Temperature °C

Precipitation

By the Sea

Atlantic and Fundy waters are relatively cold (8-12C), and they help to keep the air temperature over southwestern Nova Scotia on the cool side in spring and summer. In January, when their temperature is between 0 and 4C, these same waters moderate the harshness of winter. Farther offshore to the east, southeast, and south are comparatively warm 16C waters of the Gulf Stream. Its warmth, especially from August through October, is credited with prolonging fall - the season many Nova Scotians consider to be the best of the year.

Nova Scotia's north coast is exposed to Gulf waters which, in late August, have a maximum surface temperature of 18C. The contrast between air and water temperatures is enough to create onshore sea breezes and to hold back the onset of fall for a few weeks. In January, however, Gulf of St. Lawrence and Northumberland Strait waters become ice-covered, effectively cutting off any marine influence for the next three months.

The influence of the sea is felt in other ways. Ice conditions in the Gulf and, on occasion, in the Bay of Fundy retard the arrival of spring. Cool summer seas also help stabilize overriding air masses, thus suppressing local storm development. In addition, the merging of contrasting ocean currents - warm Gulf Stream and the cold Labrador Current - produces a great deal of sea fog that often moves far inland.

The effects of latitude and relief on climate are not as important in Nova Scotia as elsewhere. The highest mountains are the Cape Breton Highlands, part of the Appalachian mountain chain, but nowhere are they higher than 530m. Although this is not high enough to block the movement of air masses, it is sufficient to divert them and cause them to move in a direction parallel to the mountains. Locally, the Highlands help to wring additional moisture from passing weather systems and to cool temperatures by 1 or 2C.

Warmest in the East

The southwest coast around Cape Sable is frost free for over half the year, longer than any other place in Atlantic Canada and comparable to localities along the shores of Lake Erie. Most agricultural areas experience a period without frost for 120 to 130 days between late May and early October, which is the effective growing season for most crops. The Annapolis Valley has up to 140 frost-free days, but the higher highlands on Cape Breton Island have less than 100 days.

Winter temperatures are moderate along the coast. Yarmouth's average January temperature of -2.7C is the highest of any mainland station in the Maritimes. Inland, January means are between -4 and -6C. The most significant aspect of winter is the marked day-to-day variation caused by the alternation of Arctic and maritime air.

Summers are relatively cool in Nova Scotia. Afternoon summer temperatures reach 25C in the interior, but along the coast are frequently 4 to 6C cooler. At night the ocean remains a cooling source, keeping minimum temperatures along the coast about 2 to 3C below those inland. Halifax's July mean of 1 7.4C and Yarmouth's 16.3C compare closely with Vancouver's 17.3C but are somewhat cooler than Toronto's 20.6C.

Mainly Moist

Nova Scotia is wettest over the highlands of Cape Breton Island, where over 1600 mm of precipitation fall in an average year. The southern coast experiences almost as much, with totals of 1500 mm. By contrast, the north shore along the Northumberland Strait has less than 1000 mm a year.

Precipitation is slightly greater in the late fall and early winter because of the more frequent and intense storm activity. In most years there is a good supply of rain during the growing period. However, drought is not unknown in Nova Scotia. A prolonged warm, dry, and sunny spring in 1986 contributed to the worst forest fire outbreak in the province's history. The previous summer, several months of below normal precipitation dried up wells and streams, and water levels did not begin to recover until Hurricane Gloria brought heavy rains in late September.

On average, only about 15% of Nova Scotia's total annual precipitation originates as snow. An exception is northern Cape Breton Island, where the snow fraction is closer to 30%. Snowfall is relatively light near the warm Atlantic shore and near the entrance to the Bay of Fundy, where less than 150 cm may fall in one winter. Here, copious rain and freezing rain make up for the scanty snowfalls. Inland, the yearly snowfall increases to 250 cm. As a rule, elevated areas receive the greatest snowfall and have the longest snowcover season. Both the Cobequid Mountains and the Cape Breton Highlands receive in excess of 300 cm in an average snow year. These elevated areas also experience "sea-effect" snowfalls in the wake of winter storms. Heavy local snowfalls are also produced by winds blowing off the open waters of the Gulf of St. Lawrence and the Bay of Fundy.

The snowcover season, that is, the period when there is at least 2.5 cm of snow on the ground, varies considerably. Usually its duration extends from about 110 days a year along the southern coast to 140 days inland and in areas adjacent to the frozen seas. In coastal areas the snowcover may come and go. At Halifax, for instance, there is only a 50% chance that there will be snow on the ground for Christmas.

Some of the more notable provincial snowfall extremes are--greatest snowfall in one season: 653 cm at Cheticamp in 1964-65; greatest in one month: 224 cm, also at Cheticamp, March 1961; and greatest in one day: 69 cm at Yarmouth on March 19, 1885.

Misty Sunshine

Halifax's reputation as a foggy and misty city is well deserved. Each year there is an average of 122 days with fog at the International Airport and 101 days at Shearwater, on the Dartmouth side of the harbour, although on most days fog persists for less than 12 hours. The period from mid-spring to early summer is the foggiest time. Bands of thick, cool fog lie off the coast, produced where the chilled air above the Labrador Current mixes with warm, moisture-laden air moving onshore from the Gulf Stream. With onshore winds these banks of fog move far inland. Sea fog often affects the headlands by day, moving inland and up the bays and inlets at night. At other times of the year fog is much more transient and local in nature.

Besides Halifax, other foggy places are Yarmouth (118 days), Canso (115 days) and Sydney (80 days). No part of Nova Scotia is fog-free, although some places inland from the Minas Basin have no greater fog frequency than Toronto. Nova Scotia's most persistent spell of fog occurred during Canada's centennial in 1967 at Yarmouth, when over the 92 days of summer, 85 had an occurrence of 1 or more hours with fog.

Because of the extensive fogs, as well as mists, low cloud, and smog, sunshine amounts throughout the province are usually less than half the total possible. Apart from foggy Sable Island, sunshine totals range from 1700 to 1969 hours a year. July is the sunniest month inland, and August is the sunniest along the coast. Sunless days (days with less than 5 minutes of bright sunshine) amount to between 75 and 90 a year, with a marked seasonal high from November to February. Sunny days, on which less than 70% of the sky is covered with cloud in the early afternoon, amount to between 130 to 160, with a peak from July through October.

A Meteorological Moment

Remembered in weather chronicles as the Great Nova Scotia Cyclone, a calamitous hurricane swept over Cape Breton Island on August 25, 1873. The storm was unusual at that time in having traveled so far to the east after leaving the tropics. Its destructive power was also extraordinary. Ravages of the storm included 1200 vessels, 500 lives, 900 buildings, and an untold number of bridges, wharves, and dykes. Property losses were conservatively estimated at $3.5 million, an amount equivalent to $70 million in 1990 . At the height of the storm, gale-force winds were reported at Halifax, Sydney, and Truro. Also noted in the weather records for these stations were observations of an intense thunderstorm and heavy rainfalls of 50 mm or more. The Sydney weather observer remarked that this was the worst gale since 1810.

Losses were high partly because the interruption of telegraph service between Toronto and Halifax prevented storm warnings from getting through. Of significance to Canadian meteorology, this storm, perhaps more than any other event, convinced officials of the need for an improved Canadian storm warning system.

Stormy and Changeable

Storms frequently pass close to the Atlantic coast of Nova Scotia and cross the southern part of Newfoundland, producing highly changeable and generally stormy weather. Without doubt this region has more storms over the year than any other region of Canada. Winter storms are especially devastating with occasional loss of life and extensive damage to property. Packing a variety of weather conditions from hurricane-force winds to heavy precipitation, they can pass rapidly through or stall and batter the region for days. On occasion, the winds associated with these nor'easters, as they are called, exceed 150 km/h, and peak wave heights can be as high as 14 m. At high tide, these winds can cause storm surges of more than a metre. Other conditions associated with these storms include freezing spray, reduced visibility in snow, rain, or fog, and numbing wind chills, especially in the storm's wake.

In late summer and fall the remnants of a hurricane or tropical storm are felt at least once a year in Nova Scotia. The most memorable of these dying storms was Hurricane Beth on August 15-16, 1971. At Halifax, Beth brought 296 mm of rain, more than the deluge from Hurricane Hazel over Toronto and enough to wash away several bridges, damage buildings, and flood farmland.

Other severe weather phenomena include ice storms and blizzards. Each year one or two 25-cm snowfalls occur in Nova Scotia and newspaper headlines across Canada announce another paralyzing Atlantic snowstorm. When combined with strong winds, they cause enormous inconvenience and, at times, property damage and loss of life. A record snowstorm struck Halifax on February 2 - 3, 1960, producing a total of over 75 cm of snow in the downtown area and over 96 cm in the suburbs, most of it within 24 hours.

On the other hand, Nova Scotia is not known for spectacular displays of thunder and lightning. Thunderstorms occur on about 10 days of the year, about half the number that occurs in northern and central New Brunswick. Tornadoes have been recorded but are rare. One such tornado, accompanied by heavy hail and lightning, struck White Point Beach near Liverpool on January 30, 1954, but most weather watchers consider it a freakish event. Reports of waterspouts over near shore waters are received yearly.

Winds

Winds blow predominantly from the south or southwest in the summer with an average speed of about 10 to 15 km/h. In the coldest months the predominant direction is from the west and northwest with an average speed of 22 km/h.

The wind at any given location is often quite different from the wind conditions which prevail even a short distance away. The variation that occurs in both wind direction and speed results from the characteristics of natural and man-made obstructions, topography, and surface cover. Along the coast, an onshore sea breeze circulation often sets up, particularly during a warm, sunny afternoon in the spring or early summer.

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