November 29, 2015

Dangerous Black Ice, Fog, and Super-inversion

It's dangerous out there Sunday morning...seriously.

The past few nights we have had increasing ice on our roadways, particularly on the side streets, as frost developed during the evening.

Why frost?  Because ground temperatures are cooling to freezing due to excellent conditions for radiational cooling to space (clear skies, light winds, long nights, relatively moist lower atmosphere from previous rains).

And today something is making it much worse: dense fog, which can cause substantially more roadway icing as the water droplets in the fog freeze on to cold roads.      Here is the view in my neighborhood in NE Seattle:

You can view roadway temperatures on the Seattle SnowWatch site, developed by he UW and the city.  Here is the latest at 8:15 AM (roadway temps are in the boxes).  Freezing (32F) on the University Bridge and one of the West Seattle spans.  Others very close.

As noted in my previous blog, strong and persistent high pressure produces strong inversions around here, particularly in areas within basins and valleys (e.g., Puget Sound, Columbia Basin, river basins), with cold air pooling at lower elevations.   Let me show you the very strong inversion over Seattle Sunday AM (see plot with vertical temperature profiles over NE Seattle between 10 PM Sat to 4 AM Sunday).  An increase of 10C (18F) from sea level to 800 meters above the surface.

With an inversion over us, it was actually warmer at higher elevations yesterday.   Here are the max temperatures on Saturday.  Mid-50s in the mountains, but low forties around the Sound and NW Washington.   Mid-30s around Olympia.

Why so low near Olympia?  Because fog held in all day there (see satellite image on Saturday afternoon)

Today, low fog is extensive over Puget Sound and eastern WA is all fogged in.  The great irony of eastern Washington:  so sunny during the warm part of the year, but a fog bowl during mid-winter, particularly when high pressure is around.

You want to get warmer and see sun?....take a hike to the top of a local peak or head to one of the higher hills east of Seattle.  Here is an photo from Peter Benda, who lives at around 1000 ft on the Eastside.  Nice and sunny up there.

Sick of cold air, fog, and lack of rain?...don't worry.  Everything changes on Monday as we switch back to clouds, warmer temps, and rain.  Normality.


And don't forget saving our local radio station KPLU.  As I described in previous blogs, we can save KPLU if listeners will tell UW to stop the acquisition and give KPLU a chance to purchase its freedom from PLU.  Why should UW kill a popular local public radio station?


  1. I saw some of this yesterday when my son and I drove up to Denny Creek. It was worse on the freeways than in town, from what we saw. One car spun the wrong way in I-90 in Bellevue. A minute or two later, we hit a patch of ice but the loss of control was momentary. Then we saw two cars on opposite sides of the eastbound that looked like they had met by accident. I'm just glad the side winds were not along the same stretch or it would have been ugly. Still icy in the shaded parts when we came back mid-afternoon.

  2. Thank heaven it's changing finally; today is FREEZING COLD - hopefully the last of this rainless, cold stretch.

  3. Tell me about, I road my bike from Shoreline to Snohomish today. I was cussing myself all the way there.

  4. A couple runners at the marathon fell on the icy express lanes - I slid a good three feet myself.

  5. "Just saying it is scary.
    Black ice just sneaks up on you. Robbing you of gravity!"

  6. Hi Cliff,
    There is a low forming off of Oregon. Where is it going and will it bring wind?

  7. Cliff,

    I am interested to learn how much of this inversion was forecast and the subsequent data available to cities and WSDOT prior to the weekend r.e Black Ice issues? I ask this because there was a complete lack of preparation.

    This morning I saw 3 vehicles spun off into ditches on I-90 E at the Issaquah Exit as the entire roadway was untreated. Later this evening the sidewalks in Redmond became a sheet of ice, no salting, nothing proactive at all. Not sure how the elderly or disable are supposed to manage, the city doesn't care that is for certain.

    In contrast I drove to Cle Elum today and upon each curve in the road there exists a mass of salt and grit to aid in traction, sidewalks are sanded, clearly someone is thinking East of the crest. In all seriousness there is no excuse and city leaders must be held accountable for their lack of preparation if this data was available to them.

    I am certain that many injuries and even a death could have perhaps been prevented this weekend. It doesn't take a rocket scientist to know that untreated roads and sidewalks result in serious accidents.

  8. When I was a young lad in Walla Walla I do not remember the long duration of foggy days we now experience. Lakes have been created on the Columbia & Snake Rivers in my lifetime. My father remembered, when a boy, in late season when their flow was much reduced. I think its foggier more winters now than six decades ago but I've no data.

    Have these lakes changed local conditions in Eastern Washington?


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