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Abstract Supercell storms are recognized to account for a disproportionately large amount of severe weather occurring in the United States and elsewhere. Despite their importance, few studies document their climatological behavior, and those that do focus predominantly or entirely on severe supercells. This study presents an objective and comprehensive radar-based climatology of supercell storms during a 14-yr period over the contiguous United States. Approximately 56 000 supercells are identified, half of which are likely nonsevere. All objectively identified supercells (strongly and persistently rotating storms) are diagnosed as either “right moving” (RM) or “left moving” (LM) based primarily on the deviance of storm motion relative to the 0–6-km environmental wind shear vector. RM supercells outnumber LM supercells at a rate of approximately 3:1 and also live longer. RM supercells are more frequently severe than LM supercells, accounting for ≈99.8% of supercell tornadoes, ≈76.9% of supercell severe hail events, and ≈68.9% of supercell severe wind events. Common to both supercell configurations, numerous sensitivities are identified between storm characteristics and storm severity. Namely, storm severity increases with increasing velocities of storm motion and increasing midlevel rotation. Severity maximizes when storm motion deviates ≈30° left or right of the 0–6-km environmental wind shear vector. Last, severe and nonsevere supercell storm characteristics are compared, and the greatest discriminatory indicators are based on metrics of the depth of high radar reflectivity magnitudes. Significance StatementRotating thunderstorms (supercells) are responsible for the vast majority of the most significant tornadoes and severe hail events in the United States. Despite their recognized importance, many basic details about them remain unknown, such as their frequency, spatial distribution, and dominant character of motion (right or left moving). In this study, a comprehensive 14-yr statistical analysis of United States supercell storms based on objectively analyzed radar observations is used to address this gap in understanding. Numerous sensitivities between supercell severity and storm characteristics are found and have potential to advance the warning decision-making process.
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Notable impact of wildfires in the western United States on weather hazards in the central United States
Increased wildfire events constitute a significant threat to life and property in the United States. Wildfire impact on severe storms and weather hazards is another pathway that threatens society, and our understanding of which is very limited. Here, we use unique modeling developments to explore the effects of wildfires in the western US (mainly California and Oregon) on precipitation and hail in the central US. We find that the western US wildfires notably increase the occurrences of heavy precipitation rates by 38% and significant severe hail (≥2 in.) by 34% in the central United States. Both heat and aerosols from wildfires play an important role. By enhancing surface high pressure and increasing westerly and southwesterly winds, wildfires in the western United States produce ( 1 ) stronger moisture and aerosol transport to the central United States and ( 2 ) larger wind shear and storm-relative helicity in the central United States. Both the meteorological environment more conducive to severe convective storms and increased aerosols contribute to the enhancements of heavy precipitation rates and large hail. Moreover, the local wildfires in the central US also enhance the severity of storms, but their impact is notably smaller than the impact of remote wildfires in California and Oregon because of the lessened severity of the local wildfires. As wildfires are projected to be more frequent and severe in a warmer climate, the influence of wildfires on severe weather in downwind regions may become increasingly important.
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- Award ID(s):
- 2103714
- PAR ID:
- 10414739
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 119
- Issue:
- 44
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1073/pnas.2207329119
