September 01, 2017

Drizzle Storm Causes Power Outages in Seattle

Earlier in the summer, a highly experienced and currently retired Seattle City Light manager (Dana Wheelock) forecast some power outages when the rains returned to Seattle.

I was surprised, but he explained that a long, dry summer sets things up.  All kinds of particles get deposited on insulators (from smoke, dust, pollen, etc.) and they don't conduct while dry.  But add some light rain and the muck can provide an electrical path---causing shorts and even electrical pole fires.

So when it started raining over north Seattle yesterday morning, after a very dry summer, I mused to myself about what Dana said.  And then it happened... the power started flickering in my house... and later when I checked the Seattle City Light outage of page...lo and behold, there were a number of outages in the area that got hit by rain.  Dana knew what he was talking about!

Now let me be honest... the rain was not well forecast.  It was not in the National Weather Service Forecast the day before and the UW WRF model had only some light precipitation that was 3 hours too early (but in roughly the correct location).

The Camano Island weather radar barely got a handle on this very shallow precipitation band, which was associated with a transient line of convergence in the lee of the Olympics Mountains (a degenerate form of the Puget Sound convergence zone).

Here is a radar image for 11:09 AM that shows the band of precipitation stretching from Seattle to Bellevue.

The physics of this rain is interesting:  it was a warm-rain event in shallow stratus clouds.  No ice involved.   Lots of small droplets.  That is why I call it a drizzle-storm.   But that drizzle added up...about .2 inches in North Seattle over a few hours.

Fortunately, the rain missed Seattle-Tacoma Airport, allowing us to tie the all-time record low precipitation record for July-August (.02 inches) at that location.

And talking of records, we just beat the all-time record for number of consecutive days about 70F.  The record was 61 and we are now at 64.

The weekend?   A big ridge of high pressure builds over us and temperatures will zoom in the mid-80s Sat/Sun and then to near 90F on Tuesday.  No precipitation.

And yes...some smoke may come back as winds aloft turn easterly.  Sorry.


  1. Cliff, when will this damn heat finally end, & pivot in earnest into cool & comfortable Fall weather?

    1. It will only only get hotter every year with runaway warning. And despite Cliff's reassurances, the storms will only get worse every year.

  2. Such power outages may seem strange, but I'll bet I know why: Bird manure! Birds love to sit on power poles, and most times they only touch one side of the line so the birds themselves don't get hurt. When it rains frequently, the manure doesn't build up too much. But manure- guano in particular- contains salts, which are conductive when wet. When a whole summer's worth of droppings get wet... Pow!

    Dead branches crossing both lines might also cause trouble when it rains.

  3. Was a welcome event yesterday. It was enough that the water was running downhill on the roads here near 80th NE/Lake City Way.

  4. "It was not in the National Weather Service Forecast the day before and the UW WRF model had only some light precipitation that was 3 hours too early (but in roughly the correct location)."

    But we can assure you that we can predict sea levels in the sound for the year 2100!

  5. We received .01" just west of KSEA.

    Must have just missed them!

  6. "But we can assure you that we can predict sea levels in the sound for the year 2100!"

    We can both confidently predict that there will be more traffic in Seattle in 10 years, but neither of us can predict if a blue car will pass in front of your house in precisely 5 minutes. Predictable "Climate" (and related effects) versus small-scale "weather".

    At least today (Friday) we can both predict that if a car appears in 5 minutes, it won't be wet from rain.

  7. When I worked in oilfields in North Africa they would clean off the insulators with jets of distilled water. There wasn't much rain but ocean spray would short them out over time. Not a popular job.

  8. Going through rain withdrawals here in Northwest Washington. Would have earnestly thought about driving to see it actually rain in North Seattle, had I known ahead of time. Seriously, I'm done with hot and dry. What is you take on this winter. Enso neutral means we have an even chance of snow in the lowlands? NWS shows almost all the continental US above average temps for SON and OND.

  9. But really major drizzle looks like...

  10. When in July did the rain stop to start the rain less record?

    It's Sept. 3 now without rain for many days.

    With the exception of .002 in. July, how many days have we gone without rain?

  11. Harvey intensified rapidly amid sea surface temperatures in the Gulf of Mexico up to 2.7 - 7.2°F (1.5 - 4°C) above average, relative to a 1961-1990 baseline, according to NOAA. Who is right?


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

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