Mean temperature anomalies (F) for the period of December 2016 through February 2017 based on 1981-2010 climatological norms ‘
(from the High Plains Regional Climate Center).

While it was on the colder side, mean temperatures during the past winter were not nearly as cold as during some previous winters. This is shown in Figure 2, which represents a time series of statewide mean temperatures for the months of December through February back to the 1890s from NOAA’s National Center for Environmental Information (NCEI). For the entire period, the winter of 1948-49 takes the cake with an anomaly of -9.8 F. That being said, it has not been as cold in WA in an overall sense since 1992-93. One interpretation of the Figure 2 time series is that the magnitudes of the more prominent negative (and positive) anomalies have not changed all that much with time, but the frequency of these events has changed, with very cold winters becoming increasingly rare.

Figure 2: Washington state average temperatures for the months of December through February for the years of 1896 through 2017
(from NOAA/NCEI).

Getting back to the winter of 2016-17 itself, it was cold primarily because of the number of cold days, rather than the result of a few arctic-air outbreaks with extreme temperatures. In specific terms, of the 90 days of December 2016 through February 2017, Seattle (KSEA) and Spokane (KGEG) were colder than normal during 63 and 62 days, respectively. And the number of frigid days was also greater than normal, at least in the colder regions of the state. For example, Spokane dipped down to 0°F or below on 10 days, as compared with a long-term average of 4 times a winter.

The precipitation totals across WA state are also noteworthy. Here we take a longer view and consider the precipitation for the six-month period from the start of the water year (1 October) through the end of March 2017. The distribution of total precipitation for this period in terms of the percent of normal is shown for the northwestern US in Figure 5. By this measure, WA was decidedly on the wet side, especially east of the Cascade Mountains, but much of the rest of the Northwest did even better. The wettest months, relative to normal, for WA were October 2016, and February and March 2017, as detailed here and in previous newsletters.

We conclude this review with a short discussion of the significant short-term weather events of the winter of 2016-17. This discussion is brief because of the lack of prominent storms. To be sure, there were some especially cold, rainy and snowy intervals, and some winds at times. Regarding the latter, there were some blustery winds in the Northwest Interior region during times of cold Frasier River outflow, and some 100+ MPH winds.