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