Relationship between the forecast skills of the Great Plains low-level jet and mesoscale convective systems in 4 km WRF runs

Brian Squitieri
Iowa State University 
Noon January 20 in Room 2155

The Great Plains low-level jet (LLJ) fosters an environment that is supportive of nocturnal mesoscale convective systems (MCSs) across the central U.S. during the summer months. The goal of this research was to determine if forecast skill in the LLJ correlates to forecast skill in MCS precipitation in high spatial resolution (4 km) WRF runs. LLJs were classified based on total wind magnitude and synoptic background. Both cyclonic flow and inertial oscillation driven LLJs were included in this study. It was found that the forecast skill of the geostrophic and ageostrophic wind direction components correlated positively with statistical significance to forecast skill of MCS precipitation. The diurnal geostrophic wind maximum across the plains (induced by terrain sloping and heating) set up the background flow for the LLJ to develop and established the orientation of the LLJ (which would impact MCS evolution). The forecast skill in the ageostrophic wind direction correlated to MCS precipitation forecast skill since the ageostrophic winds induced convergence at the terminus of the LLJ, which benefited MCS longevity only if the ageostrophic wind held a perpendicular component to the MCS. No significant correlation was found between MCS precipitation forecast skill and the forecast skills of 700 hPa temperature advection, mixed layer convective available potential energy, mixed layer convective inhibition, 0-1 km, 0-3 km and 0-6 km shear along with surface and 850 hPa frontogenesis and horizontal moisture flux convergence.