Snow covered the northeastern United States on last day of meteorological winter, 2014. Climatologists and meteorologists break seasons down into three-month groups, based on annual temperature and our calendar. This method is helpful for weather observing and forecasting, and for planning consistent agricultural dates, such as expected first frosts or best planting date. Meteorological winter – the season where temperatures are, on average, coldest and when snow is most likely to fall – runs from December 1 to February 28 in the United States and Canada.
Winter can also be defined by the astronomical calendar, which is based on the rotation of the Earth around the sun. In this method, the seasons are defined by two solstices (times when the sun’s path is furthest from the Earth’s equator) and two equinoxes (the times when the sun passes directly above the equator). In the Northern Hemisphere, winter begins on the winter solstice, which falls on or around December 22 and ends on or around March 21, at the vernal (spring) equinox.
On February 28, 2014, the Moderate Resolution Imaging Spectroradiometer aboard NASA’s Aqua satellite captured this true-color image of a sunny winter day in the northeastern United States. Snow stretches from Maine west to Indiana and south along the ridges of the Appalachian Mountains well into West Virginia. In Canada, the landscape appears greener, primarily because snow lies on conifers (evergreen) trees in the boreal forest regions. The Great Lakes, with the exception of Lake Ontario, are almost completely covered with ice.