2011: The Year Without a Summer?

Here in the Pacific Northwest June has given way to July, but judging by the chill outside this morning it could have been April. The calendar shows us that it is clearly summer; technically this cannot be denied. Yet, for a region recently gripped by an icy La Nina winter, followed by one of the coldest, wettest springs on record, summer, and the typically warmer, drier weather associated with it could not arrive soon enough.

After much La Nina related fanfare, the winter of 2011 started not with a bang, but a whistle. The Cascades, although having caught some early winter weather late in October, would not sustain a snowpack until December. The weeks preceding the Christmas Holiday were fairly average for a Washington winter; some snow in the mountains, rain near the deck around Puget Sound and a mix of wintery bleh east of mountains. Then came “June-uary.”

At 11:50 PM, as 2010 prepared to turn the corner into 2011, precipitation atop Stevens Pass, one of the highest anywhere in the Cascades abruptly turned from snow, into torrential freezing rain. Warm, moist air travelling along an atmospheric current known as “The Jet Stream” had overrun a stubborn mass of cold air which had been perched east of the Cascade crest for days. The warm and productively wet weather systems associated with this sort of atmospheric activity are referred to as “Pineapple Express” events. These events are capable of producing immense amounts of precipitation, and when passing over an existing pocket of colder air can produce hours, or even days of the heavy mixed precipitation that our cute and cuddly weather-folks have recently taking to calling a “wintery mix.”

In a normal Pacific Northwest winter, let alone one where strong La Nina conditions exist, Pineapple Express events are few and far between. January 2011 saw four such events and more than 20 inches of rain falling in the Cascades.

In Late February, things changed abruptly. The current of warm, moist air that had persisted since early January was suddenly blocked by high pressure ridging, allowing cooler systems-- often associated with an Arctic boundary front, to enter the region from the north. These systems were wet and very cold, often producing lowland snow events, and are more characteristic of La Nina conditions. March and April shattered cold weather records throughout the state of Washington.

In May, cool and wet weather persisted ever on. Seattle was having one of the more dismal spring seasons that anyone could remember. In the Cascades, ski resorts already closed for the summer watched helplessly as they accumulated more snow in the month of May than in December or January.

June brought more of the same, as many locations throughout Western Washington had yet to record a 70 degree afternoon. The southwest Washington town of Chehalis tallied only 8 precip-free days between March 22^nd and June 14^th, a period perfectly capable of providing summeresque weather. Things were wet west of the crest, but the Eastern portion of the state was not spared.

Above: Temperature data out of Ellensburg, WA for the month of June 2011. Shown are daily high and low temperatures and their relationship to statistical mean temps. The red line is the mean high temp, the blue line the mean low.

-Graphic courtesy Cliff Mass Blog

 Statistically speaking the most likely time of year to see warm, sunny weather around Northwest is the second part of July and the first three weeks in August. The persistence of northwesterly flow aloft deep into the summer is very unusual. Chief regional meteorologists agree that this weather can’t last forever and that we will inevitably see some summer, at some point. Today, as Washingtonians hustle to make their 4^th of July preparations, the weekend forecast calls for some rain, wind and chilly evenings throughout the state. That sort of weather is not conducive to forest fires; music to the ears of the numerous Eastern Washington communities plagued by flames each summer.