Capturing strong downbursts from a supercell in Kansas City
Understory’s RTi weather station network has captured evidence of a downburst in Kansas City! A downburst is a powerful weather phenomenon that can result in straight-line winds reaching 150 mph with the damage potential of a tornado. Although the dangers of tornados are notorious, there are approximately 10 downburst damage reports for every one tornado report in the U.S., encouraging us to take note of any downbursts we observe.
The downburst we observed occurred during a thunderstorm on July 15, 2015, which entered the southwest side of the city first, moving east, and then began to dissipate while moving toward the northeast. The thunderstorm triggered the downburst when dry air entered the thunderstorm. Rain evaporated, cooling the dry air, which increased the density, causing the air mass to plunge toward the ground. When the cool, dry air hit the surface, a gust front expanded in all directions, with the strongest winds travelling in the direction of storm movement (northeast in this case).
We know when the gust front arrived at each RTi weather station by the rise in wind speed, and drop in both temperature and humidity caused by the fast-moving, cold, dry air. Examining our wind data reveals the sharp arrival of a gust front that progressed from southwest to northeast across Kansas City. The station that measured the strongest gust front recorded a 3-second sustained gust of 57mph, a temperature drop of 78°F to 71°F (unusual for 9 AM), and a humidity drop of 91.75% to 80.85%. We measure relative humidity, which is the percentage of water vapor in the air currently, compared to the amount needed for saturation at the current temperature. This implies a negative relationship, because colder air can hold less water than warmer air. Usually, when temperature decreases, relative humidity will increase, but in the case of the downburst, both temperature and humidity fall as the stations register the cold, dry gust front.
The first stations to be hit by the gust front (in the SW of Kansas City) were the closest to the origin of the downburst, so they recorded higher wind speeds, and larger temperature and humidity drops. As the gust front expanded towards the northeast and dissipated, the stations documented a weaker rise in wind speed and drop in temperature, although the dry air still caused a clear decrease in pressure.
Our station density within Kansas City allows us to track the movement of the storm across the city. The time delay of the gust front between our stations as well as wind direction gives us information about how the storm progressed and dissipated. Only 21 of the 25 stations in Kansas City felt the gust front, revealing the gust front did not expand to the north of the city. By mapping the times the gust front arrived at each station, we can visualize the path of the storm.
We are producing an impressive quantity of data that can be used to track storms across cities and assess property damage. Our RTi weather station network allows us to see exactly where damage occurred and what properties a storm affected. Our property-level damage analytics portal gives a summary of storm damage and gives you the tools to understand how to react in a fast and efficient manner. Below is a page from our platform detailing the events of the downburst in Lenexa, Kansas.