May 25, 2009

Sound Breeze!

During the warm season, the subtleties of local weather are to be savored, and none is more frequent than the Sound Breeze.

Official definition: the Sound Breeze is the northerly wind that develops during the midafternoon over the northern half of Puget Sound and which maintains itself until approximately 8-9PM. Over the central Sound the breeze can blow 15-20 knots, with less winds over land.

The sound breeze is important for everyone like to sail, fly kites, or bike home after work. Many an afternoon I have to bike right into it...slowing me down considerably. And it makes kite flying wonderful during the late afternoon at kites hills at Magnusson or Gas Work parks. And it is heaven for early evening sailors.

The Sound Breeze is really a big sea breeze circulation. Remember the sea breeze? Cool, ocean air moving towards the heated land during the day? In this case, we have the Strait of Juan de Fuca and Georgia Strait full of water and the Puget Sound basin mainly land. As the PS basin heats, the pressure falls and the northerly sea breezes pushes in.

Above are two maps of surface winds on May early in the day and the other at 4 PM. You can see a real strengthening of the northerly flow in time..the Sound Breeze in action.


  1. Heaven for sailors, but not so much for powerboaters. :)

  2. I must say I am missing the more frequent posts.

    I am wondering why hot temperatures in May are labeled as "abnormally high" when it seems to me that we can pretty reliably predict a string of hot, 75 degrees-plus, days in May almost every year. Is this based on average daily temperature for the whole month? In that case, cold temps in early May would be "abnormally low".

  3. Max temp stats: xmACIS database gives me an average of 3.5 days of 75 degrees or higher in May. Data goes back to 1948. In 1958 and 1992 there were ten days, but coming in first was May 1995 with 14 days with a max temp of 75 or better. 1955, 1962, 1965, 1974, 1977, 1991, 1996 and 2000 all show no days of 75 or better. So far this year two days, plus a couple or several more looking likely. June thru September averages are 7.1, 15.5, 14.8, and 7.4 each, and the rest of the months thru April have less than a day. 48.6 is the total for an average year.

    The '09 May mean temp should come out pretty close to average after a few more warm days, -0.7deg as of now, but with an extra 2" of rain in the bucket.

  4. Cliff, great blog!

    I spend a fair amount of time on Puget Sound racing sailboats, where we can usually count on the northerly “Sound Breeze” during good weather. At a regatta last year (May 17, 2008) on Shilshole Bay we witnessed a really odd wind phenomena with what appeared to be southerly “Sound Breeze”. This particular weekend was characterized by abnormally warm weather (80+ degrees) and a fairly consistent southeasterly breeze that built in velocity throughout the day, similar to the typical northerly "Sound Breeze" described in your post, but coming from the south not the north. Any thoughts on this; ‘HOT Shilshole southeasterly’? Maybe, just a localized thermal breeze? Or could this unique event been based on the unseasonably warm early May temperatures?

  5. Thanks, Mike! Those stats totally ring a bell for me. A few 75+ days in May, more in a good year, few more in June, better July and August. September is a little better than June. By better, I mean I like the heat but rather it was closer to 75 than 80. :)


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