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500hPa Heights Falls + Thunder Reports

05 May 2023 05:30 AM
With hopefully a return to thunderstorms in store over the coming days, the featured chart takes a bit of a deep dive into some meteorology regarding thunderstorm forecasting. A vital set of observations to understand the state of the atmosphere are the twice daily soundings taken by the NWS. These soundings report observations at mandatory pressure levels as the balloons ascend to help produce consistent spatial analyses over the globe. Perhaps the most important pressure level for meteorologists is 500 hPa, which is approximately a half way point (from a mass perspective) and often can provide insights into atmospheric stability and steering currents to forecast storms. The vertical height above sea level and how it is changing with time can yield first pass assumptions on if the air in the column is rising or sinking. For storms, rising air is desired. So the featured chart compares the 12 hour change in 500 hPa height and if thunder was observed over this same 12 hour period based on sounding and METAR/airport data from Omaha, NE. The data is partitioned by month and if thunder was or wasn't observed. The data is presented as split violin plots, so to give a sense of the distribution of the values. An important note is that the two sides are not equally scaled. The labels near the bottom indicate the percentage of thunder cases that coincided with decreasing heights. Whew! So what insight does this chart provide? First, it is clear that decreasing heights are dominant for thunder cases during the cold season. They are less coincident during the summer season, how could that be? The scale of the storm systems involved is the explanation as cold season thunder activity is associated with large storm systems that will be easily sampled by the twice daily soundings. During the summer time, thunderstorm complexes are smaller scale and driven by more subtle features in the atmosphere, which are not easily diagnosed by twice daily soundings.

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Tags:   meteorology   sounding   thunder