This series of Haby Hints investigates problems that cause a forecast to bust. A bust occurs when a certain weather parameter is expected but one or more factors cause the forecast to be wrong. This particular Haby Hint will focus on how snow cover causes forecast problems.
Surface snow cover will result in cooler temperatures for several reasons. First, snow is a good reflector of solar radiation. Second, evaporation and sublimation from the snow are cooling processes. Third, snow is efficient at emitting longwave radiation and insolating heat under the snow surface.
An unforeseen surface snow cover will significant impact the forecasted temperatures. Expect temperatures to be cooler than forecasted if there is a surface snow cover the forecast models are not taking into account. This can be current as well as future snow cover that will occur that the models are not predicting.
The impact on temperatures is most noticeable when the skies are clear. The high and low temperatures will both end up being much cooler than expected when the forecast models are not taking into account a surface snow cover and the skies are clear / mostly clear.