PROSSER, Wash. - Following a winter of wild weather extremes, springtime in central Washington was the wettest and windiest since 1990, according to data recently analyzed by Nic Loyd, Washington State University meteorologist, and Gerrit Hoogenboom, director of WSU AgWeatherNet.   Following periods of unusual warmth in January and February, a large-scale pattern change occurred in late February and yielded one of the coolest springs (March-May) in central Washington in 20 years. The most notable aspect of the spring weather was the length of the cool spell and the consistency of the large-scale pattern.  

Show me the numbers

People talk about it being wet and cold, but we always want to see the numbers. And what those numbers show is that it was indeed cold, wet and windy, said Hoogenboom. Weve made the numbers available in the form of a summary review that is posted on our website.    

Below normal temperatures

March, April and May featured below normal temperatures and unsettled conditions over the region. A strong jet stream transporting cool north Pacific Ocean air masses into the region, coupled with cloud cover and evaporative cooling caused by rainfall into dry air, led to very cool average daily maximum temperatures of 60F.   In contrast, daily minimum temperatures were relatively less cool due to many cloudy, moist and windy nights that inhibited surface heat loss. At an average of 6 mph, wind speeds were unusually strong during the 2011 spring.  

Crops get late start

A consequence of the unusual spring weather has been a late season for a variety of Washington crops:

• The spring wheat crop is more than one week behind, and many growers were unable to plant due to saturated or flooded fields.
• The cherry crop is about two weeks behind but is expected to be larger than normal.
• Progress at area vineyards is lagging by one to two weeks, but a warm summer may allow the crop to catch up.

Snowpack levels

The June 23 opening of Chinook Pass, near Mount Rainier, was nearly one month later than normal due to a heavy snowpack and cold spring weather. The large snowpack is beneficial to central Washington growers and will contribute to an abundant water supply this summer.   Heavy rainfall in mid-May led to significant flooding along the Yakima and Naches rivers, and snowmelt is leading to a continuation of high water levels on central Washington rivers.  

La Niña

The cool and wet spring, which included significant late-season snowfall in the Cascade Mountains, was somewhat expected due to the presence of La Niña. La Niña is the negative phase of the El Niño-Southern Oscillation (ENSO). ENSO is characterized by variations in the phase and strength of the Walker Circulation.   The Walker Circulation involves a coupled ocean-atmosphere circulation in the equatorial Pacific Ocean that varies in phase over time periods of several years. La Niña is characterized by strong east winds and cool sea-surface temperatures in the eastern equatorial Pacific Ocean.   Although ENSO generally moves between positive, neutral and negative phases over two to five year intervals, it cannot be forecast more than a few months in advance, so the magnitude and duration of individual events cannot be estimated beyond one years time.   Based on maximum observed three month sea-surface temperature anomalies in the east-central equatorial Pacific Ocean this past winter, this La Niña event was moderate to strong and seems to have significantly affected the weather in the Pacific Northwest.   La Niña often exerts its strongest influence over the regions weather during the winter and springtime via teleconnections. Teleconnections involve correlation between climates in different regions of the world.   The variations in the tropical circulation and sea-surface temperatures affect the planetary waves that govern Pacific Northwest weather patterns. Generally, stronger La Niña events have more significant and predictable effects on the regions weather.  

El Niño-Southern Oscillation

However, ENSO exhibits limited value regarding warm season climate predictability. But it appears that the ENSO neutral conditions that have developed recently may continue, so the long-range forecast for next winter remains anyones guess.      

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