Extraordinary Weather Pattern Creates Record-Shattering Heat

MONROE, La. (KNOE) - People throughout much of the western United States and Canada are dealing with extreme heat. But this is not just any ordinary heat wave. In some locations, recent high temperatures have set all-time records.

Portland, Oregon is one such location. This city’s average high in late June stands in the upper 70s. According to the National Weather Service (NWS), however, the city hit a sizzling high of 112 F on Sunday, June 27. That reading is an all-time record high temperature for the city. Records go back to the early 1940s.

Another large city dealing with the unprecedented heat is Seattle, Washington. Known for its cloudy skies and rainy weather, the city’s average high on June 27th is just 73 F. But on Sunday, June 27, the city saw the mercury soar to an eye-popping 104 F. This broke the old record of 103 F set back in 2009. It also represented an all-time record high, and records in Seattle go back to the year 1894.

Quite simply, nobody alive today has seen weather this scorching in the Pacific Northwest. Events across the region have been cancelled on account of the dangerous heat, and power grids are strained by overwhelming demand.

So where is this unprecedented heat wave coming from? Why is it occurring?

The answer lies in a fairly common meteorological phenomena known as a ridge.

Ridges are most frequently seen during the summer months in the US, though they can also occur during winter as well. A ridge is formed when a large area of high pressure causes the jet stream - a fast-moving current of air in the upper atmosphere - to “bend” into a bubble or arch-like shape. Jet streams often serve as dividers between air masses, so the cooler air north of the jet stream is forced far away when a ridge forms.

The high pressure systems that create ridges also typically sit over the same areas for days on end. Each day, the sun causes the air to become just a little hotter than it was the day before. When we have heat waves during the summer, it’s usually because a ridge is at play. That is why ridges are also commonly referred to as “heat domes.” These can create some truly impressive high temperatures, especially in the western United States.

In other words, this type of weather pattern is not abnormal. But the effects of this particular heat dome - the all-time record highs and sheer intensity of the heat wave - are abnormal. Scientists chalk this up to ongoing climate change. A similarly-unprecedented heat wave has been occurring in Siberia the past couple of weeks, and satellites measured a surface temperature of 118 F north of the Arctic Circle. These are never-before-seen readings.

Back closer to home, the same ridge created by the high pressure system caused the jet stream to bend far north into Canada. That set the stage for the extraordinary heat in the Pacific Northwest and Canada.

The jet stream then plunged back down into the central United States on the eastern edge of the ridge, creating several days of intense rainfall and extreme flooding across the Midwest. Some towns in Missouri received well over 10 inches of rain in just a few days.

The heat wave generating pattern shows definite signs of breaking down and moving on over the next few days, but the effects have been felt clearly enough to make their mark on history.