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Tornado outbreaks (TO) occur every year across the continental United States and are a result of various synoptic scale, mesoscale, and climatological patterns. This study looks to find what patterns exist among the various scales and how that relates to the climatology of the TOs. In order to find these patterns, principal component analysis (PCA) and a cluster analysis were conducted to differentiate the patterns of data. Four distinct clusters of TOs were found with varying synoptic and mesoscale patterns as well as distinct climatological patterns. An interesting result from this study includes the shifting of TO characteristics over time to a more synoptically forced pattern that has becoming stronger and shifted eastward from the Great Plains.

UNSTABLE was a field project in the summer of 2008 to better understand the large-scale and mesoscale forcings of summer storms. This thesis objective is to better understand boundary layer characteristics and convective environments in the Alberta foothills. Three sub-objectives are designed to address the overall thesis goal: (1) Characterize the daily evolution of the boundary layer during different convective regimes, (2) distinguish conditions between days with deep, shallow and no convection, and (3) to illustrate how targeted soundings can be useful for severe storm prediction. Non-convective days exhibited a warmer atmospheric column. Days with shallow convection exhibited a mid-level inversion. Deep convective days commonly displayed unstable low-levels and cooler upper levels, deep low-level moisture and the mountain-plains circulation. When compared to the pre-existing operational upper air network, mobile UNSTABLE soundings better captured the near storm environment of two tornadic events in terms of available instability and shear profiles.

During the April 25 – 28, 2011 severe weather outbreak, 350 tornadoes were confirmed across 21 states, making the event the largest 3-day outbreak in U.S. History. Of the 350 tornadoes, 13 were of EF4 or EF5 strength. Due to complex terrain and vegetation in northeastern Alabama, northwestern Georgia, and eastern Tennessee, only four tornadoes were analyzed in this study. Abrupt changes in vegetation and the related sensible and latent heat fluxes have been shown to enhance convective activity along and near the resulting land surface discontinuities. This study analyzed heightened convective activity (analyzed by looking at cloud-to-ground lightning data) along each tornado track on days of weak synoptic forcing. Post- tornado months showed no signs of enhanced convective activity along any of the tornado tracks analyzed in this study, which could be attributed to several factors including study period, duration of intensity, tornado track length and width, and land cover.

The Madden-Julian Oscillation (MJO) is the leading mode of tropical intraseasonal variability and has known links to modification of extratropical patterns. Spatial and temporal scale differences between the MJO and US tornadoes makes connecting the two difficult, but using tornado outbreaks (TO) that are typically synoptically evident helps close this gap. An assessment of TO probability was conducted for each of the eight Realtime Multivariate MJO index phases for each month. In addition, clusters of TOs were used to identify how the MJO’s extratropical response influences patterns that lead to outbreaks in the US. It was found, and in part, consistent with previous research, that the shifts in the jet stream and wave breaking over the Pacific that occur in response to the current location of the MJO convection and circulation anomalies contribute to changes in the mid-latitude flow that can produce TOs in the central and eastern US.

During 2007 – 2015, a total of 2,359 tornado watches were issued by the Storm Prediction Center and 10,840 tornadoes were confirmed. The objective of the first part of this study analyzed the accuracy of tornado watches for the nine-year period of 2007 – 2015. In addition to accuracy, fatalities, lead times, valid watch times, and areas were calculated for each tornado watch. 58.80% of the tornado watches had at least one tornado inside the tornado watch and 27.43% had at least one tornado outside the tornado watch. Of the 10,840 tornadoes, 56.70% were inside a tornado watch, 9.69% were outside a tornado watch, and 33.62% occurred when there was no tornado watch in effect. The average valid time for a tornado watch was 6 hours and 50 minutes and the average lead time for a tornado was 2 hours and 8 minutes. The second objective utilized a survey to determine participant knowledge and better understand “watch severity response”. A majority of the survey respondents accurately identified the difference between a tornado watch and a tornado warning. Most of the respondents described their weather knowledge as ‘moderately knowledgeable,’ ‘very knowledgeable,’ or ‘slightly knowledgeable.’ TV meteorologists, the NWS, and weather apps are the most common sources for daily weather information and information regarding a tornado watch. 81.63% of the respondents correctly identified if they were under a tornado watch during 2016. As the severity of the watch or the length of the activity increased, the likelihood of the respondent continuing the activity decreased. 38.87%, 54.76%, and 79.18% of the respondents ‘probably would not’ or ‘definitely would not’ continue an activity, lasting any duration, during a severe thunderstorm watch, a tornado watch, or a PDS tornado watch, respectively. The final objective attempts to categorize simple economic response to various watch severity types. The percent of respondents who would not continue an activity, based on the severity of the watch, was applied to a variety of watches that occurred during 2016. The economic loss associated with a watch ranged from $498,332.15 – $107,126,919.19.

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.

The goal of this study is to improve seasonal tornado outbreak forecasting by creating a statistical model that forecasts tornado outbreak frequency in the US using teleconnection indices as predictors. For this study, a tornado outbreak is defined as more than 6 tornado reports associated with a single synoptic system and an event N15 rating index of 0.5 or higher. The tornado outbreak season is confined to all months after February for a given calendar year. Monthly teleconnection indices are derived from a rotated principal component analysis (RPCA) of the geopotential height fields. Various regression techniques were trained with a sample of monthly teleconnection indices, tested on new data, and optimized to achieve the highest predictive skill. The outcome of this study could potentially allow forecasters the ability to predict tornado outbreak potential on a climatological scale with months of lead-time, allowing for better preparation strategies for tornado outbreak seasons.

A better understanding of the performance in precision of physical parameterizations in NWP models is necessary for improving forecasts of tornadic outbreaks. For this study, WRF simulations of tornadic outbreaks were run using configurations of three microphysics, three convective physics, and two PBL physics schemes. Each configuration was subjected to ten iterations of SKEBS. The means of the ten perturbation members of each parameterization configuration were bootstrapped for SB CAPE, SB CIN, and 0-3km SRH to find 95% confidence interval widths at each grid point. Maps of these spreads provided a spatial analysis of the uncertainty. Analyses on correlations and clusters were performed to determine how the configurations related spatially and in magnitude. These uncertainties were further bootstrapped to compare the mean of each configuration in boxplots. The effect on the uncertainty produced by each configuration varied according to the diagnostic variable being analyzed.

Oklahoma is in the middle of Tornado Alley, a name resulting from the large number of tornadoes that hit the region yearly. These storms are costly to life and property. The housing in Oklahoma is currently not well enough engineered to withstand tornados. This thesis proposes a three stage response combining construction technology and the use of landscape to better protect the homes and residents of Oklahoma.