Heat waves are indeed rare in the Seattle area, but not unheard of.
I've just crunched more recent data up through July 31 of this year to get a better idea of how often we reach warm-to-hot temperatures, especially since it seems we've been hitting hotter temperatures more frequently these days.
This is for the 61+ years of data between June 7, 1948 and July 31, 2010 for Sea-Tac Airport.
With Seattle hitting 100 just twice in its history -- July 20, 1994 (100) and July 29, 2009 (103) we now average a 100 degree day or warmer roughly every 30.6 years.
For 95 degrees or hotter, it's about 2 out of every 3 years. (That has warmed a bit. It used to be every-other-year.)
For 90 or hotter, it's about 3 days a year.
For 85 or hotter, it's 10 days a year.
For 80 or hotter, it's 26 days a year.
These numbers have crept up a little. Before updating, I had the data up through 1997 and since then we've added about an extra 90 and 80 degree day per year.
But more amazing is that we've gone well over the 90 quotient just the past two years, reaching the mark 7 times in 2009, and already reaching it 3 times in 2010 before we even find out how this weekend's heat wave will shape up.
And since last July, we've hit 95 now four times -- three last year and once this year.
Even more interesting is a statistic unearthed by weather stat guru Jason Phelps. With our 95 degree reading this past July, it's the fifth year in a row we've had a day at 92 or hotter. Before this current streak, the longest streak had been three years:
2010: 95 so far
Then again, we went through a three year stretch in the late 90s when we didn't even get to 90. So maybe this is payback.
Anyway, stay cool out there!