April 2011 — unexpectedly cool and wet

Weather Matters   May 1, 2011

Yep. I said it. No denying it. And nobody will let me forget it.

“April – average temperatures, below average precipitation”

That was my forecast, a month ago. The reality? “Below average temperatures, above average precipitation.”

Oops!

As of the 29th, the average high temperature for the month of April at the local Hyslop Experiment Station was 56.3 degrees F, a full 4 degrees below the long-term average, or “normal.” The average low temperature, 37.2 degrees, was 2.8 degrees below normal. In the last 30 years, only one April was colder than this year’s – in 2008.
Total precipitation was 4.03 inches, compared with a normal of 3.09.

And all that cold and wet weather is translated into “lots of snow” in the mountains. From an article by Stuart Tomlinson in the Oregonian April 29:

“Oregon’s snowpack, which typically peaks around April 1, continued to grow during the month and got an additional boost late Wednesday and Thursday with more than a foot falling at pass levels in the Oregon Cascades. Snow levels were down around 1,500 feet.

As of Thursday afternoon, total rainfall for April in Portland moved from the fourth-highest to the third-highest in 71 years. At 4 p.m. Thursday, the total rainfall at Portland International Airport reached 4.84 inches, 2.2 inches above normal.”

Steve Pierce, vice president of the Oregon chapter of the American Meteorological Society, released a list of records or near-records that have been set, threatened or broken around Northwest Oregon this spring:

— Astoria still hasn’t reached the 60-degree mark this year, crushing the “latest first 60” set on April 19, 1945.

— A record for the latest “first 60-degree day of the calendar year” in Portland came on March 31. The old record was March 27, 1955

— Portland has received measurable precipitation of at least .01 inch on 48 of the last 61 days, including 23 days in a row in March. March’s total rainfall of 6.43 inches made it the fifth-wettest on record.

So what’s going on, and how did I blow the forecast so badly? I wish I knew.

Ultimately, I think we can pin the blame on the ongoing La Niña (cool event) in the Pacific. The problem is, I based my forecast on what is “supposed to happen” during a typical La Niña, and this one was anything but typical. A La Niña winter is “supposed to be”:

Fall – relatively dry and mild

Mid-winter (Dec. – Feb.) – wet, wild, windy

Spring — relatively dry and mild

Last winter started out in typical fashion, with a slightly drier-than-normal November and a very wet December. So far, so good. Unfortunately, since the first of the year, things have been backward. January and February were quite a bit drier than average, while March and April have been very wet. And cool.

And I’m reminded of 1997, a year with a big El Niño event in the Pacific. I issued my annual fall-winter forecast in August, as I have done for many years. But that year, I got smug. Buoyed by a very successful forecast the previous winter, in which I divided the winter up into “first half” (Oct. – Dec.) and “second half” (Jan.-Mar.), I decided to issue a prediction for each month.

My composite forecast (warmer and wetter than normal) was right on. Yet I got every month wrong! This year is similar. I expected a wetter, cooler January and February, and a drier, milder March and April. In the end, it all balanced out. I got the right answer – somewhat wetter and cooler than normal – for the wrong reasons!

I’m a bit gun-shy about looking ahead, but I’ll go ahead and make a prediction: things will warm up considerably by mid-May. June and July will be warmer than average. Summer will come!

And if I’m wrong, I’m sure I’ll hear about it!

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