Surface layer characteristics of thunderstorm outflow

Abstract

The objective of this study is to define the turbulent characteristics of thunderstorm outflow winds in the surface layer. Thunderstorms are one of the most common types of severe weather, and the climatological record for many stations shows many extreme wind events can be identified as having been generated by thunderstorms. However, until recently it has proved difficult to separate which high wind events are caused by thunderstorm outflows, and which are generated by typical extratropical low-pressure systems. The advent of the Doppler weather radar and the deployment of a national network of these radars across the continental United States provides a powerful new tool for the classification and analysis of thunderstorm outflow events.

Studies have shown that in many locations the strongest winds on record are generated by thunderstorms (Twisdale and Vickery, 1992, 1995). In many cases, these straight-line winds can cause damage similar to that caused by tornadoes. Besides causing structural damage near the surface, the lifting of less dense ambient air by thunderstorm winds can be the focusing and/or riggering mechanism for further thunderstorm development to occur. It is the modification of the environment surrounding the storm, and the localized nature of the outflow and cloud system that has made the investigation and forecasting of thunderstorms difficult. It is possible to be very near a severe thunderstorm and yet not feel the effects of the rain, hail, or outflow winds. In many cases the thunderstorms are not captured by the surface observation network that the National Weather Service (NWS) has set up to observe weather systems that occur on much larger scale.