Cold start to December

We are finally thawing from a strong early winter cold air outbreak.  Temperatures in the 30s never felt so warm, right?

The perfect setup for a cold air outbreak includes: (a) North to Northeasterly flow that directs Arctic/Continental Polar air that has been “chilling” over the frigid northern continent into the NW, (b) a white carpet rolled out ahead of the cold air outbreak from a landfalling winter cyclone that drops snow across the area and minimizes the amount of modification the Arctic air undergoes when migrating south, and (c) strong surface high pressure that allows for calm conditions and extremely low levels of atmospheric moisture. It further helps to have these conditions “locked in” for some time for a cumulative effect on low temperatures.

Much of the inland NW received measurable snowfall between December 3-5 during the transition between our typical maritime zonal pattern and the Arctic meridional pattern. Locations that avoided any appreciable snow got off the hook easier than their counterparts. One of the local cold spot in Northern Idaho and eastern Washington that did receive a couple of inches of snow was the Pullman airport which recorded 6 consecutive nights below 0F.

This is the longest streak of minimum temperatures of sub-0 temperatures  since the ASOS station began in 1998. This was not the case for longer-term stations in the area as colder events in early December occurred in 1972, 1922, and 1919. In addition to the ideal synoptic setup for cold temperatures mentioned earlier, the topography in the immediate vicinity of the airport allowed for air that is rapidly cooled at night (especially w/snow cover which is an effective emitter of radiation) to drain into the valley where the airport sits.

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The inland NW was is good shivering company as this cold air outbreak brought wickedly cold temperature to much of the contiguous US and associated hazards of snow, ice and power outages. While much news coverage across the country focused on the cold, Alaska was toasty (relatively). In fact, freezing rain was reported in Anchorage and Fairbanks as air temperatures near 5000-feet elevation were above freezing. The daily average temperature from December 4-8 was 7F, 7F, 8F, 0F, 0F at the Pullman Airport, while average temperature on these same days in Barrow Alaska was 15F, 9F, 18F, 24F and 23F (w/o an appearance from the sun at 71.3N). Yes, sometimes life is not fair.

A local cupcake and fro-yo shop called Sweet Mutiny in Pullman provides a humorous incentive to increase business during such cold times. See it pays to watch the weather.

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This harkens back to one of my favorite computer games as a kid on the Apple II called Lemonade Stand where you’d base your decisions on how many glasses of lemonade and their price as a function of the daily weather forecast (e.g., hot you sell a lot, cold and wet not so much). Promotions like the one by Sweet Mutiny this would have been a real wildcard in that game.

Don’t let the cold weather and snow cover fool you though. The cold air coincides with a typically very wet time of the year across the Pacific NW. This cold-dry regime has further contributed to the snowpack deficit where it really matters in our mountains. While snowpack in the Idaho Panhandle, western Montana and the Yellowstone area is on par, the Cascades and Boise Front Range are lagging.

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