Thursday, August 29, 2019

Unstable Sky

When I looked out this morning around 6:15 AM at the beautiful sunrise, I could see it.  The potential for showers and thunderstorms was there. 

Below are images from the Space Needle Pano cam at 6:10 and 6:20 AM.  Not only was the sunset beautiful, but the colors changed radically in ten minutes from red to yellow.

But look at the clouds.  There is a deck of mid-level clouds that are broken into lots of puffy, individual elements.   This is sign of instability--the tendency to convect--in the middle atmosphere.  And often precedes convection (e.g., thunderstorms) in our area.



And in fact, the 6:18 AM weather radar shows a line of showers moving northward over southern Washington (see below).    Olympia is feeling it as I write this.


There is convection--thunderstorms--embedded in this line, as shown by the lighting detection network.  For example, here are the lightning strikes (red and yellow crosses) during the 30 minutes ending 5 AM from the UW WWLLN network run by my colleague, Professor Robert Holzworth.  The background is the infrared satellite image at the same time.


This convection is associated with the lifting forced by an approaching upper level trough, which is invading the high pressure ridge that gave us the warm temperatures the past few days (see upper level map at 5AM below).  You see the (subtle) trough just off the NW coast?


Most of the showers should stay south of Seattle.  But today (Thursday) will be a major step down (from the upper 80s into the mid to upper 70s).   This weekend?  You may not want to ask.

The forecast of the upper level situation (500 hPa heights...roughly 18,000 ft)  for 11 AM Saturday shows a strong trough approaching our region. A trough that brings upward motion, clouds, and rain


In fact, the forecast 24h precipitation ending 5 AM Sunday, shows.....well....some rain. Saturday will be mostly cloudy with highs in the lower 70s.  Plan accordingly.  


This weather pattern is typical of what we have seen all summer:  normal variability and precipitation, going between warm and cloud/wet spells.   And what has prevented the anomalous wildfires/smoke of the past two summers.

8 comments:

  1. You hit another home run, Cliff. Here in Olympia we saw lightning at about 4:00 am, then light rain at about 6:30. It's still raining at 10:00.

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  2. I started hearing rumblings about 5:30 in Olympia. At first I thought it was Fort Lewis but then I started seeing the flashes from the lightening as it got closer. Opted to drive to work rather than ride my bike and saw some lightening strikes along the way. I was glad I was in my car.

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  3. Big flashes and boomers in Portland, beginning before 3AM. Just a sprinkling of rain.

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  4. Cliff, long time blog reader and admirer here.
    A question for you or others on this blog.
    At the end of the post you state that last summer’s wildfires/smoke were anomalous. But in your last years blog post you talked about how smoky summers were sort of normal for Seattle area a century ago because our summers are supposed to be dry and hot. You even mentioned that Mark Twain wrote about a smoky Seattle summer when he visited here in 1895. My takeaway from your blog was that smoky Seattle summers were a normal until Forest Services began suppressing fires and in a way the past few smoky summers were a return to the old normal. Is that not correct?

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  5. Cliff, am going sailing down the west coast starting this weekend. Do you have any suggestions on websites that give decent off-shore weather reports?

    I've got a few I use already, but was curious if you had any you preferred. Thanks!

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  6. I've lived in the Puget Sound basin my whole life, and this is the best summer I've seen in years. Reminds me of my childhood. I can only dream that we might have more like this.

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  7. A lot more rain, thunder and lightning than they were predicting down here in SW Washington. The thunder was shaking the house like sonic booms.

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  8. Not much action on the King-Snohomish line... supposedly the convergence zone. Phooey!!

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