May 21 - July 30
Exploring Great Plains Nocturnal Low Level Jet Heterogeneity and Connections to Convection Initiation
Michelle Spencer, Elizabeth Smith, and Petra Klein
What is already known:
- The nocturnal low-level jet is a strong wind which forms just a few hundred meters above the ground on many nights over the Great Plains.
- The nocturnal low-level jet can provide the heat, moisture, and winds that are needed for rainfall and severe storms over the middle of the continent.
- Past research has connected nocturnal low-level jets to the initiation of convective storms, but the connections were broad and did not explore complexities in nocturnal low-level jet structure.
- New research has shown heterogenous structure of the nocturnal low-level jet and suggested connections to storm development, but it is still unknown how common these structures are.
What this study adds:
- This study shows that nocturnal low-level jet heterogeneity is a more common feature than previously documented in the literature.
- The heterogenous nocturnal low-level jet can be a driver for nighttime convection that occurs away from other triggering mechanisms.
- The nocturnal low-level jet and its heterogeneity should be taken into consideration when forecasting nighttime convection.
Abstract:
Observations from six nights of the 2015 Plains Elevated Convection At Night (PECAN) field campaign were used in this study to investigate the heterogeneity of the nocturnal low-level jet and draw possible con- nections between a heterogeneous jet and nocturnal convection initiation. The Great Plains region of the United States often experiences a nighttime precipitation maximum during the summer months, with some of the maximum being contributed to by convection that initiates overnight. Current understanding of the processes leading to nocturnal convection initiation is limited, but it is believed the nocturnal low-level jet may be playing an important role. The six cases chosen for this study showed clear diagonal striation sig- natures, suggesting the nocturnal low-level jet is heterogeneous in structure and the heterogeneity is much more common than previously thought. This signified a change in the structure of the nocturnal low-level jet and a missing component to past low-level jet climatologies. Additionally, a case study of one of the six cases showed evidence that the nocturnal low-level jet may be acting as a forcing mechanism for nocturnal convection initiation observed in the absence of other forcing mechanisms. The nocturnal low-level jet and its heterogeneous spatial-temporal evolution should be taken into consideration when forecasting for nocturnal convection initiation, especially in the absence of more traditional trigger mechanisms.