If you have been watching the weather forecast lately, you have heard us talk a lot about the temperature inversion that has been in place over Western Washington.  A temperature inversion occurs when a warmer layer of air sits above colder air at the surface.  Instead of the air cooling off with height like it usually does, under an inversion it actually warms up with height.  While temperatures have been stuck in the 30s around Seattle, the mountains have seen highs in the 50 and 60s the past several days!  

That warmer air acts as a lid, trapping the fog and pollutants near the surface.  That is why it has been so gray around Puget Sound.  The other thing this inversion did was create an amazing optical effect… a superior mirage. 

Check out the video Chopper 7 captured Tuesday morning.  A special thanks to KIRO 7 Photographer Scott Crueger for shooting this amazing video!  The first part was shot over Marysville looking north toward Galbraith Peak in Whatcom County.  The second part of the video is shooting toward the Issaquah Alps.  It almost looks like the mountains are growing.  In some of the video it almost looks like smoke is spewing out of the mountain tops.  Yes, we live around active volcanoes, but there is no eruption taking place here. 

What you are seeing in this video is a superior mirage; an optical effect that makes objects appear taller than they normally are.  With the temperature inversion in place, that warmer air aloft is a lot less dense than the cooler air toward the ground.  Light waves move slower through that colder air and faster through the warmer air aloft.  With this change in speed, the light waves bend, making the objects appear higher in the sky than they really are. 

We won’t be seeing any other mirages like this over the coming days.  The inversion is mixing out as rain returns to Western Washington on Wednesday.   

Have a great day!  

-Sam Argier, KIRO 7 Meteorologist