This thesis was funded by a scholarship from the Faculty of Engineering and Physical Sciences, University of Manchester and is presented in an alternative thesis format. The thesis consists of three separate journal articles which form a coherent research project. Paper 1 is a climatology of tornadoes in the British Isles from 1980-2012. The climatology included interannual variability, seasonality, diurnal cycle, intensity, location of occurrence, sounding-derived environmental parameters, and parent storm types of tornadoes. One finding from Paper 1 was that the most common parent storm type in the British Isles was linear storms, for example, storms forming along cold fronts. This finding motivated Papers 2 and 3, which studied vortexgenesis in a tornadic narrow cold-frontal rainband (NCFR), a storm type common to the British Isles, which occurred 29 November 2011. This NCFR caused seven tornadoes across Wales and England. Paper 2 compares the differ- ences in WRF simulation runs of the NCFR based on initialization time, planetary boundary layer scheme, microphysics scheme, and land surface scheme. Out of 96 simulations, the most realistic (most similar to observed radar reflectivity) run was chosen for a case study in Paper 3. Paper 3 analyzes vortices along the NCFR to determine mechanisms dominating their formation and maturation.

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This thesis explores the relationship between surface elevation roughness and tornado frequency throughout the eastern United States. It builds upon previous studies which demonstrated a negative relationship between roughness and tornado frequency for the Great Plains and Arkansas. A generalized linear model with tornado frequency as the response variable and roughness and population density as the predictors is generated. This model demonstrates that increased roughness is associated with decreased tornado frequency at the scale of the entire eastern United States, especially where roughness is greater than 20 meters. The methods are also performed for 13 smaller regions within the eastern US, but an effect of roughness is only confirmed for the regions encompassing the Great Lakes and central Appalachians. From these results, it is concluded that mountain ranges, where roughness exceeds 20 meters, clearly inhibit tornado activity, but there is little evidence that smaller terrain variations have the same effect.

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Tropical cyclone (TC)-spawned tornadoes in Florida were analyzed to determine patterns of occurrence based on storm and geographic features. Tornadoes were determined to be associated with a landfalling or nearby TC if a tornado occurred within 800 km of the TC’s center of circulation. TC-tornadoes were analyzed for patterns based on distance and angle from TC’s center, topographic influences, population biases, and influence based on time of landfall. Most TC-Tornadoes tend to occur more often before landfall than after. It was discovered that tornadoes have occurred in different areas with respect to the bearing from the center depending on the landfall location and time of landfall. It was also discovered that land use type, and elevation had little to do with TC-Tornado occurrence. The results do suggest some population bias. The findings will be a guide for operational meteorologists to aid in forecasting likely tornadogenesis from TCs.