If you were outside between 4 and 5 a.m. earlier, you might have felt something strange. All of a sudden it got hot and a little breezy. If you think you are feeling things, you are not alone. Suddenly, Eppley Airfield jumped from 81 to 88 degrees within 15 minutes. What happened? The answer might lie in a heat burst or heat burst-adjacent event. Let's dive into it.
First, what happened? At 4 a.m., Eppley Airfield sat at 81 degrees with a dew point of 72. It was already warm and gross, but then things changed. At 4:15, the temperature was still at 81. By 4:20, it was 84; then by 4:25, it had jumped to 88 degrees where it held for the rest of the hour. A 7-degree jump in temperatures within 10 minutes? That is very unusual, particularly at 4 a.m. Likewise, our dew point temperature dropped from the low 70s to the mid-60s at the same time, likely allowing for the air to warm up.
Two important things to note: 1.) It got a bit breezy after the warm up with occasional wind gusts to 25mph. And 2.) It was very localized to Eppley, as other observation sites across the metro did not suddenly warm up. So, what accounted for this?
Some can attribute this phenomenon to a heat burst. A heat burst is often caused by dying thunderstorms. When the rain evaporates in a layer of dry air, it causes the air to cool. Since cooler air is denser, it rushes towards the ground compressing the warmer air closer to the ground, increasing its temperatures. We commonly see this in the desert southwest of the US, as well as over western and central Nebraska. These can sometimes be extreme, raising the temperature of a specific location by as much as 20-30 degrees in a few minutes. Last year, a heat burst affected York.
There is one big question that remains from this morning. There was no dying thunderstorm over Omaha to cause a traditional heat burst. So, what other explanation? The answer might lie in the low-level jet, a belt of faster-moving air within the lower levels of the atmosphere which normally increases at night. You can find out more about the low-level jet here. This morning, the low-level jet was moving at roughly 45 knots (51mph) less than 1km off the surface.
Likewise, right above the surface, there was a pronounced inversion in our temperatures. Inversions commonly happen at night, since the surface cools faster than the air above, we often get a layer of cool air that sits atop a layer of warm air. On nights when it is clear and no wind, moisture-laden surfaces under inversions can oftentimes produce fog.
So, all that long-winded explanation to get to this. Right above the surface, the air was much warmer and drier than at the surface, with winds around 51mph. By some mechanism that inversion and winds were briefly transferred to the ground around Omaha. This is what caused our quick warm-up within 10 minutes!
