Kenneth F. Dewey

Global Snow Cover Monitoring: An Update

Abstract Accurate monitoring of the large-scale dimensions of global snow cover is essential for understanding details of climate dynamics and climate change. Presently, such information is gathered individually from ground station networks and satellite platforms. Efforts are in progress to consolidate and analyze long-term station records from a number of countries. To gain truly global coverage, however, satellite-based monitoring techniques must be employed. A 27-year record of Northern Hemisphere continental snow cover produced by the National Oceanic and Atmospheric Administration (NOAA) is the longest such environmental record available. Records of Southern Hemisphere continental cover and snow on top of Arctic sea ice have been produced by similar means for a portion of this interval. The visible imagery charting technique used to generate these data provides information on snow extent but not on snow volume. Satellite microwave analyses over Northern Hemisphere lands show some promise in this reg...

A Digital Archive of Northern Hemisphere Snow Cover, November 1966 through December 1980

The purpose of this article is to acquaint the research community with a new data base—a digitized archive of Northern Hemisphere snow cover. Historically, those researchers who needed snow cover data for climatic and atmospheric boundary layer studies have had to rely on the irregularly spaced (and in some regions, sparse) grid of point observations. Northern Hemisphere Weekly Snow and Ice Cover Charts, which are created from analyzed satellite imagery at the National Earth Satellite Service (NESS), have been available on an operational basis since late 1966. Each of these weekly charts for the period November 1966 through December 1980 was digitized and stored in a new data archive. Snow cover area and snow cover frequency climatologies were created and examples are presented. The significance of this unique data archive is examined by comparing the 14-year mean annual snow cover frequency climatology with several published snow cover climatologies. The potential uses for this data archive in meteorolog...

CIRCULATION PATTERNS AND TEMPERATURE FIELDS ASSOCIATED WITH EXTENSIVE SNOW COVER ON THE NORTH AMERICAN CONTINENT

Weekly snow cover areas, derived from the NOAA/NESS Northern Hemisphere Digitized Snow and Ice Cover Data Base, were correlated with weekly temperature anomalies across the United States and with weekly 700-mb geopotential heights over the North American sector. The correlations were computed for snow cover across the entire North American continent as well as the western and eastern United States for the winters 1966–67 through 1979–80. Extensive snow cover is associated with negative temperature anomalies across most of the continental United States. The strongest relationship occurs along the eastern flank of the Rocky Mountains from the Canadian border to the central Great Plains and reflects the southward movement of cold arctic air masses toward the Gulf of Mexico. An anomalous trough over the western part of North America is responsible for extensive snow cover in the winter. The surface storm track is displaced southward during winters with heavy snow cover, with cyclones occurring more frequently...

A Climatology of Mean Monthly Snowfall for the Conterminous United States: Temporal and Spatial Patterns

Abstract Mean monthly snowfall data for 216 stations across the conterminous United States were analyzed to produce a climatology that identifies statistical, spatial and intraseasonal aspects. Geographic variations in the length of the snowfall season are characterized using two statistics: the number of months of snow and the Snow Concentration Index (SCI). The annual distribution of mean monthly snowfall is also examined using harmonic analysis. Snowfall across the conterminous United States generally peaks in February; earlier snowfall maxima are found in the Great Lakes area and in the Pacific Northwest, whereas late February or March maxima occur in the western High Plains. Stations with relatively high amounts of variance explained by the second harmonic indicate 1) areas with a short snowfall season such as the southeastern United States, or 2) areas with a long snowfall season that have a tendency toward a bimodal distribution. A climatology of the changing monthly patterns of snowfall is identif...

Satellite-Derived Maps of Snow Cover Frequency for the Northern Hemisphere

Abstract A satellite imagery-based Northern Hemisphere snow cover data archive was mapped for the period 1966–84: The maps were digitized in order to create the first hemispheric, spatially data-continuous climatologies of snow cover. Annual and monthly climatologies were created and compared to several standard or frequently referenced climatologies. Results of this analysis indicate that the satellite-based climatology provides a much more detailed climatology for the higher latitude and highland regions of the Northern Hemisphere. The satellite imagery-based maps, when compared to the historical snow cover climatologies, indicated more extensive high-latitude snow cover concurrent with a northward shift in the southern extent of the climatological snow cover, this results in a narrower snow-transition zone.

A Preliminary Investigation of a Relationship between South American Snow Cover and the Southern Oscillation

Abstract A ten-year (1974–83) satellite record of snow cover is compared to a standard index of the Southern Oscillation. South American snow cover area during the May-October snow mean is found to be correlated significantly with the winter SOI values of the same year. The relationship is inverse; periods of low SOI values are associated with extensive South American snow cover while periods of high SOI values occur during years of diminished snow cover. The movements of the Pacific anticyclone and the midlatitude westerlies and subsequent changes in precipitation and temperature patterns are discussed in an analysis of this relationship.

Some observations on climate variability as seen in daily temperature structure

Abstract Distinctive annual cycles of daily maximum and minimum temperature and temperature range are observed across the United States when averaging daily data for multiple decades. In some cases, abrupt changes in the range between daily maximum and minimum temperatures are observed within annual cycles. Such discontinuities, or steps, of 5°C may occur within a week, despite the fact that the daily data are averaged over several decades. Discontinuities are most pronounced in the fall and spring, and display differing characteristics of timing, rapidity, magnitude and direction of change across the nation. In northern and central portions of the eastern U.S., a winter minimum and summer maximum in temperature range is observed, while in the southern U.S. the opposite is found. Abrupt discontinuities are observed in early November in the Northeast and in late spring and early summer in the Southeast and Southwest. Differences in mean daily temperature cycles between various portions of this century are a function of variations in maximum and minimum temperatures. The central U.S. had higher maximum and minimum temperatures during the 1930s than at other times this century, with little affect on daily temperature range. In the Northeast, the temperature range was lower in the 1930s, as a result of decreased maximum and increased minimum temperatures. The dynamics responsible for changes within the annual cycle or between different periods have not yet been unequivocally identified. The location of the polar front jet stream and its associations with solar radiation, clouds, snow cover and other atmospheric and surface variables are certainly involved. We believe that the identification of the climate system dynamics responsible for the structure of the annual cycle of daily temperature is a necessary first step in the study of potential human-induced climate change.

The Prediction of Lake Huron Lake-Effect Snowfall Systems

Abstract Data were collected during the 1971–72 snowfall season for the Lake Huron basin. The bulk aerodynamic approach, as formulated by Priestley, was utilized to estimate the daily average flux of heat and moisture over the lake. It was hypothesized that discriminant analysis could be employed to determine the threshold value (discriminant index) of the energy flux which is necessary for the occurrence of the lake-effect snowfall system. To determine the validity of this threshold value, the discriminant index was applied to a series of historical data. The results of this analysis indicated that the discriminant index could be utilized to forecast lake-effect snowfall days.