CHARACTERISTICS OF TEMPERATURE DEPRESSIONS ASSOCIATED WITH SNOW COVER ACROSS THE NORTHEAST UNITED-STATES

Daily snow cover and temperature data are collected for a network of 91 stations covering the northeast United States and the association between the two is explored. Observations are examined for the six-month winter season, November-April, for the period 1948/49-1987/88. Daily maximum and minimum temperatures are stratified by 15-day periods and further by the presence or absence of a snow cover. It is found that for snow covers of 2.5 cm or greater, depressions of daily maximum and minimum temperature average approximately 6 degrees and 5 degrees C, respectively. Relatively large variations in the temperature depressions are observed across space, whereas smaller variability is found across the snow cover season. Temporally, maximum temperature depressions are greater during the early and later portions of the snow cover season and somewhat smaller during the midwinter months. The magnitude of minimum temperature depressions are larger during the midwinter months but decrease in size early and especially late in the snow cover season. The presence of a snow cover decreases the daily temperature range in November, March, and April and has little effect during the intervening months. Spatially, the magnitude of both maximum and minimum temperature depressions increases away from coastal areas. In the case of maximum temperature depressions, there is also a consistent increase toward the southern portion of the region. For minimum temperature depressions, no large-scale geographic control, except for coastal proximity, dominates the spatial distribution of the depression magnitudes. Potential geographic ''forcing'' mechanisms are evaluated. The results indicate that large sensible and, in some cases, latent heat fluxes from the lower atmosphere to the snowpack account for much of the observed temperature depressions.