The End of Smoke, the First Rain, and Cooler Temperatures Return: But Are There Dangers with this Change?

We are about to experience a major shift in our weather, one that will end the above-normal temperatures, bring the first real rain of summer, and push the smoke away from western Washington.  Normal conditions will return.

But as we will see, there are some dangers to this change, including pole fires, power outages, more wildfires, and slippery roads.

During the past week, a ridge of high pressure has dominated the flow over our region, as shown by this upper level chart for Tuesday at 5 PM.  It has been a very stable pattern, resulting in warm conditions and light winds.  The smoke settled in over our region.

But the models are emphatic that the ridge will move inland, and a Pacific trough will approch us.  The forecast map for Saturday at 5 PM shows you what I mean.

Today (Friday) will be the last warm day before the change, with temperatures rising into the lower 80s.

But Saturday will be a different story, with increasing clouds and wind from the approaching disturbance.  The smoke will be pushed eastward.  And even some light showers are possible.    The major rain will wait until Saturday night and Sunday morning.

Here are the 24-h total precipitation forecasts for next few days.  For the 24 h ending 5 PM Saturday, light showers over western WA and what looks like some convective (thunderstorm) precipitation over eastern Oregon.  It is good the eclipse is not tomorrow!

But the next 24 hr (ending 5 PM Sunday) is much wetter over western WA and the coast.  No much by winter standards,  but the most we have seen for months (roughly .1 inches over the interior and .5 inches along the coast)

Now what are the potential downsides to this change of weather?

1.  Slippery roads.  The first rain of the late summer falls on roads that have accumulated oil, dust, and other particles, often producing a transient slippery surface.  So drive carefully when the rain starts.

2.  Pole fires and power outages.   According to a retired City Light employee I have worked with, the dust and muck deposited on wooden power poles can become conductive with a little rain, causing short-circuits, fires, and power outages.  The long period without rain this summer makes us particularly vulnerable.

3.  Lightning.   The approaching trough can initiate thunderstorms that could start new wildfires over the Cascades and eastern WA/Oregon.  And yes, perhaps endangering a few golfers.

I suspect most of you will be happy with the return of normal weather.  

Many are starting to think about the eclipse.   Well, the latest upper level (500 hPa)  forecast from the National Weather Service GFS model for 11 AM Monday morning (21 August) shows a trough, with clouds and showers, over the region...not good!   But don't worry.... the skill at 10-11 days is very poor.

from Cliff Mass Weather and Climate Blog http://ift.tt/2vq5TNR