The Omega Block

Earth produced some unusual weather and atmospheric phenomena for the Midwest and Eastern United States during the middle and late spring of 2023.

As the temperatures rose with lengthening daylight, many people near The Mountains Are Calling headquarters in Central Ohio noticed something odd in the air. Though many Ohioans partake in the universal that is griping about the current local climate, largely people want more warm weather and less cold weather. Still, when summer hits in full force, the popular calls for autumn inevitably arrive. One reason for this disdain of the warmer temperatures for which they clamored is humidity. Summer days in the 80s or 90s are nice, but, if the humidity is too high, these days can become unbearable. Still, connotatively, the Midwest is viewed more as a cold spot than a warm one.

Yet, a quick look at the Köppen climate classification – a system used to divide the globe into climatic slivers – sketches a different image. Ohio (and much of the upper South and Midwest) falls either into the “humid subtropical” or “hot-summer humid continental” range or, perhaps, on the dividing line between the two. Subtropical? Many Midwestern eyebrows would raise at the fact.

Köppen–Geiger climate classification map - Nature Scientific Data

Go outside in the Midwest in deep summer and you will emerge into a hellscape resembling Florida or coastal Texas. So much water will fill the air that not only won’t you be able to sweat, but it will sweat into you.

This reality comes from two factors.

During the summer, weather patterns tend to line up such that moist air from the Gulf of Mexico streams northward into the Midwest. Further, in a process called evapotranspiration, water from the many crops grown throughout the region actually joins the wet air from the south. Some people dub this happening “corn sweats.” Corn, for example, can add 4,000 gallons of water to the air per day per acre!

For some, cornfields belong in horror films such as Children of the Corn. My corn terror takes a different form.

The wet movement has tangible consequences, beyond discomfort. The meeting of cooler air from Canada and warmer, wetter air from the Gulf helps to form Tornado Alley across the Midwest.

Just extend that red bar a little farther - graphic by Dan Craggs

July and August tend to be the worst for humidity, but one starts to feel it coming as spring progresses.

However, in 2023, the moisture stayed away through at least the beginning of June. People rejoiced as they found they could run or walk during the daylight hours without ejecting gallons of sweat. It was strange.

Just as this seemingly parallel dimension started to sink in, the smoke arrived.

Wildfire smoke in cities in early June 2023 - New York Times

Everyone started to notice fantastic sunsets. Some people posted photos of the sun “going down” while the sun was still well on its perch.

The culprit was a slew of wildfires all the way in Canada.

Huge swaths of the United States found themselves blanketed by thick smoke from our northern neighbors. So much for running in the non-humidity.

What was causing this haze to travel so far south and east? As it turns out, the humidity killer and the smoke bringer were the same meteorological phenomenon: an omega block.

An omega block - graphic from Fox Weather
The Greek letter omega

Typically, weather moves west to east in the United States, as it follows the path of the jet stream.

However, sometimes the stream distorts. Named for a shape that resembles the last Greek letter, an omega block transpires when two large regions of low pressure sandwich a large region of high pressure. As a general rule, high pressure brings pleasant weather, filled with dry air and nice temperatures; conversely, low pressure totes rainier weather. In meteorology, blocks are large-scale patterns in the atmospheric pressure field that tend to remain stationary. If the jet stream functions as normal, highs and lows move across the continent with some regularity. When a block sets up, these areas might stay put for days or weeks. If you happen to be in a place where good weather occurs, you rejoice. If you sit in less-than-ideal conditions, you wonder when it will end.

An omega block happened to pitch a tent over North America this year. Where we live, the high pressure kept things nice and dry. Humidity was an afterthought.

With the recent positioning of the omega block, instead of blowing west-to-east, the jet stream plunged north-to-south. With the surrounding regions “blocked” by the stationary pressure systems, the smoke could only follow the jet stream, which meant pouring down into the Great Lakes and eastern seaboard.

Here in Ohio, we finally received some rain over the weekend, perhaps signaling the end of the omega block.

As with many things in life, the omega block giveth and the omega block taketh away. It brought in a period of low humidity, but also produced a scene of apocalyptic smokiness. We won’t miss the smoke, but we’ll have to make do as corn sweat becomes the modality du jour.

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