Friday, December 20, 2019

The Darkest Day in Seattle History

Today we broke an amazing record--it was the darkest day on record here in Seattle.

Or to be more exact, the darkest day ever observed at the University of Washington during the twenty years we have recorded solar radiation on the roof of the atmospheric sciences building.

3PM in Seattle from the Space Needle PanoCam

Over the entire day, we received .37 million Joules of solar radiation over a square meter surface.  The old record low was .39 on December 14, 2006 ( a joule is a unit of energy).  The runner up was .44 on December 7, 2015.   To give you some perspective, in July of this year we had several days reaching 27.

Solar radiation on the top of my department roof for the last three days.

Consistent with the UW measurement, here is the solar radiation at the Washington State University AgWeather site in Seattle:  December 20th was the lowest over the past year.


Everything had to be perfect to achieve this depressing record.  First, the date.  The winter solstice is tomorrow, so solar radiation reaching our atmosphere is about as low as it can be.

And then we had a strong atmospheric river, with multi-level cloud decks and loads of precipitation parked over us all day (see MODIS image below). Clouds and precipitation scatter solar radiation back to space (that is why the clouds look white in a satellite image).


Today is as bad as it gets around here, when it comes to darkness and gloom.  You may not see a similarly bad day for the rest of your life if you stay here.  But you probably won't (stay here).

I understand that crowds of visiting and expatriate Californians are rushing to Sea-Tac Airport to get back to sun before it is too late.

Picture at Sea-Tac courtesy of KPLZ

23 comments:

  1. Excellent practice for when global climate change forces us to be come a nocturnal species (go Morlocks!)

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    1. that won't work when it's 135 in daylight and 100 at night, looming as 150 billion gigatons of methane released across the Arctic circle cause temps to rise 10 C and spread south from there to the equator, also ending agriculture in the northern hemisphere. no large mammal (us!) can live long in those conditions.

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  2. Okay my weather station does Watts per meter squared. It reported 68 w/m2 peak for the day. In the summer I get almost a thousand w/m2. I'm in Moses lake. Ya it was dark!

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    1. Thanks Jeff I had to come to Cliff's blog to see that his number is TOTAL Joules/m2 for the day. I'm used to w/m2 also.

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  3. If it weren't for Christmas lights and cheer...it'd be horribly depressing. :P

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  4. This is the weather I miss from my childhood. :)

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  5. Yep... You are a fun squasher Cliff... Do we need reminders? And it's still dark here at 7:42pm tonight.... :) Just like at 1:45 this afternoon... At least we are saving wear and tear on our light switches.... They stayed on all day.... :)

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  6. Noticed
    1) The street lights were lit on the ship canal bridge at 11am.
    2) The solar powered speed limit signs did not work
    3) Sun glasses made it look like some sort of storm chaser show.

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    1. Is THAT what was wrong with the speed limit signs? I saw some displaying random numbers when everyone coming toward them was stopped at a light.

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  7. There is one place darker.
    That is the cave in which I am about to crawl back into and go back to hibernating

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  8. Family traveling from Tri Cities to Bellevue yesterday... it was 63* over there! Hope there’s a pause for the cause: Snowflake Lane.!❄️🎄 but family’s together; who cares. Merry

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  9. I've been reading your blog since your article on needed NWS improvements appeared in The NYTimes several years ago. Your blog is truly a contribution to the general public's understanding of weather and the environment. Thank you! This particular post is a good reminder of those things the PV salespeople generally fail to mention . . .. Yes, you do need a back-up source of energy, at least in the higher latitudes in the winter.

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  10. Joules who? Joules Verne? Watt are you talk'in about? I don't give a femto-erg!!

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  11. I started as a grad student in atmospheric sciences at the UW in 1993, and the department was measuring solar radiation on the roof of its building then. Was the technology improved/deemed official in 1999?

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  12. I'm disappointed I missed all the rain, being indoors without windows all day working.

    On a good day, a solar panel in Western Washington will generate about 6 kW hours of electricity per kW of rated capacity. On a year round average, it should be 3-4 kW hours.

    0.37 MJ is barely over 0.1 kW hours.

    Put another way, panels that cost $2000-3000 to buy and install would have only made 1 cent worth of electricity yesterday.

    This is the extreme case, but it illustrates why Dr Mass recently opined that we can't expect solar power alone to solve our energy needs. Even efficient heat pumps still need a significant amount of power to keep our homes warm, and across much of the country, that power is not easily available from the sun in the winter. We need a mix of sources, concentrated where they work best.

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  13. And my roof-top 6 kWh solar array near Sand Point, Seattle produced 0.33 kWh yesterday and 1.06 kWh today, Saturday, Dec 21. I missed the bright parts today.

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  14. At one point in the late morning, it got amazingly dark. It was quite nice!

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  15. Cliff,

    This is a fun blog. It's bringing out people's sense of humor.

    Shocking the darkest day record is broken. I'm always excited about the days starting to be longer.

    I can't wait to read what you come up with next!

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  16. Here is a fun idea, its the solar orbit brightness equivalency index. The index is:how away from the sun would you have to be to experience brightness equivalent to where you are on earth now? You could never be closer than earth orbit. But whats a cloudy day in Seattle? Mars? The asteroid belt? Jupiter? I did quick math once and figured that plutos orbit is about as bright as 900 full moons. Is would be a fun of your daily forecast

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  17. In Dec 2018 Craig Mass wrote: "The sun is naturally weaker and shorter-appearing due to the time of the year. And its feeble rays are usually further weakened by considerable cloud cover, as Pacific weather systems reach our region."
    Beside the increasing transient cloud cover, and the path through the sky, is there another factor that leads you to say the sun is "naturally weaker" in winter? In particular, if you took a cloudless sunrise in summer and compared it to a cloudless sunrise in winter, would there be any difference in the intensity of the sun?

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