Mid-Willamette Valley Weather, 2010

Weather Matters
January 2, 2011

As we enter 2011, we can look back on a very interesting weather year in the Northwest in general and the mid-Valley in particular. 2011 promises to be just as interesting as 2010 – but different! Local observations were made at the Hyslop Experiment Station, between Corvallis and Albany just off Highway 20.

The year began with two very mild months. January’s average low temperature was the highest ever recorded here – 38.6 degrees F, a full 5 degrees above normal and 0.4 degrees above the previous record, set in 1995. The average high temperature was also on the high side, and if you average the highs and the lows, January was the 5th warmest ever.

“Normal,” you’ll recall, is a 30-year average of weather conditions, and the numbers are those recorded at our official weather station at Hyslop Experiment Station, on Highway 20 between Corvallis and Albany.

February was mild also. I believe the reason for the warmth was the El Niño event in the Pacific, which was beginning to wane. We tend to get our warmest winters when an El Niño is present.

But another characteristic of an El Niño winter is a tendency for them to be followed by relatively cool, wet springs. And, my goodness, that’s exactly what happened! It was one of the coolest, wettest springs ever. Things switched from dry-and-mild to wet-and-cool in March, and stayed that way until mid-June.

I decided to try to rank this year using a “cool-wet” scale. First, I ranked each year in terms of average temperature and total precipitation, selecting April-June as “spring.” So, for instance, 1911 ranks as the coolest with an average April-June temperature of 51.3 degrees and 1940 the warmest with an average of 60.3 degrees. Our data go back 115 years, so I would give 1911 a “coolness score” of 1 and 1940 a score of 115 (years of record). For precipitation, 1937 had the wettest April-June, with a 13.89 inch total; 1924 was driest with only 1.85 inches.

In 2010, April-June average temperature ranked 18th lowest all-time, while the precipitation was 5th highest ever. So for each year, I simply added the rankings. 2010 added up to 23 (5th highest precipitation and 18th lowest temperature). This produces an overall ranking, with April-June 2010 the 6th coolest-wettest year ever seen here. The last time we had a spring as cool and wet as this was 1991.

But spring gave way to summer – rather typical in most ways though a bit on the wet side – and El Niño gave way to a La Niña event. Our wettest, coolest winters usually occur during a La Niña, By the way, both El Niño and La Niña refer to situations in which tropical Pacific waters, especially those closest to South America, become warmer (El Nino) or cooler (La Nina) than average.

September and October were a little wet and a little cool compared with normal. Each had at least one day with more than an inch of rain. November continued the cool trend, but was a little drier than normal.

December, however, was quite interesting – also very mild and very wet. Monthly temperature was about 4 degrees above normal, and the rain was extreme – 10.25 inches for the month, nearly 3 inches above normal.

December’s rains pushed the total annual precipitation to 51.49 inches, well above the normal of 43.66. This was the 13th wettest year since records began in 1889. The annual average temperature, 53.0 degrees, was barely above the normal of 52.7.

Meanwhile, in Portland, according to Steve Pierce, the year brought:

  • The wettest calendar year since 1996 (nearly 15 years) with 46.18” for the year.
  • Wettest December since 1996 when more than 13” of rainfall soaked the area.
  • The Portland airport broke its all-time one hour rainfall record when 1.03” of rain fell in a single hour in early September. The previous record was 0.93” set in May 2008.
  • Wettest June on record with 4.27”
  • Coldest summer (June 1st through August 31st) in 17 years.

Finally, the strongest tornado to strike western Oregon or Washington since 1992 occurred in mid December in the town of Aumsville, Oregon. Many homes and other buildings were damaged, but no one was killed.

Happy New (weather) Year!!

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