Abstract
Although environmental controls on bulk supercell potential and hazards have been studied extensively, relationships between environmental conditions and temporal changes to storm morphology remain less explored. These relationships are examined in this study using a compilation of sounding data collected during field campaigns from 1994 to 2019 in the vicinity of 216 supercells. Environmental parameters are calculated from the soundings and related to storm-track characteristics like initial cell motion and the time of the right turn (i.e., the time elapsed between the cell initiation and the first time when the supercell obtains a quasi-steady motion that is directed clockwise from its initial motion.). We do not find any significant associations between environmental parameters and the time of the right turn. Somewhat surprisingly, no relationship is found between storm-relative environmental helicity and the time elapsed between cell initiation and the onset of deviant motion. Initial cell motion is best approximated by the direction of the 0–6-km mean wind at two-thirds the speed. This is a result of advection and propagation in the 0–4- and 0–2-km layers, respectively. Unsurprisingly, Bunkers-right storm motion is a good estimate of post-turn motion, but storms that exhibit a post-turn motion left of Bunkers-right are less likely to be tornadic. These findings are relevant for real-time forecasting efforts in predicting the path and tornado potential of supercells up to hours in advance.
Significance Statement
Most of the strongest and deadliest tornadoes are produced by a type of thunderstorm called a “supercell.” Forecasters use many tools to help diagnose which environments favor supercells and which do not. However, given conditions favorable for supercells, we do not know much about how the supercell will evolve in time. This study identifies relationships (or the lack thereof) between background conditions and developing supercells, particularly related to storm path. Surprisingly, despite well-established relationships between supercell characteristics and the environment, we do not find any significant relationships between environmental parameters and changes in the supercells’ paths early in their life cycles. These findings are relevant for forecasters tasked with predicting supercell paths up to hours in advance.
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