Saturday, June 13, 2020

Are Weekends Wetter than Weekdays?

I have been hearing from a lot of folks suggesting that our weekends have been wetter than our weekdays, and asking me whether this was true.

So is it true?  Are the weather gods preferentially punishing Puget Sound residents over the weekend?

Are the weather gods punishing us?

Let's find out! 

To do this, I secured the daily precipitation statistics at Seattle-Tacoma Airport for May and June so far--43 days in all.

For the full period, there was 4.04 inches at Sea-Tac for .09 inches per day.

For the 31 weekdays, there was 1.72 inches in the rain gauge, or .05 inches per day

But for the 12 weekend days, there was 2.32 inches or .19 inches per day.

Yikes! It is true!  The weekends have been wetter, with nearly FOUR TIMES MORE PRECIPITATION PER DAY THAN DURING THE WEEKDAYS.

Good reason to complain.  But is this a real effect or just chance?

There have been a number of investigations of this serious topic, a recent one led by one of my ex-students:  Professor David Schultz of the University of Manchester.  Their conclusions based on examining the data from 219 stations across the U.S for the period 1951-1992 was:

"neither the occurrence nor amount of precipitation significantly depends on the day of the week"


A conclusion illustrated by this figure from their paper:


Other earlier papers have produced contradictory results.  Some have suggested that weekly variations in pollutants from industrial processes, aviation, and driving would influence precipitation processes, thus producing a weak weekly precipitation cycle.  But lets face it, such effects would be greatly minimized in this period of COVID-19 shutdowns and the protest-related fires did not start until late in May.  A plot of the concentration of particulates over Seattle does not suggest a weekly signal at all, with relatively clean air over Puget Sound for the period (see below, 5-10 is clean air).


I suspect strongly that this precipitation pattern is just bad luck, an unfortunately roll of the meteorological dice and will not continue into the summer.  Yes, it is raining today.  But according to the excellent weather.com forecast, tomorrow (Sunday) should be mainly dry, showers will be around Monday and Tuesday, and next weekend should be dry.


But providing an offering to your favorite weather god might not be such a bad idea, something meteorologists like myself are well practiced at.

In my department, we instruct the uninitiated how to appease the weather gods

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Good news to report.  Seattle parks and recreation has reopened the tennis courts, the athletic fields (for up to five), grills (up to five), and will open all the boat launches by June 20th. 

12 comments:

  1. Ha, nice. I've noticed that we've also been having cooler than normal temperatures as well as more precipitation than usual in this time of year... Interesting.

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  2. Old joke: "What follows two days of rain in Seattle? Monday."

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  3. If you look at the stats for several recent years before 2020,one will discover that the weekend weather was warmer/drier than the weekdays.It all evens out in the long run: Climatology.

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  4. Hello Cliff, On another note there has been a predominate Northerly wind this winter and spring. Is there a weather pattern that has effected our usual south winds? I live on Marrowstone Island. Eric

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  5. Lol! Lol! Yikes! When a meteorologist starts a sentence with Yikes...watch out!

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  6. “Protest related fires”? Influencing precipitation? Who was worried about that? A few cars and a few buildings across the country does not seem enough to even mention.

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  7. Thanks for addressing this, Cliff, despite what you said in an earlier post "some things are beyond my ability to answer"... But I stand by my cycle theory.

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  8. It used to be washing your car that did it ...

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  10. Great post Cliff! Looks like summer starts this Wednesday 6/17! Cold today in the mountains and blowing snow above 6000ft, must be cold up high. Hopefully this summer won't be too dry, if you could order a side of rain once a week to keep wild fires at bay that would be great :)

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  11. Yeah boat launches, tennis courts, etc opening up, but what is with closing the parking lots (both) at Matthews Beach over the weekend. Everyone ignored the no parking signs on the streets around the park on Sunday so that they could grab a piece of grass with their immediate friends and SD in the great outdoors that is the park.

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    1. Seattle Parks won't reopen its parking lots, so the public is doing it for them. Gotta remember to bring those bolt cutters next time ...

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