Abstract
The sensitivity of temperature forecast biases to the presence or absence of snow cover is investigated for the December–March periods of 1985–1986 and 1986–87 at ten stations in the northeastern United States. Forecast biases are consistently “warmer” for snow-covered (defined here as ≥2″) versus open conditions in situations where the MOS forecast equations do not include snow cover as an explicit predictor. The differences are most often statistically significant for the forecasts of minimum temperature. However, this aspect of forecast performance is superimposed on a general cold bias for both maximum and minimum temperature forecasts, and the two effects tend to cancel for snow-covered conditions. No significant differences in forecast bias between snow-covered and open conditions are found for the few cases where snow cover is included explicitly as a predictor in the MOS forecast equations.
