July 24, 2013

Secret Revealed: The Northwest Has the Best Summer in the Nation. But Why?

The secret is out. 

A few days ago, a well known ratings group found Seattle to be the NUMBER ONE city in the U.S. for pleasant summer weather, while Portland followed in second place.  Even major newspapers like the Los Angeles Times seemto agree.  A table from the authoritative Sperling report says it all (see below).   With comfortable average highs in the mid-70s, sleep-friendly lows in the lower fifties, and low dew points and relative humidities, Seattle is meteorological heaven during the summer months.

(Dew point is the most important measure of the amount of water vapor of the air.  It is temperature to which air must be cooled (at constant pressure) to reach saturation.  The eastern U.S. often gets into the mid-60s and 70s F.  We stay down in the lower 50s or less.  Above around 60F the air feels sticky and humid for normal temperatures.)

But the Sperling report missed some critical meteorological and other information that makes Northwest summers even closer to heaven on earth! 

(1)  Being relative far north we have the longest days in the lower 48 states.  So there are more hours to enjoy perfect weather.  Finish work at 6 PM?  No problemo...plenty of time to have fun outside.

(2)  When we do have one of our "heat waves", it is nearly always DRY HEAT with low dew points.   Why?  Because to get really warm here, you have to get offshore, downslope flow.  Air coming off the cool Pacific is obviously not going to give you a heat wave.  The interior of the Northwest is dry and when the air sinks along the western slopes of the Cascades it is compressed by higher pressure and warms.  It is virtually IMPOSSIBLE to get a major heat wave (temps above 95F) with high humidity as they get in the eastern two thirds of the country.

(3)  Other parts of the country can get severe thunderstorms during the warm season.  That is extremely rare around here because of the cool Pacific and low dew points we enjoy.

(4)  We do not get hurricanes or tropical storms like the eastern U.S.  Again, thank the cool Pacific Ocean.

(5)  We have practically NO RAIN in the summer.  Really.  Seattle is drier than Phoenix in July. So you can enjoy perfect temperatures without the inconvenience of even thinking about an umbrella or rain gear.

(6) We have far fewer mosquitoes and biting flies that the eastern U.S. ?(probably the lack of rain contributes to that!).  And did I mention a lack of poisonous snakes!

(7)  Seattle has great visibility in the summer.  This is because the air is relatively clean after passing across the Pacific and our low humidity (which prevents particles that absorb water vapor from growing).  And we have great things to see as well, like the Cascades, the Olympics, Puget Sound, and Mt. Rainier.

(8)  If you don't like the perfect weather of the western lowlands, a short drive can give you something a bit different (but still good!).  Head to the coast if you would like to take 10F off the temps and enjoy the sound of a few fog horns.  Cross the Cascades for that dry, warm sauna effects at Lake Chelan or other locations.   Perfection plus choice.

(9)  In the Puget Sound lowlands escape from heat is only a short drive or bus ride away.  The Sound is still around 50F during the warmest spells and the beach areas can be in the 60s, while 80s or warmer are found a short distance away.

(10)  It is hard for us to stay too hot for too long.  The NW has a natural air conditioner system.  As temperatures warm, pressures tend to fall over the hot interior.  Eventually the pressure difference between the cool (and higher pressure) Pacific and the interior gets so large that marine air surges in.  And profound relief follows.  Virtually guaranteed.

(11) And even when we have our biggest heat waves, nighttime temperatures are still reasonable.  Consider the WARMEST DAY IN SEATTLE HISTORY, when temperatures at Seattle Tacoma Airport climbed to 103F.  The temperature dropped to 71F that night!  A bit warm, but still ok for sleeping if you have a fan.  Folks on the East Coast call that a comfortable night, particularly since our dew points were modest. 

Yes, we live in as close to summertime meteorological nirvana as is available on this planet, a fact the Seattle Chamber of Commerce should use to our great advantage in the tourist trade.  And there is another deep secret:  because of our proximity to the Pacific the impacts of global warming on local summer weather will be far less than in most areas of the country.  We will remain meteorologically blessed.

The Path to Seattle During the Summer


  1. Excellent post, Cliff. Seattle is truly spectacular in the summer.

  2. I am very surprised that Milwaukee-Waukesha-West Allis , Wisconsin, comes in at # 8 on the list. While it does have its fair share of beautiful days with low dew points and highs in the upper 70s and low 80s, there can also be relatively long heatwaves when temperatures reach the 90s (or rarely the low 100s) and dew points hit 70-75 degrees. It can get pretty uncomfortable. The month of September and often much of October is perfection in southeast Wisconsin, however. I'm from Wisconsin but now live in Astoria, Oregon. This summer has been nothing short of perfection, even here on the coast. (light years better than summer 2012)

  3. The winters aren't bad here, either. Check out Iowa in January and you'll understand what I mean.

  4. So yay, and I will remember that during the 4 twenty drive home in the 3rd week of January somewhere in Portland.

  5. I would add that it probably should be said that this great summer weather is for a somewhat restricted portion of the Pacific Northwest -- even though of course the most populated -- namely, the I-5 corridor. And even there you need to be careful, and probably cut it off where the Willamette Valley ends, as Medford, for instance, gets awfully hot for significant periods in the summer. This year, even Eugene has been noticeably warmer than Portland.

  6. Jeez, guy, you don't have to tell the whole world. Now they will all want to live here.

  7. Where are they getting a nighttime low temp of 52.9F for Seattle? SeaTac averages a low temp of 56F during July/August.

  8. Emmett Watson would not be pleased with this days blog Cliff.

  9. no mosquitos... really. obviously whoever wrote this hasn't been in washington recently.

  10. Pony, you sure you should be driving at that time of day?

    (sorry, I had to)

  11. It's not that there are *no* mosquitos in WA, it's that their numbers are severely limited compared to almost anywhere else in the country. For instance, I grew up in Maine, where the summer air temps aren't much warmer than here, but the humidity is *much* higher, and it rains frequently in the summer.

    You don't go out after 4pm there unless you first douse your entire body in bug spray. Mosquitoes, black flies, horse flies, deer flies... it's like being attacked by a fleet of tiny, blood sucking helicopters. And don't get me started on the ticks. UGH.

    When I first moved here 15 years ago, I couldn't believe that the stores didn't all stock quart-sized containers of bug spray, and most people in the city didn't even have screens on their windows. And then I quickly realized why.

    Damn, I love Washington.

  12. I am also originally from Milwaukee, and am also surprised that Milwaukee is # 8 on the list. One possible explanation is that, if the official temperature readings are taken at Milwaukee's airport, that may not be representative of those portions of the metropolitan area that are away from Lake Michigan. The lake exerts a fairly strong cooling influence, and the airport is relatively close to the lake.

  13. Shhhhhhhhhhh. There's already way too many transplants here. Stop giving away our best kept secret.


  14. Of course Seattle may be under water with global warming ... meanwhile, if it came to it, you could get air conditioning.

  15. I have lived in 11 climatologically diverse states, and overseas for a time. I relocated to Seattle last Fall and this is my first summer here, and I'd have to say that personal experience matches the assertion that this is the best summer weather.

    I have been raving about it to friends and family members . . . truly the most spectacular summer weather I have ever experienced. I recognize that this summer has been running warmer than normal, but if I were to account for that, then "normal" would be even better.

    I guess the question I ask is whether the overcast, wet, cruddy weather for many months of the year (coupled with 8 AM sunrises and 4:15 PM sunsets; which of course you never see because it is almost always cloudy) is an appropriate price to pay for a few weeks of meteorological bliss in the summer. I'll say "yes" today but ask me again in February.

    1. My answer would be yes, because that wet winter weather with short days is still far superior to the bitterly cold snowy winters we had back home in the Midwest.

  16. Regarding point 2- almost, but not quite impossible. I'm farther south, Willamette Valley, but we had a series of three days in 2009 with temps over 100, and DP's in the mid-60's. Don't recall details of what was going on, but that was one of the most miserable stretches of summer I've experience in Corvallis. And of course, few have air conditioning. http://outsidetheinterzone.blogspot.com/2009/07/better-than-last-two-days.html

  17. They got Denver quite wrong. Denver's average highs in summer are 89. Though areas outside of DIA are slightly cooler.

  18. Spokane probably ranks high on that list as well.

  19. Forgive my ignorance, but how does one see the satellite imagery of WA state from space? I'm interested in seeing the fires. Thank you.

  20. I live in Austin TX. I spent 3 weeks in the Seattle/Portland area. Im sold. Im going to make it my annual get-out-of-Texas July event!

  21. Fairbanks, Alaska has very pleasant summers. It actually can get rather warm. But the -40f winter days are rough...especially with only a couple hours of sunlight.

  22. In the spirt of Emmett Watson I will offer some contrast:

    A few thunderstorms would provide entertainment, water the garden, and if there is enough rain, suppress fires.

    It's hard to find water warm enough to swim in.

    Sometimes (though not this year) summer does not start 'till July.

    And yes there are few bugs, though also there are no singing insects. Why there are few bugs in something of a mystery to me.

    Don't get me wrong- I am enjoying this! But there is another side to getting no rain at all. Fires don't often happen in the Eastern forests.

  23. Only Spokane is better! Warm enough to swim and enjoy the many lakes, but everyday is clear and dry. The sky virtually sparkles with clarity!

  24. Yep. Also having grown up on the northeast coast and northern Europe the truth about winter is the westher is not that bad. The worst thing is that the days are short so the winters are dark - again because of the northerly latitude.

  25. Seattle and the Northwest I-5 corridor's weather is called Marine West Coast. It compares to the climate of NW Europe: London, Amsterdam, Paris, Wales. Same thing.

  26. Although this is an older post of yours, Cliff, could you help me understand what makes Seattle's (or any place's) dew point lower that other areas? Moisture and relative humidity I get, but what are the magic forces that determine dew point? Thanks!!

  27. How is Duluth, Minnesota omitted from the list? It has just as cool of a summer as Seattle with bonus thunderstorms and much less people.


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