Here at sea level, we are immersed in a puddle of cold air whose temperature is right at freezing. More, there is a naggingly persistent heavy fog, which is freezing on the roads to black ice. Just plain nasty.
Yet just climb up a little and the sun is out, and it is warm! The high temperatures yesterday in the Olympic range were in the 50's, with one reading of 64°! In fact the puddle of cold air is so shallow that you can take an elevator to get above it!
For the full low-down on this, I'll refer you to our famous local weather blogger, Cliff Mass. He has made several posts about this phenomenon.