Weather Blog

Summer was 6th worst in Seattle since 1948

Summer was 6th worst in Seattle since 1948
A skimboarder makes the best of a dreary day at Dash Point State Park in Federal Way, Wash. on Monday, September 6, 2010.

I know everyone is looking forward to the winter and what Mother Nature has in her La Nina bag of tricks, but let's pause a minute to take a look back at summer.

David Obelcz, one of our many local weather statistic gurus, annually analyzes both the summers (Summer Satisfaction Index) and the winters (Winter Misery Index) and rates them compared to all others. It's a tradition to post them here in my blog, and Obelcz was finally able to compute this past summer.

He says this past summer scored the sixth worst on his chart, which factors in variety of factors such as ingeniously giving extra weight to weather that occurs on weekends and holidays.

Here are his results, written by Obelcz:

After one of the nicest winters in Puget Sound history, Seattle suffered through its sixth worst summer in 62 years of weather records being kept at Sea-Tac Airport. 2010 was a Goldilocks summer -- we had too many days that were too cold, too many days that were too wet, and when it was warm, it was too hot. The number of nice days we had could fit in a baby sized bowl.

With a Summer Satisfaction Index of just 660.26, the numbers really speak for themselves.

  • There were 51 days where Seattle never broke 70 degrees.
  • There were four days where Seattle never broke 60 degrees, including a daytime high of just 56 degrees on June 20th.
  • There were nine more days were Seattle only struggled up to 70 degrees.
  • There were only 17 days where Seattle got over 80 degrees, and eleven of those days had area residents sweltered in 86 or higher degree heat, six of those over 90 degrees including two, three day heat waves.
  • There was an amazing 74 days where Seattle dropped below 55 degrees at night, including eight days below 50 degrees, with one night dropping down to a very un-summer like 46 degrees.
  • The first day of summer was 63 degrees, Independence Day was 65 degrees, and Labor Day only made it to 61 degrees.

But it wasn’t just too cold or too hot, summer of 2010 was wet by Seattle standards.

  • It rained on 42 days during the period, producing over seven-and-a-half inches of rain.
  • Nine of those days had more than one-quarter-inch of rain, and several rainfall records were broken, including 1.49 inches of rain on September 17th.
  • It rained on the first day of summer, Independence Day, and Labor Day.
  • It rained on 10 of 16 weekends during the 2010 summer season.


High Temperature: The ideal temperature range is 70 to 84 degrees for a high temperature. From 85 to 94 degrees there was a slight penalty, and for 95 and above there is a stronger penalty. From 60 to 69 there is a penalty and from 50 to 59 there is a strong penalty. There wasn’t a high temperature below 50 degrees for the model period. Low Temperature: The ideal low temperature range is from 60 to 69 degrees, above or below that range there was a weighting factor to penalize the range. Temperatures below 45 degrees gets a very heavy weighting penalty, temperatures below 40 (only happened on a couple of days historically) got an even heavier weighting.

Rainfall: If there was a trace of rain specifically, then there was a minor penalty. It is hard to determine from this data set if the trace of range comes from morning fog/drizzle that burns off or a cloudy gray day. The penalty grows the more rainfall that fell, with the maximum penalty happening after ½ inch of rainfall or more.

Days of the Week: Neutral range was Monday to Thursday. Friday got a little extra weight, as the weekend for most starts at 5 PM on Friday. Saturday and Sunday got the heaviest weighting.

Months: June gets neutral weighting; July gets increased weighting; August gets the highest weighting; and September gets a slight weighting bonus.

Holidays: June 21, 4th of July and Labor Day got a major weighting bonus. These are major days, but the model isn’t setup as such that a great 4th of July would hide an otherwise bad summer.

Sample Dates: The window of “summer” weather is from June 1 to September 20 to 22 (depending on when the autumnal equinox happens). Working with KOMO, the range of June 1 to the last day of summer was selected because many Seattleites start their summer activities by early June, enjoying long periods of daylight by the start of the month. For 2010 the Summer Satisfaction Index covers 113 days.


The model creates a score considering all of the above factors, with each day getting a score. The daily scores are added together for the summer season and totaled to give the result. The summer of 1948 is missing data from June 1 to June 7, as there aren’t any available records at Sea-Tac for those dates.


With a Summer Satisfaction Index of 660.26 this was the sixth worst summer since weather records were kept at Sea-Tac airport. The best year using this model was 1967, scoring an impressive 838.89. The worst year was 1954, scoring a 566.96. The average is 729.24. The summer of 2010 lowered the 62 year average, with 2008 replacing 1975 as the most average summer.