May 16, 2014

Does Seattle Have a Weekend Weather Curse?

Many of you have thought about this.  

And increasingly I am hearing suggestions that it just might be true.

Does Seattle have a weekend weather curse?

With rain, clouds, and cool temperatures on Saturday and Sunday, followed by increasing warmth and sun when we are stuck inside for work or school?

 Let us investigate this terrifying possibility by examining the conditions this spring.

I  began by looking at the high temperatures at Seattle-Tacoma Airport for March, April, and the first 15 days of May.   The results are found below:

Average Weekday High Temperature:    60.4 F
Average Weekend High Temperature:    57.4 F

MY GOD, it's true.  High temperatures have been 3F greater during the week.   Highly significant difference.

My calculator shaking, I found the average amount of precipitation per day during the same period:

Average Daily Precipitation During Weekends:  .35 inches
Average Daily Precipitation During  Weekdays:  .16 inches

This is scary.  More than twice the amount of rainfall per day during the weekends than during weekdays.

I have heard that some folks blame this anomaly on Global Warming. That greater combustion of fossil fuels during weekdays is warming the air both directly and through excessive greenhouse gases.  Or that combustion particles are somehow interfering with natural weather processes.   You can expect headlines in local newspapers and web media when they learn of these ideas.  Particularly one local newspaper.

But the truth is that the origin of this anomaly is beyond science.  Beyond logic.  It is the Godzilla of weather.

Perhaps we have been cursed.  Perhaps we are being punished for some communal sin.

But in any case, my colleagues and I must look for the meteorological silver bullet to end this blight on our communal happiness.

Saturday Update!!

Turns out that Scott Sistek of KOMO TV took my analysis one step further and confirmed the results today in his own blog (found here).  For example, after adding January and February 2014 he found that Saturday was the wettest day of the year.  And going back to 1949 he got the same results!  Don't ask me whether these results are statistically significant, I don't want to get into that.  This is metaphysics not physics.


  1. When one is retired it does not matter. I am tickled pink about this May. OK, sunburned pink...

  2. I have to admit, I think it's just random. It seems that a lot of our weather patterns take about a week to push through... so if we get a rainy weekend, then the pattern plays out (rain for a day or two, high pressure building in and drying us out), then another front comes across and it rains again. If we got a "quick" front, it might rain Thurs/Fri, and then we'd have a dry weekend and might have a series of them.

    In short, I think you must be joking, Cliff, because this seems to be a strong case of perception bias... people noticing what they want to notice but ignoring data that contradicts.

  3. What sayeth your calculator about the significance of a 'control' weekend made up of any, (and preferably all), other pair of consecutive weekdays?

  4. One should expect greater statistical variability over smaller sample sizes, e.g., weekends in comparison to weekdays. Does the observed pattern bear out over many years? How often does the converse pattern hold?

  5. Cliff, thanks for the chortle this morning.

  6. Oh, man, some folks may need to consider having their humor detector recalibrated.

  7. Wow, Cliff just trolled all of us... Hilarious!

  8. This isn't just a funny story, but a real effect in some places. While Cliff's observations (and Scott Sistek's further analysis of the data) indicate that it might not be statistically significant for Seattle, it is a statistically significant effect on the east coast. An article to this effect was published in Nature in 1998:

  9. Skydivers across this country like to tell this joke: "Q: What do you call a bright, warm, windless sunny day? A: Monday!"

  10. What variables could be different between weekdays and weekends?

    How about traffic?

    Does the amount of traffic change enough to produce a different level of particulates in the air between weekdays and weekends, on average?

  11. I'm afraid we are just plain out of phase. It seems like the dry-to-wet-to-dry cycle is often about a week long in the spring. Unfortunately sometimes the wet part is in phase with the weekend. but it does seem uncanny, and it is easy to believe that the "weather gods" have a bad sense of humor... I don't really think the traffic or anything has a short term effect on the West coast. We just need a "short wave" to shift the cycle.

    Of course part of the problem is that the weekend has only two days out of seven.

  12. Hear, hear, Ansel. Have been thinking the same thing for a long time. If only we could just lose a few weekdays at a strategic time! Alas. Thanks for blogging about this, Cliff!


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

A Potent Atmospheric River Will Bring Heavy Rain and Some Flooding to the Northwest

If some folks thought that a strong El Nino would protect the region from heavy rain before the new year, they were mistaken. A substantial ...