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.
And yes...some smoke may come back as winds aloft turn easterly. Sorry.
from Cliff Mass Weather and Climate Blog http://ift.tt/2iNhRNe
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