October has been on quite the sunshine kick. We've already had one full-week of dry weather from Oct 1-7 and if the extended forecast holds up, we'll complete another 7-day dry streak by the end of this week -- almost summer-like dryness! (Never mind that 2+ inches of rain in between the streaks :) )
As for sunshine, on a scale of 0-10 for sunshine (0 is clear, 10 is overcast), October is averaging a 6.1 through Sunday. That's better than September and June (both 7.6) and not too far from this past August (5.4). July remains king at 4.7.
For many, these nice stretches in the middle of autumn are colloquially known as an "Indian Summer." Up until today, I thought the term was pretty informal to mean any kind of nice sunny and relatively warm stretch, and so I'd have thought this current streak would qualify.
But I received an e-mail asking since it went below freezing at their home over the weekend, does this sunny streak make an official Indian Summer?
"Official" Indian Summer? Lo and behold, apparently there are some criteria you're supposed to meet, at least according to a few online sources.
One of the more credible sources would be the Farmer's Almanac. Their definition of Indian summer is a period of at least 70 degree weather for 7 days or more after the autumnal equinox.
That's a rough national definition, but doesn't really hold water here because that would be a real climate shocker to go 70 degrees for a week or more this time of year. (Insert joke about how it would have been a real climate shocker to see a week straight of 70+ in August in Seattle this year.)
But there is a second tenet for New England -- the warm stretch has to come after the first hard frost of upper 20 degree temperatures. You can see why we're not in that boat since 20s in October are quite rare -- record lows range from 28-33 this time of year in Seattle. But that's probably what prompted the e-mail since lows were around freezing in the outlying areas Sunday morning (37 was the low in Seattle).
So what should qualify for Seattle and the Puget Sound area? Maybe we just keep it informal, but I'd say a dry stretch of weather over 65 degrees should qualify, in which case, this current stretch is too cold with highs in the mid 50s to low 60s. (Average highs are in the upper 50s as of today, but this time of year, every three days our average high temperature drops a degree.)
And I'd base it more on dry than cold temperature. Like a dry stretch of 3 or more days at 65 degrees after a period of at least three days of rain. That's pretty rare :)
If you're wondering how it got the term "Indian Summer", there doesn't seem to be a consensus over its origin. The Farmer's Almanac presents two possibilities: One: Early American settlers mistook the sight of sunrays through the autumn haze as Native American campfires -- not sure I buy that one. The second is that Native Americans recognized the pattern as time to gather for winter.
There's plenty more out there -- I am loathe to buy anything on Wikipedia, but there are some guesses there too.
If you crave even more info on the subject, Check out this story posted on the National Weather Service office page in Detroit, Michigan. Not exactly the most relevant to Pacific Northwest climate, but an interesting read.
From Indian Summer to La Nina Autumn
Whether or not you want to count this as an Indian Summer or not, it's about to come to an abrupt end. The weather is expected to take a turn to the stormy for the end of the week and this weekend, with perhaps a good soaking storm Saturday night into Sunday. That's courtesy of the remnants of Super Typhoon Megi, which is just finishing pushing through the Philippines and its moisture is about to make its hyperspeed trek east across the Pacific.
So get out there and enjoy the sun now!