Spatial Patterns of Turbulence near Thunderstorms

Many people have a turbulence story: perhaps a specific memorable experience or just an unpleasant flight where the seatbelt sign remained on for hours. While more rare, severe turbulence encounters can result in serious (even fatal) injuries and significant operational costs to airlines. While storms themselves are highly turbulent, they can also modify their environment in ways that lead to turbulence far from the storm. Using limited datasets, past studies indicate moderate or greater (MoG) turbulence can extend beyond current federal guidelines for avoidance (20 mi or 32 km), but many questions remain. For example, 1) What is the spatial distribution of turbulence relative to storms? 2) What environmental factors influence the spatial distribution? Now, extensive archives of radar data and automated turbulence reports from commercial aircraft allow us to thoroughly investigate turbulence near storms. To this end, we compare turbulence reports to storm locations over 9 years (2009-17) in the United States. We find that 32 km from 10-dBZ echoes at flight altitude, the risk of MoG turbulence is nearly 5 times the background occurrence and that elevated risk extends beyond 100 km. At 2 km above echo tops, the risk of MoG turbulence exceeds 20 times the background risk. This decreases exponentially but remains elevated at all vertical separation distances. Risks increase with storm intensity. Finally, when we use ERA5 reanalysis to assess environmental factors, we find increased risk with stronger mean wind and wind shear, with slightly higher risk downstream and to the left of the wind/shear vector.