December 24, 2010

Darkest Day and Possible Snow

This will be a blog about contradictions. Yesterday was very dark over much of the NW, in fact in Seattle it was the darkest day since January 10th of this year based on the solar radiation measurements at the UW (this fact was communicated by Mark Albright, past state climatologist). First, we start with the darkest period of the year based on the amount of solar radiation reaching the top of the atmosphere (of course, the darkest day by that aspect is December 21st). Then we add unusually thick clouds with lots of water content that scatter and absorb the radiation we do get. Between the two, not much got in. Here is the plot of observations and solar radiation at the UW for the last three days...the last line is solar radiation.....pretty pathetic yesterday!So how do we brighten things up? Snow, of course. And the latest runs are suggesting the potential for lowland snow next Wednesday. Here is the forecast for 10 AM next Wednesday: cold air in our vicinity and a low center off the SW coast of WA. This pattern, and the upper level flow associated with it, are close enough to the canonical pattern for lowland snow to be concerned. And the model explicitly is indicating snow near sea level. But I would not get too excited yet--this could change. But local municipalities should go into a watchful waiting mode, insuring that their crews are rested, the salt and deicer bins are full, and the reversible lanes of I5 are ready to go.

And I hope everyone has a relaxing holiday weekend.


  1. Today was dark too! I went to the store at around 2:00 pm and it seemed like it was was so dark and dreary! But you're right! Snow would brighten things up! Here's hoping it will...that would be great if it happened during Christmas break. Then the kids wouldn't have to miss any school! Any Merry Christmas to you too Cliff! Thanks for keeping us updated...even on Christmas Eve!

  2. Merry Christmas, Dr. Mass! Here's hoping to a white New Year. Thanks for the treasure trove of information you generously spend your time sharing with us amateur weather nerds.

  3. News from British scientists on the relationship between global warming and their changing winters:

  4. Really appreciate you showing a map that includes Oregon. A lot of us from Portland area follow you blog! Would really appreciate it if you showed at least the northern half of Oregon on maps more often. Thanks! John

  5. Cliff,
    Awesome blog. As an avid weather watcher, you are one of about 6 sources of info regarding weather that I check on a daily basis, I have to say I love your blog. So much so, I asked for your book for christmas and got it. Can't wait to dive in. May have missed my calling. May have to look into classes when I move back up to Seattle next summer. ***crossing fingers for lowland snow***

  6. I am an east coast transplant, working for a software company in the Seattle area. I like both your book and your blog. Both have been very helpful in learning about local weather. Thanks for taking the time to share! Happy Holidays!

  7. Yet another weak snowfall here east of the Cascades. But thank you La Nina, for providing a now rare white Christmas for us.

    Got a full day of sledding and snow shoeing with our Seattle relatives tomorrow. They're stoked.

  8. I have a personal thing called the "Sun Index" - that is, how many days I have gone without seeing the sun, even for a few fleeting moments. It has to be unobscured. A bright round disk in thin clouds or fog doesn't count.

    November and December hasn't been too bad so far, with the highest number being a 2. However, if I don't see any sun today, it will be at 3.

    It seems like a silly concept until the sun index gets up to 14 or 23 or higher which it does some years. Like the year not too long ago when there was measurable precipitation every day in November. And no sunlight.

    Thinking of blotting out the sun, here is a date to remember and put on your long term calendar. August 21, 2017. You will want to be somewhere along the latitude just south of Salem OR (preferably east of the Cascades in case there are clouds) that morning for a total eclipse of the sun. Totality begins around 10:15 and lasts just under 2 minutes. The last total eclipse seen in the Pacific NW was in 1979. The next total eclipse on the west coast after this one won't happen until 2045.


  9. I like to call the period from about Thanksgiving until the beginning of February "The Tunnel", obviously I refer to the amount of light. I've had your book for a while and now have visited your blog. I love the variety of the weather here (been here 40 years). Sunny weather every day is boring. You are a legend,


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