Early arctic outbreak highlights December weather

By Rachel Webber, College of Agricultural, Human & Natural Resource Sciences

AgWeatherNet-logo-250PROSSER, Wash. – All that cold and nothing to show for it. Despite the bitter chill of early December, a lack of precipitation and bad timing have left the mountains low on snow for the start of 2014.

As of early January, the Cascade snowpack sits at less than 50 percent of normal.

Storms that did occur were weak and mild, and the end result was often light rain rather than snow. Consequently, what seemed like a promising start to the month ended in utter defeat.

“Unfortunately, the early December arctic outbreak represents a huge missed opportunity,” said AgWeatherNet meteorologist Nic Loyd. “During this dry winter, it would have been helpful to augment the mountain snowpack at a time when a major ingredient like cold air was already in place.”

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Ag likely not threatened by late cold

Though dry, the arctic outbreak was impressive. Highlights included a low of -12 degrees at Pullman on Dec. 8 and a nine-day period of sub-freezing high temperatures at Prosser. Pullman recorded five consecutive nights below -5 degrees, while Moxee fell below 10 degrees for an eight-night streak.

Even in western Washington, Mount Vernon experienced sub-freezing low temperatures for 11 consecutive days.

“Despite the frigid temperatures during early December, the agricultural impacts should be much less severe than what was observed in the aftermath of the Thanksgiving 2010 arctic blast,” said AgWeatherNet Director Gerrit Hoogenboom. “This recent cold snap occurred in December rather than November and was preceded by seasonally cool weather, which allowed many crops to acquire sufficient cold hardiness for the winter.”

6 inches of rain in a day

The only major storm of the month occurred on Dec. 1 and brought an incredible 6 inches of rain to Stevenson in just 24 hours. The last half to two-thirds of the month was characterized by weak systems breaking over a stubborn ridge of high pressure that was anchored just to the southwest of Washington.

One of the only other noteworthy storms occurred on Dec. 20, when the system brought early morning snow to part of western Washington and the Cascades before much warmer air flooded in and changed the precipitation to rain. Snow also fell in eastern areas near the Idaho border.

Temps below average

Monthly high temperatures at Prosser were only slightly below average thanks to several clear and mild periods during the middle to latter part of December. However, overnight temperatures were well below average due to the early arctic outbreak as well as a lack of mild nights for the remainder of the month.

Normally, active December conditions cause increased winds and mixing as well as persistent cloud cover and moist conditions. However, such was not the case this year. There were a sufficient number of clear and stable nights to allow for cold low temperatures despite a fairly mild upper level air mass during mid and late December.

The average low temperature at Prosser was 19.4 degrees, which is 7.2 degrees below average. In fact, the last time there was a larger (positive or negative) monthly temperature anomaly (mean, high or low) at Prosser was December 2009, meaning that 47 months had elapsed since the occurrence of such a significant departure from normal. Overall, 2013 featured the third coldest December mean low temperature on record (1989 to present).



Nic Loyd, WSU AgWeatherNet meteorologist, 509-786-9357, nicholas.loyd@wsu.edu

Rachel Webber, WSU CAHNRS Communications, 509-335-0837, rcwebber@wsu.edu