Sensitivities of the Weather Research and Forecasting (WRF) model in forecasting low-level jet events and the impact on forecasting severe weather

Nocturnal low-level jets (LLJs) are common features observed in the Great Plains region of the United States. LLJs play a key factor in initiating and sustaining mesoscale convective systems and other severe convective storm modes in the Great Plains. It has been previously shown that the LLJ is important source of water vapor over the Great Plains. The moisture convergence associated with LLJs has been shown to be linked to summer rainfall over the central United States. The widespread flooding in the central United States during the summer of 1993 has been linked to the strong southerly LLJ during this time.

To forecast LLJs, accurate representation of the PBL is crucial, which is also important for being able to forecast many high impact events. Accurate representation of the LLJ can help forecasters predict where severe weather will initiate. At present, NWP models face a challenge in precise forecasting of the development, magnitude, and location of LLJs. This is due to the fact that LLJs are common during nighttime stable boundary layers, and there is a general consensus among researchers that our contemporary understanding and modeling capability of this boundary layer regime is quite poor. In the present work, we investigate the potential of a new generation NWP model called the Weather Research and Forecasting (WRF) model in simulating an LLJ event and associated stably stratified boundary layer observed over the Southern High Plains of western Texas on June 2nd, 2004. During this night, over a period of 8 hours (from 04 to 12 UTC), two distinct low-level jet structures with wind maxima of greater than 16 ms-1 were observed. An extensive array of in-house monitoring systems (consisting of the West Texas Mesonet, a 200 m tall instrumented tower, and a boundary layer profiler) is effectively utilized to study this event in great detail and assess the performance of the WRF model with different model configurations. The WRF model is computationally efficient and its state-of-the-art two-way nesting capabilities allowed us to employ extremely fine grid resolutions at the regions of interest. Our results indicate that the WRF model can capture some of the essential characteristics of observed LLJs. Surface characteristics, such as 2 m temperature, upward heat flux, and 10 m wind speed, were also investigated to determine if any discrepancies in the two boundary layer schemes investigated, MYJ and YSU, were present.