January 11, 2016

Super Icy

I normally bike to work every day, rain or shine.  But not today.
When I went outside to walk my dog, I started to slide.  Later when I tried to drive my car to the UW, it started to slide and the traction warning went on.

The ground was really iced up in places right now and there are two possibilities of the origin:  freezing rain and cold rain on a freezing surface.

Right now the National Weather Service has a freezing rain advisory out for the south Sound and around Puget Sound away from the water:

Freezing rain occurs when rain falls from an above-freezing layer into a surface layer that is cold enough to supercool the rain to below freezing.  When it hits a cold ground the rain freezes immediately you can get freezing rain.   But according the temperature observations above Seattle (see below), there is no real evidence of much as subfreezing layer above the surface.

There may have been more of a cold air layer at low levels over the south Sound and along the eastern slopes, so classic freezing rain might have occurred there.

But I think it is a bit more complicated that just freezing rain.  I  suspect what has occurred in many locations (like Seattle) is that with clear skies last night, the surface cooled to below freezing (see min temps below).  Then cold rain came in this morning and froze on the cold surface.

So be careful for a few hours until the ground warms up.

Update:  there were a number of bicycle accidents this morning on Seattle's Burke Gilman trail due to icy conditions.


  1. I am down in Tacoma and biked in to work. When I left it was clear with a frost layer on the road but not too bad. About halfway through the commute it started to rain and within minutes it was very icy slick. I think I beat the worst of it but it was surprising how quickly the roads iced up.

  2. At 8:20 this morning in East Bellevue, the car's thermometer reported 30F; the SchoolNet professional setup at Phantom Lake Elementary 0.8 miles away reported the same. My car was coated in slushy frozen stuff, and more definitely came down for a little bit as the windshield wipers made little piles of slush from cleaning the glass. By 8:40, it had switched over to just rain, but before that, it was cold enough that it was freezing at the surface. I thought it was supposed to be dry all week? If it's going to be so cold, I would prefer that it stay dry instead of turning icy!

  3. I skipped riding from Bellevue to Seattle all last week due to the black ice on the trail and parts of the road. This morning I was thinking about riding but the clear sky, and the thick layer of frost on my car made me think that the Mercer Slough would be just as icy this morning as it was all last week.

    A week or two off in the winter for ice beats the multi weeks off due to an injury.

  4. what happened to the dry here, and wet in southern california? what shifted?

  5. I've been commuting by motorcycle for ten years, from Green Lake to downtown via I-5. Usually I don't worry about rain. Subfreezing pavement is often dry. Wet pavement isn't usually frozen. This morning I headed out as light rain began. In a couple of spots in residential neighborhoods my rear tire slipped out a little. It was surprising and unnerving, so I took care. No worries about I-5, though. Rush hour traffic puts a lot of energy into the pavement. My guess was that the rain froze as it hit subfreezing ground in low traffic areas. I did not see evidence of superchilled rain freezing as it hit other surfaces, like my face shield. Out of about 5,000 commute trips this was a first. I hope no one got badly injured on their bicycles.

  6. Riding by bike in Redmond this morning about 7:30 the rain was falling as tiny ice pellets. The pavement was relatively dry. Last week was very sketchy with icy spots even near water where you'd expect warmer temps. The new sidewalk areas with the pea gravel concrete by the Husky Stadium light rail pedestrian flyover was especially slick.

  7. I was wondering why I slipped on the sidewalk this morning (thankfully didn't fall down) and hadn't slipped at all during the rain in December - this explains it. Thanks.

  8. I'm on Bainbridge Island and had heard the first showers of rain fall on the master bathroom skylight in the wee hours of the morning, so I assumed when I got up at 7:00 it would definitely be above freezing.

    Imagine my surprise to see that everything was still frosty as another wave of showers was coming in. The private side street I live on quickly acquired some very icy spots. Thankfully it was patchy and easy to avoid. I definitely took it slow on my way to the ferry. Icy and wet can be tough to tell apart sometimes.

  9. The Basin woke up to this as well. Waterville Schools were cancelled, so I dont know how bad it was on the plateau.

    I do know Quincy was really slippery. I fell twice on my front walk. I slid while driving 5mph on my street. I watched kids walking to the bus stop fall down. I suggested they walk in the snow covered yard edges.

    It was not a fun morning.

  10. My crash on the Burke yesterday affirms your idea that surfaces froze the rain. The asphalt and concrete were mostly fine but the new brick pavers at Montlake and Pacific by the stadium were an ice rink. Those bricks are a commuter hazard!


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