Climate Matters: Blocking high pressure brings abnormal heat waves

You've likely been enjoying recent milder temperatures but these conditions are pretty extreme for this time of year. Highs this past week have soared 20 degrees above average; our low temperatures actually look more like our seasonal daily highs. This heat wave was fueled by a stubborn high pressure system reminiscent of more intense patterns of blocking.

A ridge of high pressure that formed over the continent recently was able to slow down the meandering jetstream, but not enough to reach official thresholds of what is known as blocking high pressure. When high pressure systems develop, they clear and dry out the area beneath and can persist in the same region for days. If high pressure officially lingers for 5 days it is a blocking event, and these patterns are slowly becoming a more common sight.

Dr. Anthony Lupo with the University of Missouri has studied these events extensively and says blocking would typically occur once per year over North America in past decades. However, into the 2020s these have skyrocketed with 4 events in 2023 alone. Dr. Lupo says this decade so far we have seen 11 blocking high pressures, while that would usually be the number observed over a full decade.

There isn't a clear connection between this increase in blocking and a change in climate, but Dr. Lupo and researchers at MU continue to investigate these patterns. One trend they've noticed is an increase in blocking during the springtime will typically bring a milder and wetter summer and vice versa. Unfortunately for this year ahead we are taking the other approach, with a relatively steady jetstream currently that could become more blocked by the warmer summer months.