Weather Blog

A bunch of heat wave statistics

A bunch of heat wave statistics

(I've updated this Monday morning since its original post on Friday for some new statistics)

As some forecasting models continue to suggest the upcoming heat wave could rival some of the worst on record, let's look at what it's up against:

The longest stretch of days at 90 or hotter was in August 7-11 of 1981, when we had a stretch of 91, 93, 99, 98, and 93.  This also qualifies as the hottest week in Seattle history, as those five days were book-ended by 86 degree readings, giving it an average high of 92.3 degrees. We also had a stretch of 5 90s+ in 1941 when records were kept at the Downtown Federal Building.

There have been five times when we've had stretch of four days at 90 or hotter -- the most recent was July 21-24 in 2006, when it was 98, 96, 95 and 92.

But arguably the worst extended heat wave was in 1977 (one of those four-day 90+ stretch years) and this is the one this summer will likely compare to when all is said and done.

During the 18 day stretch between July 31st and August 17th, every day save for the 14th was over 80 (the 14th was 79), 14 days were at 85 or hotter, and six days were over 90, including a four day stretch of 90, 93, 93, and 95, followed four days later by another 93 and 95 degree day.

(Incidentally, once that heat wave broke, the rest of the month was very cool and rainy and they actually ended up with the third wettest August on record.) 

So far, we're not quite there yet -- since July 16th, we've had days of 87, 90, then a three day break before going back to 87 again on the 21st, but we'll see how this stretch stands when we get to the end of next week.

Other heat wave of note: On July 20, 1994, we hit the all time record high of 100 degrees, then went 93 the next two days.

Could Seattle Experience Their Warmest Night Ever?

One other record to watch: There has never been a day ever -- EVER -- where the temperature has failed to drop below 70 degrees in Seattle at some point during the day. That incluldes the Downtown Federal Building records back to 1891.  In other words, the warmest overnight low temperature on record is 69 degres, set Sept. 2, 1974. (September!?!) The high that day was 91.

Many of the foreasted low temperatures this week are in the upper 60s for Seattle, but it would not surprise me to see a 70, especially if we get near 100 and a warm, east wind blows through the night.

Play Along At Home:

Here is a chart that shows three of the hottest days in Seattle history (July 20, 1994 (100) July 21, 2006 (98) and August 9, 1981 (99)) and how hot it was each hour. Compare to the current temperature which you can find here

Time 7/20/94 7/21/06 8/9/81
Eventual Hi Temp: 100 98 99
8a 73 72 74
9a 77 75 79
10a 79 79 83
11a 81 84 87
Noon 85 84 91
1p 88 88 94
2p 90 90 97
3p 94 94 99
4p 98 96 99
5p 99 96 99
6p 98   98

Some other interesting tidbits:

  • In a normal Seattle summer, we average 25 days a year at 80 or hotter, 10 of those 85 or hotter, 2 of those at 90 or hotter, and a 95+ every other year.  As of Friday, we're at 17 for 80+, 9 for 85+ and 2 for 90+.
  • Most number of days in a year at 90 or hotter was nine in 1958. On the other hand, we went through the three summers of 1999 to 2001 with no 90s. (Or as I call them: "The glory years" :) )
  • Seattle has hit 100 just the once on July 20, 1994. We've hit 99 twice -- Aug 9, 1981 and July 23, 1991. We've hit 98 five times, including, as you saw earlier, the day after we hit 99 in 1981.

Upcoming Record Highs:

  • Mon. July 27: 95, 1988
  • Tue. July 28: 97, 1988
  • Wed. July 29: 95, 1971
  • Thu. July 30: 94, 1960