Heat burst along the Kansas River
A very rare event occurred in southern Geary and Riley counties overnight Wednesday and into Thursday, June 15-16, 2016. With all significant thunderstorms to the far south and east, a strong wind event occurred. Winds gusted up to 70 mph at the Manhattan Airport, 56 mph at Fort Riley Airport, and 52 mph at the Ashland Bottoms mesonet station. Damage to power lines and trees were reported by the Geary County Emergency Manager.
So what caused this unique event? Coinciding with the strong winds, a non-diurnal temperature change occurred, along with a drop in moisture. From 7:30 p.m. to 11 p.m., temperatures rose anywhere from 10-15 degrees F and relative humidities dropped more than 60-70% (see the below graph from the Ashland Bottoms Kansas Mesonet station). Typically as the evening progresses, temperatures should drop and relative humidity should climb. What caused this unusual change was a heat burst.
Figure 1. Temperature, relative humidity, and wind gusts at Ashland Bottoms Wednesday night into Thursday morning, June 15-16, 2016. Data source: www.mesonet.k-state.edu
Heat bursts: A heat burst is a rare phenomenon that occurs with dissipating thunderstorms. A thunderstorm downburst occurs when, due to latent heat of evaporation, precipitation cools as it falls and the denser air mass plummets to the ground. When a thunderstorm dissipates, all the moisture can be completely evaporated on the way to the ground. The air can no longer cool, due to the lack of precipitation, and adiabatic compression occurs as it falls. This compression heats the air (sometimes significantly) and coincidently decreases the moisture content. The hot air will often slow its progression to the surface due to lack of temperature difference between atmosphere and the downdraft. However, if sufficient momentum is built prior to the heating, it can reach the surface with very strong winds. Exactly what happened on the night of June 15-16!
Christopher Redmond, Kansas Mesonet Network Manager
Mary Knapp, Weather Data Library
National Weather Service, Norman, Oklahoma: “All About Heat Bursts,” http://www.crh.noaa.gov/oun/?n=heatburst_info, 2011.