What is “low wake”?

Eastern Nebraska and southwestern Iowa were hit by multiple rounds of severe weather from Tuesday night into Thursday morning. These produced large hail, strong winds, and even a few tornadoes. However, the rain held off in the Omaha metro heading into western Iowa, but high winds did blow. At Offutt AFB in Bellevue, a 62 mph wind gust was recorded when the rain ended. Other reports of 30-40 mph winds were seen across the metro into western Iowa. What happened? Why did it become windy after the rain ended? The answer comes from a somewhat uncommon climate phenomenon known as a “dip.” But what is low wake? How are they formed? What happens in a low wake state?

You are probably familiar with high and low pressure systems, which are the primary drivers of the country’s weather. If we are under a high pressure area, expect calm conditions with sunshine and light winds. If we are under low pressure, the weather gets a little rougher.

The relationship between wind and pressure is crucial to awakening the lows. The atmosphere is constantly trying to balance itself in terms of pressure, so winds in areas of high pressure and low pressure try to move to find balance. In high pressure situations, the air moves down and out to try to lower the pressure. The opposite is the case for low pressure, as air rushes in to fill the low-pressure vacuum inside. These changes in pressure are what not only give us wind, but also keep the weather constantly changing.

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Now take those same mechanics, but reduce them to storms. Thunderstorms contain areas of low and high pressure, where air pushes inward and upward to form updrafts, and downward to form downdrafts (where rain falls). In the downdraft, high pressure areas are formed. Many thunderstorm complexes, like the one that developed in Omaha Thursday morning, carry their own areas of high pressure.

Sometimes, low pressure can develop behind areas of thunderstorms. This is your level of wakefulness, as it develops in the aftermath of a thunderstorm. As mentioned earlier, the air will try to rush away from the high pressure towards the low pressure areas to try to balance each other out. If the difference in pressure is large enough, it can cause large gusts of wind. Most of the time, it stays above the surface, but sometimes it collapses. That was the case Thursday morning in eastern Nebraska and western Iowa.

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How do we know this? Well, there are two things that can tell us that a low level of awakening is occurring. The first, of course, is actual wind gusts. Behind the front, winds were common at 30-45 mph in the minutes after the rain ended. Omaha Eppley recorded 40 mph wind gusts. The strongest wind gust in Bellevue occurred at Offutt AFB, where a 62 mph wind gust was recorded in the minutes following the storm.

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The biggest indicator of what happened is the change in pressure. Below are pressure readings taken from Offutt AFB, Eppley, Nebraska City, Plattsmouth, Council Bluffs, Red Oak, and Atlantic. Notice how the pressure rises briefly before falling sharply? This is low wake access! It’s fast, and within an hour my pressure levels were back to normal.

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KMTV

KMTV

Low wake levels are sometimes difficult to predict because they can form seemingly randomly, but with better equipment such as weather stations that record this data, they are becoming easier to find.