Portland State University. Department of Geography
Date of Award
Master of Science (M.S.) in Geography
1 online resource (x, 42 pages)
A 30-year climatology of lightning and associated synoptic meteorological patterns are characterized across the Western United States (WUS), utilizing a comprehensive composite analysis. Results generally show a preferred synoptic meteorological setup with positive 500-hPa geopotential height anomalies to the northeast of the location experiencing a lightning day, and negative sea level pressure anomalies co-located and to the northwest. Variation in preferred anomaly patterns across the western US reflects the divide between those areas affected by the North American monsoon system and areas outside the monsoonal core. Locations in the western Great Basin and northern Rocky Mountains, which are outside the monsoonal core, show preference toward greater amplitude of synoptic circulation fields compared to the interior Southwest. A northwest-to-southeast gradient in magnitude of anomalies of moisture and mid-tropospheric instability is present, with areas northwestward showing preference for greater departures compared to climatological means. These results likely reflect the prevalence of favorable mesoscale dynamics key to lightning during warm season months in locations within the monsoonal core in the interior Southwest, along with the more episodic nature of lightning-conducive features in areas peripheral to this region. Meteorological patterns for select locations are explored in more detail and two case studies of notably active lightning events are presented. This work provides an observation-based foundation for understanding meteorological patterns on lightning days, which may inform operational forecasts for lightning hazards as well as projected changes in lightning activity across the western US from climate model simulations.
Kalashnikov, Dmitri Alexander, "A 30-Year Climatology of Meteorological Conditions Associated with Lightning Days in the Western United States" (2019). Dissertations and Theses. Paper 5430.