ACS Spring Forecast 2011 – and a Look Back at March

First, a look back:

After an amazingly wet March, it was a real treat to have mild (if not warm) dry weather for a change. March 31 and April 1 finally felt like spring had arrived. After slogging through the steady rains of March, it seems like spring is overdue.
“Steady” is right. Corvallis-Albany had more wet days (29 out of 31) than any previous March in our local weather history, which goes back 120 years. The old record was 28. Only the 23rd and the 31st were dry. The monthly total of  7.69 inches was more than 3 inches above the March “normal” of 4.61. Only six previous years have seen more March precipitation, led by 1904’s 11.70 inches. The last time we had such a wet March was 1983.

We also had a remarkable string of consecutive rainy days. Each day from February 28th through March 22nd had measurable rain – 23 days in a row!

Typically for such a wet month, the average high temperature was on the cool side (clouds blocked sunlight) and the average low temperature was above average (clouds kept temperatures from dropping very low at night). The average monthly temperature (average of all the daytime highs and nighttime lows) was thus very close to normal (46.5 degrees this year versus 46.7 for the 1971-2000 “normal”).

The first 60 degree temperature didn’t happen until March 31, which is unusually late. Portland Airport reached 60 the same day, also for the first time all year. This was a new record (previous record “late date for 60 degrees” was March 27, 1955).
Portland Airport ended up with the 5th wettest March since records began in 1940, with 6.43″ of rainfall for the month. The all-time record for March is 7.52″ set in 1957. According to Steve Pierce, measurable rain was recorded each day from March 7th through March 29th (23 days total); this was a new all-time record for consecutive rainy days in the month of March. “However, Portland fell just shy of breaking the all-time record for anytime of the year. That particular record was set in January of 1950 with 29 consecutive days of rainfall at the Portland airport.”

Meanwhile, in the mountains, snow has really been piling up. On March 1, the average snow water equivalent (water content of the snowpack) for the Willamette drainage was 90 percent of the long-term average for that date. By April 1, it had risen to 117 percent of average. It would appear that summer water shortages are unlikely.

Looking ahead to April, May, and June, I see big changes. Last year we had a very cool and wet period for those three months; this year, I believe, will be very different. I analyzed similar years in the past and found several years that had winter-early spring weather patterns similar to this year’s. The similar years are called “analogs,” and the idea is that “history repeats itself.” If, for example, we have a previous year whose January-February-March conditions (locally and over the Pacific) are similar to this year, we can conclude that this year’s April-May-June will be similar to those months in the previous years.

The analog years most similar to 2011 were 1956, 1971, 1974, 1979, 1989 and 2008. Looking at a composite of those years, we see…

April – average temperatures, below average precipitation:

May – average temperatures, below average precipitation:

June – below average temperatures, below average precipitation:


For the three months, near-average temperatures but below-average precipitation.

A far cry from March! “Below average precipitation” sounds great! I am ready for dry weather!

Plots from NOAA/ESRL

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3 Responses to ACS Spring Forecast 2011 – and a Look Back at March

  1. George: I sure hope you are right, but April sure is not cooperating yet. I am ready for a change.

  2. Mike D. says:

    George,

    Your analogous year method is probably correct, but are there some possible refinements? Such as limiting the prior years to those with strongly negative PDO’s and La Nina conditions? That might exclude 2008 and possibly some others, and change the outlook.

    • Mike-
      Yes, there are refinements. In my August forecasts for the fall and winter I have included PDO, and sometimes solar cycles. For this forecast I neglected those. I’m not sure why — just did!
      In looking at April so far, I’d say my temperature forecast looks wrong (I predicted average temperatures, but through the 15th Corvallis is 2.5 deg F below normal). I predicted slightly below-normal precip; total through the 15th was 1.31″ versus a normal of 1.49″, so that one is correct so far (with a dry week coming up!).

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