More than any other season of the year, winter exhibits much variability in climate and weather across Newfoundland and Labrador. The elements associated with this season - below freezing air temperatures, snowfall and other forms of freezing precipitation, the depth of snow on the ground and high wind speeds - all show considerable spatial variation in their frequency of occurrence across the province.
The steady northwestward decrease in average air temperature during the winter period is due not only to increasing latitude (and therefore less solar energy received at this time of year), but also to an increased frequency of colder Arctic air masses.
As winter advances, sea ice formation and movement off the coasts of Labrador and northern parts of the island also help to lower temperatures. Around the Avalon Peninsula and off much of the south coast the ice concentration is usually lighter or non-existent, allowing temperatures to be moderated by the open water (see climagraphs: St. John's, St. Lawrence, with legend.
Lowest temperatures occur over snow or ice-covered surfaces on clear nights during Arctic air outbreaks, when night minima of -10 to -25°C are widespread over the island, dipping to -30 to -35°C in low-lying central interior valleys, and over much of Labrador away from the coastal fringe. The absolute minimum recorded temperatures are -41°C on the island (Badger) and -54°C in Labrador, at Wabush/Labrador City, where ice fogs quite regularly form, produced by a combination of calm air, frigid temperatures and vapour emissions from the iron ore processing plants.
Interludes of mild, above freezing conditions are experienced with increasing frequency towards the south and east, in most years, with temperatures typically climbing to 5-10°C, though often accompanied by strong winds and rain. Such winter thaws are much less frequent and weaker over Labrador.
Although winter air temperatures in themselves are not often as severe on the island as on the mainland, their chilling effect is significantly increased by strong winds, which are regularly experienced over most of the island and southeastern Labrador. During strong Arctic air outbreaks the "windchill equivalent temperature" is typically in the -25 to -35°C range on the island, lowering to the -40s over Labrador.
Surface wind speeds at average 20-30 km/hour around the coasts, with 50-80 km/hr typically sustained during low pressure systems (see climagraphs: St. John's, St. Lawrence, Port aux Basques, Battle Harbour, with legend. Very strong gusts (120-140 km/hr) are a feature along the south and west coasts of the island, whenever strong offshore winds descend from the hills immediately inland, especially where narrow valleys exit towards the sea (for example the Wreckhouse area, near Port aux Basques, and Western Brook Pond outlet at Gros Morne National Park).
However, wind speeds are considerably reduced, with more frequent calms, for the more sheltered lowland valleys, basins and inlets on the island and in Labrador, such as Head of Bay d'Espoir, Bay of Islands and lower Humber valley, the lower Exploits valley, the Goose Bay area and Labrador City/Wabush (see climagraphs: Goose Bay, Wabush with legend. Furthermore, when light winds are accompanied by winter sunshine, the "apparent" temperature is further increased; this favorable combination is most often experienced over the central interior sections of both the island and Labrador.
Of considerable relevance for the overall human perception and experience of winter climate are the frequency, amount and types of precipitation. Again there are strong contrasts around the province.
Precipitation amount and frequency are generally at a maximum for locations on the coast or at higher elevations immediately inland, where between half and three quarters of winter days include some form of precipitation (see climagraphs: St. John's, St. Lawrence, Port aux Basques, Corner Brook, Gander with legend. There is a trend to reduced precipitation over the Northern Peninsula and to the north and west in Labrador (see climagraphs: St. Anthony, Goose Bay, Wabush, Nain with legend. Alternation between frozen and liquid forms becomes increasingly frequent toward the south and east on the island, associated with the varying air mass types and the exposure to open salt water influence. Winter storms tracking through these areas quite often deliver a sequence beginning with snow, followed by ice pellets and/or freezing rain or rain, then reverting to snow flurries, creating variable surface conditions.
The proportion of the total winter precipitation falling as snow, being linked to average temperature, increases toward the west and north (see climagraphs: Corner Brook, Gander, St. Anthony, Battle Harbour, Goose Bay, Wabush, Nain with legend. During the majority of winters snowfall amount and frequency are greatest for (1) the western section of the island between Stephenville and Daniel's Harbour and (2) certain coastal areas exposed to the east, northeast and north between Cartwright, Labrador and the Gander area.
Both the depth and duration of snow cover on the ground are also at a maximum for these areas, and increase significantly with altitude, such that over the highest elevations (700-800 m) of the Long Range Mountains on the island a complete snow cover typically prevails from mid-late November until early May, with late-lying snow patches persisting until August. The Mealy Mountains of eastern Labrador (elevations reaching 1200 m) also harbour considerable snow cover, from October until early June.