WHAT'S CAUSING THE EXTRAORDINARY TEMPERATURES IN THE PACIFIC NORTHWEST?

 

Since I'm from Seattle, I've been intrigued by the historically high temperatures there.  Today, in Maple Valley, Washington, SE of Seattle, where my grandfather built a home and family still resides, it was 109F today, 37 degrees ABOVE the normal high.

Lytton, British Columbia, 231 miles north of Seattle on the Trans-Canada Highway, recorded a high temperature today of 46.6C or 115.88F.  

Since the majority of homes in the Pacific Northwest do not have air conditioning and the normal high temperature in Seattle on June 28 is 72F, it's not difficult to imagine the stress for senior citizens and others this historic heat wave has become.

The explanation is a "heat dome," the most intense on record, illustrated above.

A heat dome is a essentially a mountain of warm air built into a very wavy jet stream, with extreme undulations. When the jet stream — a band of strong wind in the upper levels of the atmosphere — becomes very wavy and elongated, pressure systems can pinch off and become stalled or stuck in places they typically would not be. 

In this case, a ridge of high pressure, which is the heat dome, has become lodged in the Pacific Northwest. It is acting as a block in the atmosphere, not allowing the weather to move. The specific type of block is called an Omega block, because it looks like the Greek letter Omega, and the hot air is pooling inside.