Daniel J. Leathers

The Pacific/North American Teleconnection Pattern and United States Climate. Part I: Regional Temperature and Precipitation Associations

An electrical circuit for limiting surge currents through incandescent indicator or display lamps is disclosed. It is essentially a constant current device having a current controlling transistor in the load circuit to limit the initial surge current to a first value after, which the lamp itself limits the current. Provision is made for testing of the lamp and circuit by maintenance personnel.

The Pacific/North American Teleconnection Pattern and United States Climate. Part II: Temporal Characteristics and Index Specification

Abstract The PNA teleconnection index, a measure of the strength and phase of the Pacific/North American teleconnection pattern, is used to examine changes in the midtropospheric flow over North America on decadal, interannual, and intra-annual time scales. The index corroborates previous findings that a major change in the midtropospheric circulation took place over North America during the late 1950s. The time series of index values also demonstrates the existence of a previously unknown quasi periodicity in the configuration of midtropospheric heights over the North American sector. A seasonal specification analysis is conducted to identify climate system components that are closely linked to the PNA teleconnection. The selection of predictor variables is based on recent modeling and observational work suggesting their probable involvement with midiatitude flow variations. These include sea surface temperatures for locations in the tropical Pacific and North Pacific, along with Asian land surface tempe...

The Association between Extremes in North American Snow Cover Extent and United States Temperatures

Abstract The association between satellite-derived North American snow cover extent and United States winter (December, January, February) temperature is examined. The results indicate that winter months evidencing extreme positive (negative) values of North American snow cover extent are associated with below- (above) normal temperatures across the majority of the United States. The area evidencing the largest temperature departures during both positive and negative North American snow cover extremes is located across the central United States, roughly from the Dakotas south through the southern plains, and from the Rocky Mountains east to the Mississippi Valley. This area is collocated with the largest variations in snow cover frequency. No consistently strong association is indicated east of the Appalachians or west of the Rocky Mountains. During December, strong 500-mb height anomalies are collocated with the area of maximum snow cover frequency deviations and the largest temperature departures. This ...

The Severe Flooding Event of January 1996 across North-Central Pennsylvania

Abstract The rapid ablation of a snowpack and intense rainfall combined to cause catastrophic flooding across much of the mid-Atlantic region of the United States on 18 and 19 January 1996. This flooding event resulted in as many as 30 fatalities, numerous injuries, and damage estimated at

SYNOPTIC MECHANISMS ASSOCIATED WITH SNOWFALL INCREASES TO THE LEE OF LAKES ERIE AND ONTARIO

1.5 billion. The Loyalsock and Lycoming Creek watersheds in northern Pennsylvania were arguably the hardest hit areas in the region, at least from the perspective of fatalities and injuries. This flooding event, which was certainly devastating from a human and economic perspective, also represents an interesting scientific situation in which climatological preconditioning and the occurrence of an unusual synoptic-scale weather event combined to create disastrous results. Before the event, snow fell at record levels across northern Pennsylvania during the late autumn and early winter seasons. By the middle of January 1996, more snow had fallen across the combined watershed region than is expected during an average snowf...

Analysis of Cold Airmass Temperature Modification across the U.S. Great Plains as a Consequence of Snow Depth and Albedo

Snowfall is a cyrospheric variable that impacts nearly every sector of society. Because of its societal importance, snowfall is a logical variable to be used as an indicator of potential global environmental change. This study investigates the mechanisms responsible for large observed snowfall increases across the eastern Great Lakes region of the USA. Results indicate that mean snowfall amounts across sections of western New York and north-western Pennsylvania have increased by up to 100 cm over the 60-year period encompassing the snowfall seasons 1930–1931 through to 1989–1990. A synoptic climatological approach is utilized to identify consistent synoptic-scale atmospheric patterns responsible for snowfall across the region. Nine synoptic types are identified as producing significan t snowfall in the study area; five with synoptic characteristics indicative of lake-effect snowfall and four evidencing characteristics of snowfall associated with cyclonic influence. An examination of the seasonal frequency of the nine synoptic types indicates a substantial increase in the frequency of the five lake-effect synoptic types and a long-term decrease in the numbers of cyclone synoptic types over the period 1950–1951 through to 1981–1982. Information concerning trends in the frequency and the intensity of each of the nine snowfall-producing synoptic types was combined to produce a modelled snowfall change due to frequency and intensity variations over the period. Trends in the frequency and intensity of the synoptic patterns associated with lake- effect snowfall explain the majority of the observed snowfall increase across the region. Variations in the synoptic types associated with cyclonically induced snowfall are shown to be unimportant to snowfall changes across the eastern Great Lakes area. Possible reasons for increases in the frequency and the intensity of the lake-effect synoptic types are discussed.

Snowmelt-Related Flood Risk in Appalachia: First Estimates from a Historical Snow Climatology

Abstract The presence of snow cover has been shown to modify atmospheric conditions through much of the earth’s troposphere due to its radiative effects. Snow cover has garnered much attention in recent decades as a result of concerns associated with potential changes in the global environment that may be intensified by the presence or absence of a snow cover. As a result, a greater emphasis has been placed on the representation of snow cover in weather and climate prediction models. This study investigates the effects of snow albedo and snow depth on the modification of surface air temperatures within cold air masses moving across the U.S. Great Plains in winter. Through the adaptation of a one-dimensional snowpack model, the thermal characteristics of the core of a cold air mass were derived from the equation governing the heat balance between the surface and the lower atmosphere. The methodology was based on the premise that the core of a cold air mass may be considered homogeneous and not subject to a...

The effects of a discontinuous snow cover on lower atmospheric temperature and energy flux patterns

Abstract A first attempt has been made toward quantifying the risk of snowmelt-related flooding in the central and southern Appalachian Mountains of the United States (from 35° to 42°N). In the last decade, two major events occurred within the region, prompting this study. Snowfall and snow depth data were collected from the cooperative observer network, quality controlled, and summarized at seasonal resolution (December–March). For establishing regional patterns, the period of 1971–2000 was selected. For testing fits of candidate probability distributions, and for focusing on the sparsely sampled higher elevations, this criterion was relaxed to include as many data from the mid- to late century as were reasonably admissible. Results indicate that the two-parameter Gumbel distribution fit best both the seasonal total snowfall and seasonal maximum snow depth. That distribution was then used to map return periods associated with critical seasonal snowfall and maximum snow depth masses. Seasonal snowfall amo...

A Synoptic Climatological Approach to the Analysis of Lake-Effect Snowfall: Potential Forecasting Applications

Snow cover and its interaction with the earths troposphere has become a topic of increased interest over the past several decades. Studies have produced evidence of links between snow cover and precipitation patterns, temperature fields, and atmospheric circulation patterns. Few studies have investigated anomalous atmospheric temperature and circulation patterns over snow cover boundaries or patchy snow cover. This study provides analysis of model-derived lower atmospheric temperatures and contributing energy fluxes within a cold air mass positioned over discontinuous snow cover. Results of the analysis show that simulated air mass temperatures were 1–4°C cooler over a patch of snow cover than over surrounding bare ground during a midday hour. The temperature differences were primarily the result of variations in the magnitude and direction of the surface layer sensible heat flux, as produced by differences between the solar radiation absorbed by the snow cover and the surrounding bare ground.

Characteristics of snow cover duration across the northeast United States of America

Abstract Due to their mesoscale nature, forecasting lake-effect snowfall events is very difficult but extremely important to the inhabitants of those regions subject to this type of severe winter weather. Such is the case along the southern and eastern shores of Lakes Erie and Ontario in the northeastern region of the United States. Here a synoptic climatological approach is used to identify the synoptic-scale atmospheric patterns conductive to lake-induced snowfall to the lee of Lakes Erie and Ontario in the states of New York and Pennsylvania from November to March. The approach used in this study allows for a thorough investigation of the characteristics of each lake-effect synoptic type, including the intrannual and interannual variations in frequency and composite atmospheric fields of sea level pressures, 850-mb temperatures and heights, and 500-mb heights. By combining the lake-effect synoptic types with daily snowfall data for 159 stations across New York and Pennsylvania, direct associations are ...