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  • Author or Editor: James R. Angel x
  • Journal of Applied Meteorology and Climatology x
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James R. Angel
and
Floyd A. Huff

Abstract

The rainstorm on 17–18 July 1996 in northern Illinois produced three rainfall records. The 43.0-cm total storm rainfall at Aurora was the greatest point rainfall recorded for storm durations of 24 hours or less in this century in Illinois and most surrounding states. The 27.9-cm storm rainfall recorded in the southwestern part of the Chicago metropolitan area was the heaviest 24-h amount ever recorded in that city. The July 1996 storm also produced the heaviest 24-h mean rainfall recorded in Illinois over areas of 5200 and 13 000 km2 immediately surrounding the storm center.

An area of approximately 12 000 km2 experienced 24-h point rainfall amounts that exceeded those expected to occur, on the average, once in 10 years. Similarly, the 25-, 50-, and 100-yr frequency values were exceeded over areas of 6730, 4920, and 3500 km2, respectively.

One concern resulting from a major rainfall event such as this storm is its impact on the rainfall frequency analysis. This new information may result in changes in the estimated rainfall amounts at selected return periods, which are used to design water-handling structures. Based on previous research, the Aurora rainfall appears to exceed the 1000-yr return period. However, fitting a statistical distribution to the annual maximum time series and using regional averages minimized the effect of this storm on rainfall frequency estimates.

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Alan Marinaro
,
Steve Hilberg
,
David Changnon
, and
James R. Angel

Abstract

The severe 2013/14 winter (December–March) in the Midwest was dominated by a persistent atmospheric circulation pattern anchored to a North Pacific Ocean that was much warmer than average. Strong teleconnection magnitudes of the eastern Pacific oscillation (−EPO), tropical Northern Hemisphere pattern (+TNH), and second-lowest Hudson Bay 500-hPa geopotential height field are indicators that led to severe winter weather across the eastern United States. Unlike in previous cold and snowy midwestern winters, Atlantic Ocean blocking played little to no role in the winter of 2013/14. The primary atmospheric feature of the 2013/14 winter was the 500-hPa high pressure anchored over the North Pacific in response to the extremely warm sea surface temperature anomalies observed of +3.7 standard deviations. Only one other severe midwestern winter (1983/84) since 1950 featured a similar Pacific blocking. The accumulated winter season severity index, which is a metric that combines daily snowfall, snow depth, and temperature data for the winter season, was used to compare the 2013/14 winter with past winters since 1950. Detroit, Michigan, and Duluth, Minnesota, experienced their worst winter of the 55-yr period. Seven climate divisions in northern Illinois, eastern Iowa, and parts of Wisconsin experienced record-cold mean temperatures. These climate conditions were associated with a number of impacts, including a disruption to the U.S. economy, the second-highest ice coverage of the Great Lakes since 1973, and a flight-cancellation rate that had not been seen in 25 years.

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James R. Angel
,
Michael A. Palecki
, and
Steven E. Hollinger

Abstract

Soil erosion is a major global challenge. An increased understanding of the mechanisms driving soil erosion, especially the storms that produce it, is vital to reducing the impact on agriculture and the environment. The objective of this work was to study the spatial distribution and time trends of the soil erosion characteristics of storms, including the maximum 30-min precipitation intensity (I 30), storm kinetic energy of the falling precipitation (KE), and the storm erosivity index (EI) using a long-term 15-min precipitation database. This is the first time that such an extensive climatology of soil erosion characteristics of storms has been produced. The highest mean I 30, KE, and EI values occurred in all seasons in the southeastern United States, while the lowest occurred predominantly in the interior west. The lowest mean I 30, KE, and EI values typically occurred in winter, and the highest occurred in summer. The exception to this was along the West Coast where winter storms exhibited the largest mean KE and EI values. Linear regression was used to identify trends in mean storm erosion characteristics for nine U.S. zones over the 31-yr study period. The south-central United States showed increases for all three storm characteristics for all four seasons. On the other hand, higher elevations along the West Coast showed strong decreases in all three storm characteristics across all seasons. The primary agricultural region in the central United States showed significant increases in fall and winter mean EI when there is less vegetative cover. These results underscore the need to update the storm climatology that is related to soil erosion on a regular basis to reflect changes over time.

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Michael A. Palecki
,
James R. Angel
, and
Steven E. Hollinger

Abstract

Climate studies of precipitation have generally focused on daily or longer time scales of precipitation accumulation. The main objective of this work was to identify the precipitation characteristics of storms based on 15-min precipitation data, including storm total precipitation, storm duration, mean storm intensity, and maximum 15-min intensity. A group of precipitation characteristics was subjected to a cluster analysis that identified nine regions of the conterminous United States with homogeneous seasonal cycles of mean storm precipitation characteristics. Both mean and extreme statistics were derived for each characteristic and season for each zone. Continuous probability density functions were generated that appropriately fit the empirical distributions of storm total precipitation and maximum 15-min intensity. The storm characteristics, in turn, were a function of seasonal water availability from source regions, atmospheric water vapor capacity, and storm precipitation mechanism. This is the first time that such an extensive climatology of storm precipitation characteristics has been produced. A preliminary trend analysis of the 1972–2002 storm characteristic data by zone showed substantial changes that tended to be geographically coherent, with noteworthy differences between the western and eastern United States. The western United States displayed a trend toward decreasing storm total precipitation and storm duration in most seasons, while storm intensity increased. The eastern United States experienced a general pattern of increasing storm total precipitation and storm duration during winter, as well as a tendency for maximum 15-min precipitation intensity to increase.

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Karsten A. Shein
,
Dennis P. Todey
,
F. Adnan Akyuz
,
James R. Angel
,
Timothy M. Kearns
, and
James L. Zdrojewski

Abstract

The NOAA National Climatic Data Center maintains tables for temperature and precipitation extremes in each of the U.S. states. Many of these tables were several years out of date, however, and therefore did not include a number of recent record-setting meteorological observations. Furthermore, there was no formal process for ensuring the currency of the tables or evaluating observations that might tie or break a statewide climate record. This paper describes the evaluation and revision of the statewide climate-extremes tables for all-time maximum and minimum temperature, greatest 24-h precipitation and snowfall, and greatest snow depth (the five basic climate elements observed on a daily basis by the NOAA Cooperative Weather Network). The process resulted in the revision of 40% of the values listed in those tables and underscored both the necessity of manual quality-assurance methods and the importance of continued climate-monitoring and data-rescue activities to ensure that potential record values are not overlooked.

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