Department Personnel

Walker Ashley

   Walker Ashley     

       washley@niu.edu 

 

Publications, Grants and Presentations


Publications

Gensini, V. A., and W. S. Ashley, 2011: Climatology of potentially severe convective environments from reanalysis. Electronic Journal of Severe Storms Meteorology, 6(8), 1-40. Abstract

Ashley, W. S., M. L. Bentley, and J. A. Stallins, 2011: Urban-induced thunderstorm modification in the Southeast United States. Climatic Change, DOI: 10.1007/s10584-011-0324-1. Abstract

Bentley, M. L., J. A. Stallins, and W. S. Ashley, 2011: Synoptic environments favourable for urban-enhanced convection in Atlanta, Georgia. International Journal of Climatology, DOI: 10.1002/joc.2344. Abstract

Black, A. W., and W. S. Ashley, 2011: The relationship between tornadic and nontornadic convective wind fatalities and warnings. Weather, Climate, and Society, 3, 31-47. Abstract

Schoen, J., and W. S. Ashley, 2011: A climatology of fatal convective wind events by storm type. Weather and Forecasting, 26, 109-121. Abstract

Spencer, J. M., and W. S. Ashley, 2011: Avalanche fatalities in the western United States: A comparison of three databases. Natural Hazards, doi: 10.1007/s11069-010-9641-3. Abstract 
http://www.springerlink.com/content/h824177u2h522028/
 
Paulikas, M. J., and W. S. Ashley, 2011: Thunderstorm hazard vulnerability for the Atlanta, Georgia metropolitan region. Natural Hazards, doi: 10.1007/s11069-010-9712-5. Abstract 
http://www.springerlink.com/content/n832354853728434/

Schoen, J., and W. S. Ashley, 2011: A climatology of fatal convective wind events by storm type. Weather and Forecasting, 26, 109-121. Abstract 
http://journals.ametsoc.org/doi/abs/10.1175/2010WAF2222428.1

Bentley, M. L., W. S. Ashley, and J. A. Stallins, 2010: Climatological radar delineation of urban convection for Atlanta, Georgia. International Journal of Climatology, 30, 1589-1594. Abstract 
http://onlinelibrary.wiley.com/doi/10.1002/joc.2020/

Black, A. W., and W. S. Ashley, 2010: Nontornadic convective wind fatalities in the United States. Natural Hazards, 54, 355-366. Abstract 
http://www.springerlink.com/content/p32064n752762524/

Gensini, V. A., and W. S. Ashley, 2010: A Reply to “Rip Current Misunderstandings”. Natural Hazards, 55, 163-165. 

Gensini, V. A., and W. S. Ashley, 2010: An examination of rip current fatalities in the United States.  Natural Hazards, 54, 159-175. Abstract 
http://www.springerlink.com/content/q16t26655t504232/ 

Bentley, M. L., T. Stallins, and W. Ashley, 2010: The Atlanta thunderstorm effect. Weatherwise (popular press), 63, 24-29.

Ashley, W. S., and C. W. Gilson, 2009:   A reassessment of U.S. lightning mortality. Bulletin of the American Meteorological Society, 90, 1501–1518. Abstract - Poster

Hall, S.G., and W.S. Ashley, 2008: The effects of urban sprawl on the vulnerability to a significant tornado impact in northeastern Illinois. Natural Hazards Review, 9, 209-219. Abstract

Ashley, W.S., A.J. Krmenec, and R. Schwantes, 2008:  Vulnerability due to nocturnal tornadoes. Weather and Forecasting, 23, 795-807. Abstract - Poster

Ashley, S.T., and W.S. Ashley, 2008:  Flood fatalities in the United States. Journal of Applied Meteorology and Climatology, 47, 805-818. Abstract

Ashley, S.T., and W.S. Ashley, 2008:  The storm morphology of deadly flooding events in the United States. International Journal of Climatology, 28, 493-503. Abstract

Ashley, W.S., and A. Black, 2008:  Fatalities associated with nonconvective high-wind events in the United States. Journal of Applied Meteorology and Climatology, 47, 717-725. Abstract

Ashley, W.S., 2007:  Spatial and temporal analysis of tornado fatalities in the United States: 1880-2005. Weather and Forecasting, 22, 1214-1228. Abstract - Poster

Ashley, W.S, T.L. Mote, and M.L. Bentley, 2007:  An extensive episode of derecho-producing convective systems in the United States during May-June 1998: A multi-scale analysis and review.  Meteorological Applications, 14, 227-244. Abstract

Suckling, P. W., and W. S. Ashley, 2006: Spatial and temporal characteristics of tornado path direction. The Professional Geographer, 58, 20-38. Abstract

Ashley, W.S., T.L. Mote, and M.L. Bentley, 2005: On the episodic nature of derecho-producing convective systems in the United States. International Journal of Climatology, 25, 1915-1932 Abstract

Ashley, W.S., and T.L. Mote, 2005: Derecho Hazards in the United States. Bulletin of the American Meteorological Society, 86, 1577-1592. Abstract

Ashley, W.S., T.L. Mote, P.G. Dixon, S.L. Trotter, J.D. Durkee, E.J. Powell, and A.J. Grundstein, 2003: Distribution of mesoscale convective complex rainfall in the United States. Monthly Weather Review, 131, 12, 3003-3017. Abstract

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Grants, Fellowships and Leaves of Absence:

NIU Sabbatical Proposal: Quantifying hazard exposure: How an increasing and spreading U.S. population is amplifying weather disasters. Submitted July 2011 for leave of absence scheduled for August-December 2012.

NIU Undergraduate Research and Apprenticeship Program, Driving Blind: Vehicular Accidents due to Weather-related Visibility Impairment, Co-PI with Mace Bentley, Fall 2012-Spring 2013

NIU Undergraduate Research and Apprenticeship Program, Climatology of the U.S. Elevated Mixed Layer, Fall 2011-Spring 2012

NIU Undergraduate Research and Apprenticeship Program. Weather Casualties in the U.S., 2000-09. Fall 2010-Spring 2011.

NIU Undergraduate Research and Apprenticeship Program. Storm and Lightning Activity in Georgia, 1997-2006. Fall 2009-Spring 2010, co-PI with M.L. Bentley.

NIU Undergraduate Research and Apprenticeship Program. Contribution of Severe Weather 'Outbreak' Events to the Overall U.S. Hazard Climatology. Fall 2008-Spring 2009.

NIU Research and Artistry Grant. Lightning Fatalities in the United States: An Assessment of Risks and Vulnerabilities. Summer 2008.

NIU Undergraduate Research and Apprenticeship Program. The Development of an Annotated Bibliography of the Climatology of Severe Weather. Fall 2007-Spring 2008, co-PI with M.L. Bentley.

NIU Undergraduate Research and Apprenticeship Program. Spatial Analysis of Weather-related Fatalities in the U.S. Fall 2007-Spring 2008, co-PI with M.L. Bentley.

National Science Foundation, Geography & Regional Science Program and Physical & Dynamic Meteorology Program, Climatological and Event-based Radar Delineation of UHI Convection for Urban Corridors within the Southeastern U.S., co-PI with M.L. Bentley (NIU) and J. A. Stallins (FSU), 2007-2012.

NIU Undergraduate Research and Apprenticeship Program. Spatial and Temporal Analysis of U.S. Tornado Casualties. Fall 2006-Spring 2007.

NIU Research and Artistry Grant. Windstorm-induced Casualties in the United States: 1960-2005. Summer 2006.

NIU Undergraduate Research and Apprenticeship Program. Windstorm-induced Casualties in the United States: 1960-2005. Spring 2006.
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Publications:

Gensini, V. A., and W. S. Ashley, 2011: Climatology of potentially severe convective environments from reanalysis. Electronic Journal of Severe Storms Meteorology, 6(8), 1-40.

This study establishes a U. S. climatology of potentially severe convective environments for the 30-y period 1980–2009 from the North American Regional Reanalysis. Variability of environments supporting significant severe weather is examined for four active severe-weather regions in the U. S. Regional comparisons illustrate potentially significant-severe environments varied greatly both spatially and temporally over the 30-y period of record. The spatial and temporal distributions of significant severe-weather environments and reports are subjectively examined for comparison purposes. While one has to be cautious when linking environments and reports, average calculated significant severe-weather environments show similarities to the annual cycle of significant severe-weather reports. Additionally, mean center analysis indicates that there is no significant shift in the average position of these environments during the period of record.
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Ashley, W. S.  , M. L. Bentley, and J. A. Stallins, 2011: Urban-induced thunderstorm modification in the Southeast United States. Climatic Change, DOI: 10.1007/s10584-011-0324-1.

This study provides the first climatological synthesis of how urbanization augments warm-season convection among a range of cities in the southeastern U.S. By comparing the location of convection in these cities and adjacent control regions
via high-resolution, radar reflectivity and lightning data, we illustrate that demographic and land-use changes feed back to local atmospheric processes that promote thunderstorm formation and persistence. Composite radar data for a 10-year, June–August period are stratified according to specific “medium” and “high” reflectivity thresholds. As surrogates for potentially strong (medium reflectivity) and severe (high reflectivity) thunderstorms, these radar climatologies can be used to determine if cities are inducing more intense events. Results demonstrate positive urban amplification of thunderstorm frequency and intensity for major cities. Mid-sized cities investigated had more subtle urban effects, suggesting that the urban influences on thunderstorm development and strength are muted by land cover and climatological controls. By examining cities of various sizes, as well as rural counterparts, the investigation determined that the degree of urban thunderstorm augmentation corresponds to the geometry of the urban footprint. The research provides a methodological template for continued monitoring of anthropogenically forced and/or modified thunderstorms.
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Bentley, M. L., J. A. Stallins, and W. S. Ashley, 2011: Synoptic environments favourable for urban-enhanced convection in Atlanta, Georgia. International Journal of Climatology, DOI: 10.1002/joc.2344

An examination of synoptic environments conducive to urban thunderstorm development surrounding Atlanta, Georgia, was conducted. Synoptic environmental characteristics were evaluated utilising regional analyses of heights, winds, temperature, and moisture characteristics as well as several thermodynamic variables. A flexible beta cluster analysis was used in order to identify disparate groupings of common synoptic and thermodynamic environments. These groupings were then further analysed through the production of synoptic composites, radar, and lightning distributions. Although the analysis stratified the data by days with weak synoptic flow and maritime tropical airmass characteristics, enough variation existed within the synoptic and thermodynamically grouped parameters to identify four distinct environments present during urban thunderstorms. Environments exhibiting moderate thermodynamic instability were found to produce the highest flash rates and most frequent composite reflectivity days.
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Black, A. W., and W. S. Ashley, 2011: The relationship between tornadic and nontornadic convective wind fatalities and warnings. Weather, Climate, and Society, 3, 31-47.

A database of tornado fatalities, nontornadic convective wind fatalities, severe thunderstorm warnings and tornado warnings was compiled for the period 1986–2007 to assess the spatial and temporal distribution of warned and unwarned fatalities. The time of fatality and location as reported in Storm Data was compared to tornado and severe thunderstorm warnings to determine if a warning was in effect when the fatality occurred. Overall, 23.7% of tornado fatalities were unwarned, while 53.2% of nontornadic convective wind fatalities were unwarned. Most unwarned tornado fatalities occurred prior to the mid-1990's, coinciding with modernization of the National Weather Service while unwarned nontornadic convective wind fatalities remained at a relatively elevated frequency throughout the study period. Since 1999, 97% of unwarned tornado fatalities were associated with the first tornado of the day or outbreak days with seven or more tornadoes. Geographic locations with high numbers of unwarned tornado and nontornadic convective wind fatalities were associated with one high magnitude event that was unwarned rather than a series of smaller unwarned events over the period. There are many factors that contribute to warning response by the public and the issuance of a severe thunderstorm or tornado warning is an important initial step in the warning process. A better understanding of the characteristics of warned and unwarned fatalities is important to future reduction of unwarned fatalities.
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Schoen, J., and W. S. Ashley, 2011: A climatology of fatal convective wind events by storm type. Weather and Forecasting, 26, 109-121.

There are still hundreds of casualties produced by thunderstorm hazards each year in the United States despite the many recent advances in prediction and mitigation of the effects of convective storms. Of the four most common thunderstorm hazards (wind, hail, flooding, and lightning), convective winds (tornadic and nontornadic) remain one of the most dangerous threats to life and property. Using thunderstorm fatality and Weather Surveillance Radar-1988 Doppler (WSR-88D) data, this research illustrates a spatial and temporal analysis of the storm morphological characteristics, or convective mode, of all fatal tornadic and nontornadic convective wind events from 1998 to 2007. The investigation employs a radar-based morphology classification system that delineates storm type based on an organizational continuum, including unorganized cellular, quasi-organized cellular (either a cluster of cells or a broken line of cells), organized cellular (supercells and supercells embedded in an organized linear system), and organized linear (either squall lines or bow echoes). Results illustrate that over 90% of the 634 recorded tornado deaths were associated with supercells, with 78% of the deaths due to isolated tornadic supercells and 12% linked to tornadic supercells embedded within an organized linear convective system. The morphologies responsible for the 191 nontornadic convective wind fatalities vary substantially, with bow echoes (24%), squall lines (19%), and clusters of cells (19%) the most prominent convective modes producing fatalities. Unorganized and quasi-organized convection accounted for nearly half (45%) of all nontornadic convective wind fatalities. Over half of all fatal tornadoes (53%) occurred between 0000 and 0600 UTC, and most (59%) fatalities from nontornadic convective winds occurred in the afternoon between 1800 and 0000 UTC. Two corridors of nontornadic convective wind fatalities were present: the lower Great Lakes region and the mid-South. Tornado fatalities were greatest in a zone extending from southeastern Missouri, through western Tennessee, northeastern Arkansas, Mississippi, Alabama, and Georgia. The methods employed and results found in this study are directly applicable in the further development of storm classification schemes and provide forecasters and emergency managers with information to assist in the creation and implementation of new convective wind mitigation strategies.
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 Spencer, J. M., and W. S. Ashley, 2011: Avalanche fatalities in the western United States: A comparison of three databases. Natural Hazards, doi: 10.1007/s11069-010-9641-3.

Abstract
Reported avalanche fatalities in the United States increased markedly through the latter half of the twentieth century, a result of the increasing popularity of winter sports. Despite this increase, the literature concerning US avalanche fatalities is sparse. This paper presents a comparison of three US databases containing avalanche fatality information: Storm Data, the West Wide Avalanche Network (WWAN) dataset, and the National Avalanche Database (NAD). The frequency of avalanche fatalities, their temporal trends, spatial distributions, and the demographic characteristics of the victims were analyzed in each database for the years 1998–2009 for the US mountainous west. The data were then pooled to arrive at an estimate of avalanche fatality frequency in the United States for the study period. While the results indicate a considerable amount of overlap between the datasets, Storm Data reports fewer avalanche fatalities than both the WWAN and NAD datasets. All three datasets report a maximum of fatalities in January and display three spatial maxima: the Rocky Mountains of west-central Colorado, the intermountain region from central Utah through Idaho to west-central Montana, and the northern Cascade Ranges of Washington; however, a large void appears in the Storm Data records in the vicinity of the Montana maximum. These maxima result from a juxtaposition of avalanche hazard in these mountainous environments with a high concentration of winter sports activities.
http://www.springerlink.com/content/h824177u2h522028/
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Paulikas, M. J., and W. S. Ashley, 2011: Thunderstorm hazard vulnerability for the Atlanta, Georgia metropolitan region. Natural Hazards, doi: 10.1007/s11069-010-9712-5.

Abstract
Most U.S. metropolitan regions have experienced urban “sprawl,” or the outward spreading of urban development from city centers. For cities lying in areas prone to severe weather, the sprawl phenomenon exposes greater numbers of developed areas and inhabitants to a variety of thunderstorm hazards. This study’s principal goal is to determine how urbanization growth patterns affect a region’s vulnerability to severe weather events. To assess how sprawl may impact vulnerability to tornadoes, hail, and convective wind events, an analysis examining potential loss may be utilized. This study employs two distinct approaches to examine how the Atlanta area’s rapid and extensive development during the latter half of the twentieth Century has affected its overall potential exposure to thunderstorm hazards. First, archived census data are used to estimate overall impacts from hypothetical significant tornado, nontornadic convective wind, and hail events occurring at different time periods throughout several locations in the Atlanta metropolitan region. Second, economic factors are integrated into the analysis, which assists in determining how these hypothetical severe event scenarios may have changed from a cost standpoint if they were to occur in 2006 as opposed to 1960.
http://www.springerlink.com/content/n832354853728434/
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Schoen, J., and W. S. Ashley, 2011: A climatology of fatal convective wind events by storm type. Weather and Forecasting, 26, 109-121.

Abstract
There are still hundreds of casualties produced by thunderstorm hazards each year in the U.S. despite the many recent advances in prediction and mitigation of the effects of convective storms. Of the four most common thunderstorm hazards (wind, hail, flooding, and lightning), convective winds (tornadic and nontornadic) remain one of the most dangerous threats to life and property. Using thunderstorm fatality and WSR-88D data, this research illustrates a spatial and temporal analysis of the storm morphological characteristics, or convective mode, of all fatal tornadic and nontornadic convective wind events from 1998–2007. The investigation employs a radar-based morphology classification system that delineates storm type based on an organizational continuum, including: unorganized cellular; quasi-organized cellular (either a cluster of cells or a broken line of cells); organized cellular (supercells and supercells embedded in an organized linear system); and organized linear (either squall lines or bow echoes). Results illustrate that over 90% of the 634 recorded tornado deaths were associated with supercells, with 78% of the deaths due to isolated tornadic supercells and 12% linked to tornadic supercells embedded within an organized linear convective system. The morphologies responsible for the 191 nontornadic convective wind fatalities vary substantially, with bow echoes (24%), squall lines (19%), and clusters of cells (19%) the most prominent convective modes producing fatalities. Unorganized and quasi-organized convection comprised of nearly half (45%) of all nontornadic convective wind fatalities. Over half of all fatal tornadoes (53%) occurred between 0000 and 0600 UTC, and most (59%) fatalities from nontornadic convective winds occurred in the afternoon between 1800 and 0000 UTC. Two corridors of nontornadic convective wind fatalities were present: the lower Great Lakes region and the Mid South. Tornado fatalities were greatest in a zone extending from southeastern Missouri, through western Tennessee, northeastern Arkansas, Mississippi, Alabama, and Georgia. The methods employed and results found in this study are directly applicable in the further development of storm classification schemes and provide forecasters and emergency managers with information to assist in the creation and implementation of new convective wind mitigation strategies.
http://journals.ametsoc.org/doi/abs/10.1175/2010WAF2222428.1
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Bentley, M. L., W. S. Ashley, and J. A. Stallins, 2010: Climatological radar delineation of urban convection for Atlanta, Georgia. International Journal of Climatology, 30, 1589-1594.

Abstract
The distribution of warm season (June through August) thunderstorm activity surrounding Atlanta, Georgia from 1997 to 2006 was determined utilizing composite reflectivity data obtained from the network of National Weather Service radars. The radar data, at 2 km and 5 min spatial and temporal resolutions, allows for high resolution analyses of urban convective trends when grid averaged over a 10-year period.
Maxima of medium- to high-reflectivity episodes were identified to the north of and within downtown Atlanta and immediately east of the primary urban expansion of the central business district (CBD). Additional enhanced, high-reflectivity areas are found in southern Fulton and Clayton counties, located south of downtown Atlanta. These regions are also collocated with high-density urban expansion south of the Atlanta CBD. The research presented is the most comprehensive spatial and temporal analysis of grid averaged composite reflectivity data for urban convection conducted to date. Copyright © 2009 Royal Meteorological Society
http://onlinelibrary.wiley.com/doi/10.1002/joc.2020/abstract
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Black, A. W., and W. S. Ashley, 2010: Nontornadic convective wind fatalities in the United States. Natural Hazards, 54, 355-366.

Abstract
A database was compiled for the period 1977–2007 to assess the threat to life in the conterminous United States from nontornadic convective wind events. This study reveals the number of fatalities from these wind storms, their causes, and their unique spatial distributions. Nontornadic convective wind fatalities occur most frequently outdoors, in vehicles including aircraft, or while boating. Fatalities are most common in the Great Lakes and Northeast, with fewer fatalities observed in the central United States despite the climatological peak in severe thunderstorms in this region. Differences in fatality locations between tornadoes and nontornadic convective wind events highlight the unique combination of physical and social vulnerabilities involved in these deaths. Understanding these vulnerabilities is important to future reduction of nontornadic convective wind fatalities.
http://www.springerlink.com/content/p32064n752762524/
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Gensini, V. A., and W. S. Ashley, 2010: An examination of rip current fatalities in the United States.  Natural Hazards, 54, 159-175.

Abstract
A study analyzes fatalities caused by rip currents in the conterminous United States for the period 1994–2007. Results include the frequency of fatalities from rip currents, their cause, and their unique spatial distributions. An analysis of historical hazard event data illustrate that, on average, 35 people reportedly die from rip currents each year in the United States. Also, similar to other hazard events where unique differences in gender vulnerability have been found, men are over six times more likely to fall victim to a deadly rip current than females. Rip current fatalities are most common in the southeastern United States, with a nonuniform spatial distribution along other Atlantic, Pacific, and Great Lakes coastlines. Physical vulnerabilities are suggested as the primary cause for the unique fatality distribution found. Temporally, summer season weekends are shown to have the more fatalities than any other time of the year. A classification scheme was developed to categorize synoptic-scale weather conditions present during deadly rip current events. More than 70% of all rip current fatalities are associated with onshore winds. Specifically, a rip current fatality is most likely when a surface high pressure system creates these onshore winds. The quality of the fatality reporting database available for researchers is also assessed.
http://www.springerlink.com/content/q16t26655t504232/

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Ashley, W. S., and C. W. Gilson, 2009:  A reassessment of U.S. lightning mortality. Bulletin of the American Meteorological Society, 90, 1501–1518.

"Lightning is a unique weather hazard when compared to other perils such as tornadoes, flash floods, and hurricanes since lightning itself does not constitute a criterion for a severe event according to National Weather Service guidelines. Indeed, the mitigation of lightning casualties is complex since lightning is often preceded by no formal warning and little informal warning, because of the unpredictability and random nature of a lightning strike. This investigation tallies and assesses the fatalities produced by lightning in the United States from 1959 to 2006 in order to reevaluate the specific vulnerabilities and impacts associated with this deadly hazard. The study is the first to assemble a comprehensive lightning fatality dataset for the United States using both governmental and nongovernmental data sources. As with previous studies that have examined data discrepancies at the state level, the comparisons between traditional data sources such as Storm Data and other alternative data sources reveal significant differences in fatality tallies for the years when analyses overlap.

Mortality data are gridded and mapped at a much finer resolution than previous studies in order to reveal the distinctive spatial distributions of lightning fatalities, which are a combination of both risk and human vulnerability. Although lightning is not a criterion for either tornado or severe thunderstorm warnings, we assess whether lightning fatalities during the 1994–2004 period occurred in conjunction with these types of warnings. These warning data, in addition to radar analyses from 1998 to 2006, illustrate that unorganized, nonsevere thunderstorms are the most likely storm morphology yielding killer lightning events."
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Hall, S.G., and W.S. Ashley, 2008:  The effects of urban sprawl on the vulnerability to a significant tornado impact in northeastern Illinois. Natural Hazards Review, 9, 209-219.

Abstract: A sprawling U.S. population continues to spread into the fringes of urban development placing both populations and property in areas that were once largely unoccupied. Population tallies, housing unit totals, and housing values for 1990 and 2000 are examined to determine the extent to which this growth has affected the tornado hazard in northeastern Illinois. The growing town of Plainfield, Ill., located southwest of Chicago, is examined to determine how vulnerability to a tornado impact has changed in the town since an F5 tornado stuck the community in 1990. The population and housing data indicate an increase of 8,629 persons and 3,058 housing units affected if the tornado were to have occurred in 2000 rather than 1990. Estimations of housing value affected by the Plainfield tornado indicate a 50% increase in 2000 compared with 1990 values. In addition to studying the impacts on Plainfield, four other scenarios are examined in suburban Chicago counties using the 1990 Plainfield tornado as a model for a potentially devastating strike. The large increase in total value of homes affected for each scenario highlights the overall increase in wealth throughout the study area, specifically along the urban fringe of development. The physical vulnerability throughout the study area has increased with the rise in population, but the most socially vulnerable areas appear to remain in the older urban centers.
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Ashley, W.S., A.J. Krmenec, and R. Schwantes, 2008:  Vulnerability due to nocturnal tornadoes. Weather and Forecasting, 23, 795-807. Poster 

This study investigates the human vulnerability caused by tornadoes that occurred between sunset and sunrise from 1880 to 2007. Nocturnal tornadoes are theorized to enhance vulnerability because they are difficult to spot and occur when the public tends to be asleep and in weak building structures. Results illustrate that the nocturnal tornado death rate over the past century has not shared the same pace of decline as those events transpiring during the daytime. From 1950 to 2005, a mere 27.3% of tornadoes were nocturnal, yet 39.3% of tornado fatalities and 42.1% of killer tornado events occurred at night. Tornadoes during the overnight period (local midnight to sunrise) are 2.5 times as likely to kill as those occurring during the daytime hours. It is argued that a core reason why the national tornado fatality toll has not continued to decrease in the past few decades is due to the vulnerability of these nocturnal events. This vulnerability to nocturnal tornadoes is magnified when other factors such as escalating mobile (or “manufactured”) home stock and an increasing and spreading population are realized. Unlike other structure types that show no robust demarcation between nocturnal and daytime fatalities, nearly 61% of fatalities in mobile homes take place at night revealing this housing stock’s distinct nocturnal tornado vulnerability. Further, spatial analysis illustrates that the American South’s high nocturnal tornado risk is an important factor leading to the region’s high fatality rate. The investigation emphasizes a potential break in the tornado warning dissemination system utilized currently in the United States.
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Ashley, S.T., and W.S. Ashley, 2008:  Flood fatalities in the United States. Journal of Applied Meteorology and Climatology, 47, 805-818.

This study compiles a nationwide database of flood fatalities for the contiguous United States from 1959 to 2005. Assembled data include the location of fatalities, age and gender of victims, activity and/or setting of fatalities, and the type of flood events responsible for each fatality report. Because of uncertainties in the number of flood deaths in Louisiana from Hurricane Katrina, these data are not included in the study. Analysis of these data reveals that a majority of fatalities are caused by flash floods. People between the ages of 10 and 29 and 60 yr of age are found to be more vulnerable to floods. Findings reveal that human behavior contributes to flood fatality occurrences. These results also suggest that future structural modifications of flood control designs (e.g., culverts and bridges) may not reduce the number of fatalitiesnationwide. Spatially, flood fatalities are distributed across the United States, with high-fatality regions observed along the northeast Interstate-95 corridor, the Ohio River valley, and near the Balcones Escarpment in south-central Texas. The unique distributions found are likely driven by both physical vulnerabilities for flooding as well as the social vulnerabilities.
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Ashley, S.T., and W.S. Ashley, 2008:  The storm morphology of deadly flooding events in the United States. International Journal of Climatology, 28, 493-503.

This study investigates the synoptic and mesoscale environments associated with deadly flooding events in the United States from 1996 to 2005. A manual environment classification scheme, which includes analyses of surface charts, 500 hPa maps, and composite radar data (where available), is utilized to ascertain the primary ascent mechanisms and storm types producing these fatal flood events. Of the ten classifications in the scheme, the two most dominant ascent mechanisms associated with deadly floods include frontal boundaries (45%) and tropical systems (22%). Findings illustrate that mesoscale convective systems were responsible for 36% of the total number of flood fatalities over the period. The ten classifications are spatially and temporally analysed in order to assess region-specific risks associated with deadly flooding events. Copyright  2007 Royal Meteorological Society
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Ashley, W.S., and A. Black, 2008:  Fatalities associated with nonconvective high-wind events in the United States. Journal of Applied Meteorology and Climatology, 47, 717-725.

A database was compiled for the period 1980–2005 to assess the threat to life in the conterminous United States from nonconvective high-wind events. This study reveals the number of fatalities from these wind storms, their cause, and their unique spatial distributions. While tornadoes continue to cause the most wind-related fatalities per year, nonconvective high winds (defined as phenomena such as downslope and gap winds, gradient winds, dust storms, and winds associated with midlatitude cyclones) have the potential to fatally injure more people than thunderstorm or hurricane winds. Nonconvective wind fatalities occur more frequently in vehicles or while boating. Fatalities are most common along the West Coast and Northeast in association with passing extratropical cyclones, with fewer fatalities observed in the central United States despite this region’s susceptibility for high-wind gusts. A combination of physical and social vulnerabilities is suggested as the cause for the unique fatality distribution found. More than 83% of all nonconvective wind fatalities are associated with the passage of extratropical cyclones.
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Ashley, W.S., 2007:  Spatial and temporal analysis of tornado fatalities in the United States: 1880-2005. Weather and Forecasting, 22, 1214-1228.

A dataset of killer tornadoes is compiled and analyzed spatially in order to assess region-specific vulnerabilities in the U.S. from 1880-2005.  Results reveal that most tornado fatalities occur in the lower-Arkansas, Tennessee, and lower-Mississippi River Valleys of the Southeastern U.S. – a region outside of traditional “Tornado Alley.”  Analysis of variables including tornado frequency, land cover, mobile home density, population density, and nocturnal tornado probabilities demonstrate that the relative maximum of fatalities in the Deep South and minimum in the Great Plains may be due to the unique juxtaposition of both physical and social vulnerabilities.  The spatial distribution of these killer tornadoes suggests that the above national average mobile home density in the Southeast may be a key reason for the fatality maximum found in this area.  A demographic analysis of fatalities during the latter part of the database record illustrates that the middle aged and elderly are at a much greater risk than younger people during these events.  Data issues discovered during this investigation reveal the need for a concerted effort to obtain critical information about how and where all casualties occur during future tornado and hazardous weather events.  These new, enhanced data, combined with results of spatially explicit studies exploring the human sociology and psychology of these hazardous events, could be utilized to improve future warning dissemination and mitigation techniques.
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Ashley, W.S, T.L. Mote, and M.L. Bentley, 2007:  An extensive episode of derecho-producing convective systems in the United States during May-June 1998: A multi-scale analysis and review.  Meteorological Applications, 14, 227-244.

A multi-scale analysis is presented on widespread and long-lived convectively generated windstorms, known as derechos. Analyses of the derecho-producing environments during 15 May–30 June 1998 indicate that this exceptional episode of derechos and derecho groupings (or series) was supported by ingredients (i.e. moisture, instability, and wind shear) that were supplied by the large-scale setting. In particular, the semi-stagnant subtropical ridge and associated capping inversion across the southern tier of the U.S. were important in supplying amplified moisture and instability to derecho-genesis regions through an underrunning process. Regions of preferred derecho formation appeared to correspond to shifts in the overall strength and position of the ridge, illustrating the importance of the ridge in focusing successive organized convection. Initiating mechanisms varied widely and were not restricted to warm-air advection regimes along quasi-stationary boundaries that forecasters often associate with warm-season derecho environments. In several cases, derecho-producing convective systems were generated by tropospheric features not consistent with common conceptual models of derecho environments such as closed lows and strong vorticity maxima. Further, three distinct series types were identified and classified based on their initiating mechanisms.
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Suckling, P. W., and W. S. Ashley, 2006: Spatial and temporal characteristics of tornado path direction. The Professional Geographer, 58, 20-38.

Common perception is that tornadoes travel in paths from the southwest quadrant of directions toward the northeast. This study examines path directions for 6,194 tornadoes that occurred in the eastern two-thirds of the United States during the twenty-three-year period1980-2002. At the national scale, nearly 70 percent of tornadoes included in the study propagated from the west, west-southwest, and southwest, with west-southwest being the highest frequency origin direction. Nevertheless, distinct seasonal and regional variations were found. In central and northern areas of the country, a more westerly or northwesterly path origin prevails during late spring and summer. The midtropospheric flow, convective typology, and synoptic patterns of tornado outbreaks are thought to contribute to the distributions observed in the climatology.
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Ashley, W.S., T.L. Mote, and M.L. Bentley, 2005: On the episodic nature of derecho-producing convective systems in the United States. International Journal of Climatology, 25, 1915-1932

Convectively generated windstorms occur over broad temporal and spatial scales; however, one of the larger-scale and most intense of these windstorms has been given the name 'derecho'. This study illustrates the tendency for derecho-producing mesoscale convective systems to group together across the United States - forming a derecho series. The derecho series is recognized as any succession of derechos that develop within a similar synoptic environment with no more than 72 h separating individual events. A derecho dataset for the period 1994-2003 was assembled to investigate the groupings of these extremely damaging convective wind events. Results indicate that over 62% of the derechos in the dataset were members of a derecho series. On average, nearly six series affected the United States annually. Most derecho series consisted of two or three events; though, 14 series during the period of record contained four or more events. Two separate series involved nine derechos within a period of nine days. Analyses reveal that derecho series largely frequent regions of the Midwest, Ohio Valley, and the south-central Great Plains during May, June, and July. Results suggest that once a derecho occurred during May, June, or July, there was a 58% chance that this event was the first of a series of two or more, and about a 46% chance that this was the first of a derecho series consisting of three or more events. The derecho series climatology reveals that forecasters in regions frequented by derechos should be prepared for the probable regeneration of a derecho-producing convective system after an initial event occurs.
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Ashley, W.S., and T.L. Mote, 2005: Derecho Hazards in the United States.

Convectively generated wind-storms occur over broad temporal and spatial scales; however, the more widespread and longer lived of these windstorms have been given the name “derecho.” Utilizing an integrated derecho database, including 377 events from 1986 to 2003, this investigation reveals the amount of insured property losses, fatalities, and injuries associated with these windstorms in the United States. Individual derechos have been responsible for up to 8 fatalities, 204 injuries, forest blow-downs affecting over 3,000 km2 of timber, and estimated insured losses of nearly a $500 million. Findings illustrate that derecho fatalities occur more frequently in vehicles or while boating, while injuries are more likely to happen in vehicles or mobile homes. Both fatalities and injuries are most common outside the region with the highest derecho frequency. An underlying synthesis of both physical and social vulnerabilities is suggested as the cause of the unexpected casualty distribution. In addition, casualty statistics and damage estimates from hurricanes and tornadoes are contrasted with those from derechos to emphasize that derechos can be as hazardous as many tornadoes and hurricanes.
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Ashley, W.S., T.L. Mote, P.G. Dixon, S.L. Trotter, J.D. Durkee, E.J. Powell, and A.J. Grundstein, 2003: Distribution of mesoscale convective complex rainfall in the United States. Monthly Weather Review, 131, 12, 3003-3017.

Several annual mesoscale convective complex (MCC) summaries have been compiled since Maddox strictly defined their criteria in 1980. These previous studies have largely been independent of each other and therefore have not established the extended spatial and temporal patterns associated with these large, quasi-circular, and, typically, severe convective systems. This deficiency is primarily due to the difficulty of archiving enough satellite imagery to accurately record each MCC based on Maddox's criteria. Consequently, this study utilizes results from each of the MCC summaries compiled between 1978 and 1999 for the United States in order to develop a more complete climatology, or description of long-term means and interannual variation, of these storms. Within the 22-yr period, MCC summaries were compiled for a total of 15 yr. These 15 yr of MCC data are employed to establish estimated tracks for all MCCs documented and, thereafter, are utilized to determine MCC populations on a monthly, seasonal, annual, and multiyear basis. Subsequent to developing an extended climatology of MCCs, the study ascertains the spatial and temporal patterns of MCC rainfall and determines the precipitation contributions made by MCCs over the central and eastern United States. Results indicate that during the warm season, significant portions of the Great Plains receive, on average, between 8% and 18% of their total precipitation from MCC rainfall. However, there is large yearly and even monthly variability in the location and frequency of MCC events that leads to highly variable
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Presentations : Invited Talks - Papers Presented at Professional Meetings

Invited Talks

Ashley, W., and S. Talbot, 10 March 2012: Time-lapse photography of storm-scale features. Advanced Severe Weather Seminar, DuPage County Office of Homeland Security and Emergency Management, Naperville, IL.

Sirvatka, P., G. Izzi, and W. S. Ashley, 2011: Severe Weather Warning Debate. College of DuPage American Meteorological Society Debate, Glen Ellyn, IL

Ashley, W. S., 2011: Human vulnerability to severe convective storms. Indiana Integrated Warning Team Workshop, National Weather Service and Indiana Emergency Management Agency, Indianapolis, IN.

Ashley, W. S., 2 November 2010: Do cities enhance thunderstorm formation and intensity? Evidence from a Southeast U.S. warm-season radar climatology. Joint Chicago-NIU AMS Chapter Meeting, Lewis University, Romeoville, IL

Ashley, W. S., 23 October 2010: Storm Chasing. Invited talk part of NIU STEMFest. DeKalb, IL

Ashley, W. S., and M.L. Bentley, 1 October 2010: Urban- Induced Thunderstorm Modification in the Southeast United States. NIU Department of Geography Colloquium. DeKalb, IL.

Ashley, W. S., 24 August 2010: Human vulnerability to convection. 2010 Central and Eastern Iowa Integrated Warning Team Workshop, Cedar Rapids, IA.

Ashley, W. S., 25 April 2009: Tornadoes: Fatalities associated with nature’s most intense windstorm. Tom Skilling's 2009 Tornado and Severe Weather Seminar, Fermi National Accelerator Laboratory, IL.

Ashley, W. S., 17 April 2009: Weather-related mortality: Where, how, and what now? Kent State University, Kent, OH. Poster

Ashley, W. S., 3 March 2009: Human vulnerability to convection. Spring Severe Weather Workshop. National Weather Service Forecast Office, Romeoville, IL.

Ashley, W. S., 11 February 2009: U.S. lightning mortality. NIU Notables, DeKalb, IL.

Ashley, W. S., 18 November 2008: Weather-related mortality: Where, how, and what now? University of Nebraska-Lincoln, Lincoln, NE.

Ashley, W. S., 2008: Tornadoes: Fatalities associated with nature’s most intense windstorm. Invited talk for NIU Notables, DeKalb, IL.

Ashley, W. S., and A. Black, 2007: Tornadoes: Fatalities associated with nature’s most intense windstorm (with a little nonconvective spice thrown in). Invited talk at Joint Chicago-NIU AMS Chapter Meeting, DeKalb, IL.

Ashley, W. S., 2007: Tornadoes: Fatalities associated with nature’s most intense windstorm. Invited talk at Moraine Valley Community College, Palos Hills, IL.

Ashley, W. S., 2007: Derechos and tornadoes: Fatalities associated with Nature’s most intense windstorms. Invited talk to College of DuPage, Glen Ellyn, IL.

Ashley, W. S., 2006: Disaster preparedness: From the national to the local scale. NIU Dept. of Geography Brown Bag Seminar, DeKalb, IL.

Ashley, W. S., 2006: Derechos and tornadoes: Fatalities associated with Nature’s most intense windstorms. Invited talk to California University-Pennsylvania, California, PA.

Ashley, W. S., D. Changnon, R. Greene, and M. Bentley, 2005: Hurricane Katrina and the human migration aftermath. NIU Dept. of Geography Brown Bag Seminar, DeKalb, IL.

Ashley, W. S., 2005: Hazards of derecho-producing convective systems in the United States. Joint Chicago-NIU AMS Meeting, DeKalb, IL.

Ashley, W. S., 2005: Climatology and hazards of derecho-producing convective systems in the United States.  University of West Florida, Pensacola, FL.

Ashley, W. S., 2005: Climatology and hazards of derecho-producing convective systems in the United States.  Southern Illinois University, Carbondale, IL.

Ashley, W. S., 2005: Hazards of derecho-producing convective systems in the United States.  Northern Illinois University, DeKalb, IL.

Ashley, W. S., 2004: Climatology and hazards of derecho-producing convective systems in the United States. University of Wyoming, Laramie, WY.

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Papers Presented at Professional Meetings

Strader, Stephen M., and W.S. Ashley, 2012: Lightning signatures of long-lived tornadic supercells on 27-28 April 2011. 16th Severe Storms and Doppler Radar Conference, Akeney, IA.

Dixon, P. Grady, A.E. Mercer, and W.S. Ashley, 2012: Assessing Vulnerability to Tornado-Related Fatalities in the United States. 92nd American Meteorological Society Annual Meeting, New Orleans, LA.

Ashley, W.S., A. Osborne, and S. Ashley, 2012: Spatiotemporal analysis of thunderstorm hazard mortality rates.  92nd American Meteorological Society Annual Meeting, New Orleans, LA.

Stallins, T., J. Mulholland, M. Bentley, and W.S. Ashley, 2012: Weekend-weekday aerosol variability and patterns of cloud-to-ground lightning for Atlanta, Georgia (USA). The International Association for Urban Climate (IAUC) Eighth International Conference, Dublin, Ireland.

Bentley, M., W.S. Ashley, and T. Stallins, 2012: A weekend-weekday cloud-to-ground lightning climatology for an urban region in the southeastern U.S. Int. Geographical Congress, Cologne.

Dixon, P.G., A. Mercer, and W.S. Ashley, 2011: Tornado vulnerability of metropolitan areas in the United States. International Conference on Biometeorology, New Zealand.

Bentley, M. L., W.S. Ashley, and J.A. Stallins, 2011: Radar Identification of Urban-Enhanced Thunderstorm Activity for Atlanta, Georgia, USA. Joint Urban Remote Sensing Event, Geoscience and Remote Sensing Society, Munich, Germany.

Briley, L., W.S. Ashley, R. Rood, and A. Krmenec, 2011: An Evaluation of CMIP3 Precipitation Projections for the Great Lakes. West Lakes AAG, Chicago, IL.

Ashley, W.S., A. Osborne, and R. Sengenberger, 2011: Normalized mortality rates for thunderstorm hazards.  15th Annual NWA Severe Storms and Doppler Radar Conference, Ankeny, IA.

Ashley, W. S., M. L. Bentley, and T. Stallins, 2011: Urban Augmentation of Thunderstorm Frequency and Severity. 107th Annual Association of American Geographers Meeting, Seattle, WA.

Ashley, W. S. , M. L. Bentley, and T. Stallins, 2010: Do cities encourage thunderstorm formation and intensification? 25th Conference on Severe Local Storms, Denver, CO.

Gensini, V., and W. S. Ashley, 2010: Climatology of potentially severe convective environments from reanalysis. 25th Conference on Severe Local Storms, Denver, CO.

Bentley, M. L., Ashley, W. S. and J. A. Stallins, 2010: A climatology of urban augmented thunderstorms for cities in the Southeastern U.S. Western Pacific Geophysics Meeting, American Geophysical Union, Taipei, Taiwan.

Ashley, W. S., M. L. Bentley, and T. Stallins, 2010: Do cities encourage thunderstorm formation and intensification? The case of Atlanta, GA. 14th Annual NWA Severe Storms and Doppler Radar Conference, West Des Moines, IA.

Ashley, W. A., M. L. Bentley, and T. Stallins, 2010: Radar and lightning delineation of urban-enhanced thunderstorms for Atlanta, Georgia. 22nd Conference on Climate Variability and Change, 90th AMS Meeting, Atlanta, GA. Poster

Bentley, M. L. , and W. S. Ashley, and T Stallins, 2009. Radar delineation of urban-enhanced thunderstorms for cities in the southeastern U.S. 7th International Conference on Urban Climatology, Tokyo, Japan.
        
Spencer, J., and W. S. Ashley, 2009: Winter weather fatalities in the coterminous United States: 1993-2007.  Illinois GIS Association 2009 Spring Conference. University if Illinois, Champaign, IL.

Gilson, C.W., W. S. Ashley, M. L. Bentley, and J. Stallins, 2009: Human vulnerability to lightning in Georgia. 13th Annual Severe Storm and Doppler Radar Conference, West Des Moines, IA.

Schoen, J., and W. S. Ashley, 2009: Storm morphology of fatal convective straight-line wind events. 13th Annual Severe Storm and Doppler Radar Conference, West Des Moines, IA.

Ashley, W. S., M.L. Bentley, and J.A. Stallins, 2009: Radar-based climatology of urban heat island enhanced convection in the Southeast U.S.: The case of Atlanta, GA. 105th Annual Association of American Geographers Meeting, Las Vegas, NV.

Ashley, W. S., A. J. Krmenec, and R. Schwantes, 2008: Vulnerability due to nocturnal tornadoes. 24th Annual Severe Local Storms Conference, Savannah, GA. Poster 

Black, A., and W. S. Ashley, 2008: Non-tornadic convective wind fatalities in the U.S. 24th Annual Severe Local Storms Conference, Savannah, GA.

Ashley, W. S., C. Gilson, and D. Keith, 2008: A reassessment of lightning fatalities in the United States: Analyses of contrasting datasets, spatial distributions, and storm morphologies. 17th on Applied Climatology, Whistler, B.C., Canada.

Ashley, W. S., 2008: Lightning fatalities in the United States: An assessment of risk and vulnerabilities. 104th Annual Association of American Geographers Meeting, Boston, MA.

Ashley, W. S., A. J. Krmenec, and R. Schwantes, 2008: Vulnerability due to nocturnal tornadoes. 12th Annual Severe Storm and Doppler Radar Conference, West Des Moines, IA. Poster

Ashley, W. S., and C. Gilson, 2008: A reassessment of lightning fatalities in the United States. 12th Annual Severe Storm and Doppler Radar Conference, West Des Moines, IA.

Ashley, W. S., and S. T. Ashley, 2007: The relationship between flash flood warnings and fatalities. 32nd Annual National Weather Association Meeting, Reno, NV. Poster

Ashley, W. S., 2007:  The geography of tornado fatalities in the United States. The 103rd Annual Association of American Geographers Meeting, San Francisco, CA.

Ashley, S. T., and W. S. Ashley, 2007: The relationship between flash flood warnings and fatalities. 11th Annual Severe Storm and Doppler Radar Conference, West Des Moines, IA. Poster

Black, A., and W. S. Ashley, 2007: Fatalities associated with non-convective high wind events in the U.S. 11th Annual Severe Storm and Doppler Radar Conference, West Des Moines, IA.

Ashley, W. S., 2007:  Spatial and temporal analysis of tornado fatalities in the U.S. 11th Annual Severe Storm and Doppler Radar Conference, West Des Moines, IA. Poster

Ashley, W. S., 2006:  Spatial and temporal analysis of tornado fatalities in the U.S. 23rd Annual Conference on Severe Local Storms, St. Louis, MO, American Meteorological Society. Poster

Black, A., and W. S. Ashley, 2006:  Fatalities associated with non-convective high wind events in the United States. 23rd Annual Conference on Severe Local Storms, St. Louis, MO, American Meteorological Society.

Ashley, W. S., 2006:  Windstorm casualties in the United States: An assessment of vulnerabilities 10th Annual Severe Storm and Doppler Radar Conference, Des Moines, IA.

Ashley, W. S., 2006:  Windstorm-induced casualties in the United States. The 102nd Annual Association of American Geographers Meeting, Chicago, IL.

Suckling, P. W., and W. S. Ashley, 2006:  Spatial and temporal characteristics of tornado path direction. The 102nd Annual Association of American Geographers Meeting, Chicago, IL.

Ashley, W. S., 2005:  Derecho families: designation, climatology, and environments. The 101st   Annual Association of American Geographers Meeting, Denver, CO.

Ashley, W. S., 2004:  Derecho casualties in the United States.  2004 Annual Meeting of the Southeastern Division of the Association of American Geographers, Biloxi, MS.

Ashley, W. S., 2004:  Derecho hazards in the United States. The 100th Annual Association of American Geographers Meeting, Philadelphia, PA.

Wassel, G. A., W. S. Ashley, T. L. Mote, and M. L. Bentley, 2004:  On the episodic nature of long-lived, convectively generated high-wind events in the United States. The 100th Annual Association of American Geographers Meeting, Philadelphia, PA.

Ashley, W. S., M. L. Bentley, T. L. Mote, and J. L. Dyer, 2003:  A preliminary investigation into derecho families. 28th Annual Meeting of the National Weather Association, Jacksonville, FL.

Durkee, J. D., T. L. Mote, W. S. Ashley, and J. L. Dyer, 2003:  The precipitation efficiency of warm-season mesoscale convective complexes in the United States. 28th Annual Meeting of the National Weather Association, Jacksonville, FL.

Ashley, W. S., P. G. Dixon, J. D. Durkee, E. J. Powell, and S. L. Trotter, 2003:  A hydroclimatology of mesoscale convective complexes in the United States. The 99th Annual Association of American Geographers Meeting, New Orleans, LA.

Dixon, P. G., W. S. Ashley, J. D. Durkee, E. J. Powell, S. L. Trotter, T. L. Mote, and A. J. Grundstein, 2002: Precipitation contributions of mesoscale convective complexes in the southeastern United States. 1st Annual Southeast Severe Storms Symposium, Mississippi State, MS.

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