Wind Farms Can Modify Thunderstorm Outflow Boundaries

On June 18, 2019 around 0100 UTC, National Weather Service (NWS) radar reflectivity indicated the presence of thunderstorm-generated outflow propagating east-southeast north of Lubbock, Texas. A section of the outflow boundary that encountered a wind farm experienced a notable reduction in propagating speed, suggesting that the wind farm impacted the outflow boundary progression (Figure 1). This impact could be due to the increased roughness of the wind turbines, the wake wind speed deficit from individual turbines, or the increased turbulence due to the wind farm wakes, or other processes.

Using this incident as a test case, we use the Weather Research and Forecasting model and its Wind Farm Parameterization to explore this behavior and address the extent to which wind farms can modify meteorological features like thunderstorm outflow boundaries. We first conduct a set of four simulations to explore the sensitivity of the outflow boundary to the wind farm roughness: one with no wind turbines; one with 2-MW turbines as deployed in reality; one with more 2-MW turbines than actually deployed; and one with larger, 10-MW turbines. We specifically investigate impacts on near-surface wind speed, wind direction, and temperature, in addition to changes to precipitation features as the storm and associated outflow pass over the wind farm domain.

Additionally, we assess how agreement with observations depends on model settings such as turbine-induced turbulent kinetic energy and vertical resolution. The NWS radar and nearby West Texas Mesonet surface stations provide observations for validation of the simulations.