Winter was late arrival in Sisters Country

Weekend temperatures in the 70s mean spring is finally arriving in Sisters Country.

That makes it a good time to look back on the winter that was.

In December, no precipitation was recorded in Sisters Country until the last four days of the month, when two inches of water made its way into the rain gauge. But freezing levels were very high during this time, so except for the highest elevations, rain fell in the mountains too. December temperatures averaged about normal, but because skies were mostly sunny maximum temperatures were some five degrees Fahrenheit above normal while lows were about six degrees below normal.

January was warmer and wetter than normal, with almost all the precipitation falling as rain in Central Oregon. Temperatures returned to normal in February, but the month was dry in Sisters. It should be noted, however, that rainfall totals in Bend and Redmond were near normal. On February 27, two inches of snow was measured in Sisters, though more fell in nearby areas.

But winter didn't really get rolling until March. The month was three degrees colder and 1.3 inches wetter than normal as snow levels finally lowered. At the Sisters Ranger Station, weather observer Sandy Sharp measured four inches of snow on March 21; depths of eight or nine inches were observed in surrounding neighborhoods.

According to Marilyn Lohmann, hydrologist at the National Weather Service's Pendleton office, snowpacks in Central Oregon Cascade mountains were 75 percent of normal on March 1. By April 1 the snowpack had increased to just over 100 percent of normal. In the northern Oregon Cascades the snowpack is near 135 percent of normal. Snowfall depths are also far above normal in the Washington Cascades.

It turns out that the winter from which we are just emerging and the 2010-11 season had many similarities. Both were marked by moderate-to-strong La Niña signals that usually result in cooler- and wetter-than-normal conditions, with greater than normal mountain snowpacks. Typical winter conditions were slow to develop in both years, though the 2010-11 season got off to a good start in December before going dead in January.

A quasi-stationary ridge aloft effectively diverted Pacific storms from entering the region during the dead of winter in both seasons; it was a bit stronger in 2010-11. The cool and wet late winter and spring conditions, with ample snowpacks, is also similar.

Both winters were completely devoid of a single arctic air outbreak that usually produces a prolonged period of frigid temperatures. This appears to be unusual for back-to-back La Niña winters.

What lies ahead for the rest of our spring? According to the Climate Prediction Center, the three-month period from April through June should produce cooler- and wetter-than-normal conditions in the Pacific Northwest. If this forecast verifies, it should result in additional mountain snowpack, or at least reduced snow melt during the period.