What's the greatest daily temperature spread in Seattle history?
Spring time is a good time for some wide range in temperatures around the Northwest. The increasingly stronger sun as we get into the warmer months helps boost daytime temperatures, but then clear nights can allow that warmth to radiate right back out to space, making for nighttime lows dozens of degrees cooler than the daytime highs.
It's really noticeable in areas away from the moderating influences of water and the nighttime urban heating effects of metropolitan areas -- such as eastern Washington and Oregon where the days get even warmer but the nights get colder.
Earlier this month, we had that particular weather setup and the differences in temperature were quite dramatic. According to this blog by Prof. Cliff Mass some sites had 45-50 degree spreads in temperature!
That led one viewer to ask what is Seattle's all-time greatest spread between its daily high and nighttime low.
It turns out, while many areas get the dramatic changes thanks to plummeting overnight lows, for Seattle, amazingly, it was the other end of the spectrum: the greatest intra-day changes came on our hottest days with relatively normal overnight lows!
There is a three-way tie for the record, which is 40 degrees. It was first set on Sept. 15, 1951 with a high of 87 and a low of 47. It happened again Aug. 9, 1960 when the high was 99 and the low was 59. And then again on Sept. 14, 1974 with a spread from 88 to 48.
(Those curious about our 103 degree day on July 29, 2009 -- it was a much warmer night with a low of 71 - the only date in Seattle history the temperature failed to drop below 70 degrees.)
Those numbers are for Sea-Tac Airport, but for the older Downtown Federal Building records, the record is 38, also set three times, two from highs over 90 and the third a spread of 85-47.
But 40 degrees is nothing in many spots. Tucson has their spread in the 30s almost daily with a few 40s mixed in.
Over in the northern plains, they can get freak wind events called "chinook winds" that blast warm air through a chilly day. The winds come from a rush of air sinking down a mountainside, where it compresses and heats up -- much like how Seattle gets a summer boost in temperatures from an east wind -- only it's much more dramatic.
According to this site, the town of Spearfish, South Dakota had a day on January 22, 1943 where the temp went from -4 to +45 in two minutes (49 degrees!) The temp eventually climbed to 54 but 27 minutes later was back to -4.
The site says the world record for one-day change was set in Loma, Montana where they had a 103 degree change -- from -54 in the morning to +49 by the end of the day. Wow.
But in Seattle, being next to Puget Sound with a usual heavy influence from the cool Pacific Ocean does keep our nighttime lows from getting too chilly, and our daytime highs from getting too warm. So rare is the day when you need the heavy coat over the short sleeves.