Research
Publications
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
Publications:
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 period 1980-2002. 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. Bulletin of the American Meteorological Society, 86, 1577-1592.
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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