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Kenneth F. Dewey

Abstract

Research into the relationship between snow cover and observed maximum and minimum temperature is reviewed. An example of the importance of snow cover and forecasting max/min temperatures is presented for this past winter (1976–77). It is shown that there was a warm bias in the MOS temperature forecasts for the northern Great Plains following the receipt of a fresh cover of snowfall. It is proposed that snow cover be incorporated as a conditional predictor to be used only during specific synoptic conditions.

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Kenneth F. Dewey

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.

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Kenneth F. Dewey

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.

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Kenneth F. Dewey
and
Richard Heim Jr.

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 meteorological and climatological studies also are reviewed.

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Randall S. Cerveny
,
Brent R. Skeeter
, and
Kenneth F. Dewey

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.

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John A. Harrington Jr.
,
Randall S. Cerveny
, and
Kenneth F. Dewey

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 identified through the mapping of station deviations from a national composite. This procedure produces contiguous regions that can be related to seasonal changes in the extent and positioning of the circumpolar vortex. The maps reveal that positive snowfall deviations predominate 1) in autumn in the northern and western Great Plains and the Rocky Mountains (with a full-latitude trough over the central United States and associated upslope precipitation); 2) in early winter in the Great Lakes (associated with lake-effect storms); 3) in late winter over the southern and western states (with a fully expanded circumpolar vortex); and 4) in spring in the western states (linked to seasonal changes in preferred locations of cyclogenesis and associated storm tracks).

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David A. Robinson
,
Kenneth F. Dewey
, and
Richard R. Heim Jr.

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 regard, however, large-scale monitoring of snow extent with microwave data remains less accurate than visible charting.

This paper updates the status of global snow cover monitoring, concentrating on the weekly snow charts prepared by NOAA and discussing a new and consistent record of monthly snow cover generated from these weekly charts. The NOAA charts show a reduction of hemispheric snow cover over the past five years, particularly in spring. Snow areas from the NOAA product are then compared with values derived using passive microwave data. The latter consistently reports less snow cover than the more accurate visible product. Finally, future snow monitoring initiatives are recommended. These include continuing the consistent NOAA product until an all-weather all-surface product is developed. The latter would use multiple data sources and geographic information systems techniques. Such an integrative product would need extensive comparisons with the NOAA product to ensure the continued utility of the lengthy NOAA observations in studies of climate change. In a retrospective sense, satellite charts from the middle 1960s to early 1970s need reevaluation and techniques to merge satellite products with historic station time series must be developed.

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