Climate

Like location, climate has been a decisive factor in shaping the Newfoundland and Labrador experience. The overall climate of the province is marked by considerable seasonality and volatility, often with short-term changes to the weather patterns that can be difficult to predict.

Three principal factors shape the region's climate:

1. The province is in a geographic zone characterised by marked seasonal differences in the amount of energy received from the sun, and by winds blowing predominantly from the west;
2. The position of Newfoundland with respect to the Canadian mainland, and the division of the province into island and mainland portions, leads to distinctive onshore and offshore local airflow features for the island and Labrador;
3. The extensive area of cold water and seasonal ice offshore, including the Labrador Current system, has a direct bearing upon climate and weather; and the distinctly warmer Gulf Steam/North Atlantic Drift system to the southeast of the Grand Banks affects the properties of air reaching the province from the south and east.

In addition, landform features such as prominent uplands, and mountain ranges, and sheltered valleys and lowlands, influence the finer details of climate and weather.

Because the province extends across a considerable span of latitude (46.5-60.5°N) and longitude (from the continental interior of western Labrador to the southeastern peninsulas of the island with their exposure to the sea), the timing, duration and climatic character of the seasons varies substantially across the province.

Winter, defined here as the season having long-term ("climatological") average daily temperatures below freezing (0°C), varies in length from approximately six months over northern and western Labrador (November through April) to four months (December through March) over much of the island. Over much of the interior of Labrador temperatures remain in the range -5 to -30°C for prolonged periods, with a continuous snow cover, but due to more frequent polar and arctic high pressure patterns, the weather is clear and drier.

The southeast corner of Labrador has winter weather more akin to the island, being subject to vigorous storm systems approaching from the south and southwest, resulting in more frequent precipitation and high winds. On the island especially, a major characteristic of winter is the wide variation in snowfall, and the depth and duration of snow cover, both spatially and between winters, which is of particular significance for water resources, ground transportation systems and winter recreational activity.

The onset of spring is delayed by a prevalence of cool polar air masses and low sea surface temperature. Mean daily temperatures reach the melting point earliest over the Avalon and Burin peninsulas (near April 1), but about a month later over lowland southeastern areas of Labrador and the Goose Bay area, and not until the second half of May over northern Labrador. Coastal areas exposed to the north and east endure repeated spells of low cloud, fog and light precipitation, though areas well inland and to the west are much less affected. In general, however, there is a significant reduction in both precipitation and the frequency of high winds during the period from May until July, more especially on the island.

The retreat of the polar front jet stream to the north, combined with the shift in prevailing wind direction to southwest, causes a change in the temperature patterns by mid-late June. The highest daily maximum temperatures of summer (typically 27-31°C) normally occur well away from the south coast, which is now more vulnerable to sea fog. There is a marked cooling northward on the Northern Peninsula, whilst Labrador, which remains closer to the northern summer cyclone tracks, normally experiences a wetter summer than the island.

During the fall the southern coasts of the island cool relatively slowly, owing to the thermal lag of the ocean and delayed onset of colder air masses from the north. Consequently, the mean daily air temperature on the Avalon Peninsula does not fall below 0°C until almost mid December, two months later than for western and northern Labrador. Over the entire province there is a marked increase in precipitation and strong wind frequencies during October and November.

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