December 12, 2018

Seattle's Darkest Day in Three Years

Here in Seattle it was extraordinarily dark yesterday.  The darkest day in years.

The total radiation on Tuesday on top of the roof of the atmospheric sciences building was .54 Megajoules (MJ) per meter squared (a joule is a unit of energy).

To give you some perspective, here is a table of the lowest daily radiation amounts since 2004 at the UW, provided by UW Research Meteorologist Mark Albright.  The date of lowest radiation is also noted.  As you can see, yesterday was the darkest since 2015, where the total dropped to .44 MJ per meter squared on December 7th.

  Year           Date        Amount of solar radiation
 2004  1229  0.64 MJ/m**2
 2005  1201  0.61
 2006  1214  0.39
 2007  1202  0.51
 2008  1225  0.79
 2009  1215  0.74
 2010  1223  0.57
 2011  1210  0.68
 2012  1219  0.48
 2013  1220  0.56
 2014  1210  0.55
 2015  1207  0.44
 2016  1219  0.68
 2017  1218  0.69
*2018  1211  0.54

The absolute worst was the obscene value of .39 on December 14, 2006.  On a day like that, you might as well stay in bed.

You will note that the darkest days are all in December, running from December 2 to December 29th.  

So why was yesterday so dark and why are December's the month of most feeble solar radiation reaching the surface?

Two things are happening.  First, a lot of deep clouds, which prevent solar radiation from getting to the surface, and second, this is the period of short days and low sun angle.

The visible satellite image at 2 PM Tuesday indicated a dense frontal cloud band right over western Washington (see below)

And the infrared image at the same time shows that the cloud tops were very high, and thus the clouds were deep.

To make it all worse, the sunrise/sunset table for Seattle shows that we are now experiencing the earliest sunset of the year (4:17 PM).  The day will continue to get shorter until December 21st.

But there is something very positive happening lately:  lots of snow has been falling in the Cascades, with all the ski areas operating this week, although not all the runs are open.    And today (Wednesday) should be a much brighter day, with some intermittent showers.


  1. This comment has been removed by the author.

  2. "The absolute worst was the obscene value of .39 on December 14, 2006. On a day like that, you might as well stay in bed."

    Probably safer to stay in bed that day. It was pretty windy outside!

  3. How does this value compare to the amount of sunlight we get in June? Do you have a graph of the average monthly values?

  4. Cliff - where did you get the sunrise/sunset/day length table? My father in law, a retired statistician, created one for me for Sisters, Oregon, and I'd love to compare it to the one you're using. Thx, Robert

  5. Not surprising. My wife and I were walking around turning all the lights on in the house in the middle of the day, which even with them on seemed gloomier than usual. The house feels bright at night with that many lights on, but there was just enough light outside to seemingly suck their energy away.

    Even my three dogs seemed to pick up on it. They didn't want to go out more than necessary, even when it wasn't raining, and just laid around sleeping all day.

    That seemed like such an appropriate way to deal with such a dark December day that I joined them.

  6. I measured a maximum irradiance of 25 W/m2 at 1220PM yesterday 1.5 mi SW of KBLI which is the lowest maximum daily value that I can remember measuring since installing my solar sensor in summer 2016.

  7. I blame AGW and call for an immediate and inviolable tax on all organisms currently residing in the US, both living and dead.

  8. Cliff, I count on days like yesterday to get under the skin of a portion of our recent transplants. If the rain doesn't make them go back to the sunnier climes they came from, maybe the darkness will.

    Embrace the darkness! May the Sun disappear entirely for the next month.

  9. December 14 2006 was the day the Hannukah Eve storm hit. Any correlation?

  10. Dan, the only thing that would really work in that manner is if the PNW had a real, honest to goodness winter. Meaning subzero temps, ice a foot thick and huge amounts of snow.

  11. Sad to read Cliff is getting slandered and bullied under the guise of microaggression.

  12. The recent very personal attacks at the University of Washington against Cliff follow the same structure as the frenzy of phony microaggression slights has emerged in our society.

  13. @Robaire:
    Sunsrise / Sunset Tables (by location) for an entire year are available from the Naval Observatory site linked here:

    You need to calculate your own Length of Day if using these.

  14. Before we continue to mope and feel sorry for ourselves it would be interesting to compare our values to other US cities and other cities in Washington state. Anyone know how to find this data? Thanks

  15. Meaning the day of a named (colloquially) storm correlating with the lowest value for solar energy during that calendar year? Probably not...

  16. This was a fascinating post. Thank you! I learned something new today.

  17. Here is Emily Becker's latest ENSO update...... always interesting:

  18. A winters day, in a deep and dark December...

  19. codetalker - Thank you for posting that link.

    I urge everyone on this comment section to read it. Critically important. Here is the link again -

    How anyone can justify this is beyond me. The UW needs to take action immediately.

  20. It was sunny in Port Townsend and no rain...

  21. Well that explains it. It was miserable out there.

    HT to Codetalker for the link. Science is hard, which explains why there are so few scientists among us. Keep up the good work, Cliff

  22. Cliff, I am surprised you didn't correlate the lowest reading with....Hanukkah Eve windstorm of 2006 just for historical perspective.


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

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