The climate of Moscow is dominated by westerly winds from the Atlantic. Precipitation is moderate, about 23 inches (580 mm) a year. Snow is common, beginning usually about mid-November and lasting generally until mid-March; the city is well-equipped to keep the streets clear. Winters are long, yet they are significantly milder than in similar climatic regions of North America. Southerly airstreams occasionally bring days with temperatures above freezing. On the other hand, northerly winds from the Arctic bring very sharp drops in temperature, often accompanied by clear, brisk weather with low relative humidity. Thus, although the January average temperature is 14 °F (−10 °C), there can be a lot of variation; temperatures have dropped to near −45 °F (−43 °C). Spring is relatively brief, and the temperature rises rapidly during late April. Summers are warm, and July, the warmest month, has an average temperature in the mid-60s F (about 18 °C); temperatures nearing 100 °F (38 °C) have been reached in August. Rainy days are not uncommon, but the summer rainfall often comes in brief, heavy downpours and thunderstorms. Autumn, like spring, is short, with rapidly falling temperatures.
Until the late 1950s there was increasing air pollution in Moscow. Smog was common, often with heavy concentrations of sulfur dioxide. A major campaign to control noxious (unhealthy) emissions was launched, assisted greatly by changing from coal to natural gas as the principal fuel. Some factories that had contributed to pollution were moved out of the city. Slight improvement in Moscow’s air had been marked, but since the 1980s the growing number of motor vehicles and the increase in the number of power generators have once again increased the concentrations of such exhaust pollutants as carbon monoxide and sulfur dioxide in Moscow.
Though Beijing is not far from the sea, the wind comes mainly from the northwest throughout the year, so effects of the ocean on the region’s weather are minimal. Local geography also has a great effect on Beijing’s climate. Because it lies in a lowland area and is protected by mountains, the city is a little warmer in winter than other areas of China located at the same latitude; nonetheless, the mean monthly temperature drops below 50 °F (10 °C) for five months out of the year. In addition, wind direction in Beijing is influenced by geography, with changes occurring from day to night. Generally, there are more southerly winds in the day but northerly or northwesterly winds at night.
The annual mean temperature of the city is 53 °F (12 °C). The coldest month is January, when the monthly mean is 24 °F (–4 °C), and the warmest month is July, when it is 79 °F (26 °C). In an average year, the city experiences 132 days of freezing temperatures between October and March; the mean annual precipitation is 25 inches (635 mm), with most of the total falling from June to August. July is ordinarily the wettest month of the year, with an average of 9 inches (230 mm).
The region’s precipitation is quite variable. In 1959—an extremely wet year for Beijing—the total precipitation amounted to 55 inches (1,400 mm), whereas in 1891—an extremely dry year—only 7 inches (180 mm) fell. The average number of rainy days per year is about 80, and the average relative humidity for the city is 57 percent.
Winter in Beijing is long and usually begins in late October, when northwesterly winds gradually gain strength. This seasonal wind system dominates the region until March; the Siberian air that passes southward over the Mongolian Plateau and into China proper is cold and dry, bringing little snow or other precipitation. The monthly mean temperature from December to February is below freezing. Spring, the windiest season, is short and rapidly becomes warm. The high spring winds produce an evaporation rate that averages about nine times the total precipitation for the period and can cause droughts that are harmful to agriculture. Dust storms in the region, made worse by increasing desertification in Inner Mongolia, are common in April and May. In addition to being the season of torrential rains, summer is rather hot, as warm and humid air from the southeast often penetrates into North China. Autumn begins in late September and is a pleasant, though short, season with clear skies and comfortable temperatures.
The temperate climate of the city is characteristic of the Río de la Plata’s coastal plain. The city is hot and humid during the summer months of December to March, with temperatures in the low to mid-80s (about 28 °C). The autumn and spring are characterized by fluctuating temperatures and quickly changing weather. The winter months of June to September are mild but humid, with mean temperatures in the low 50s F (about 11 °C). The average annual temperature is about 60 °F (16 °C). Frosts occur from May to September, but snowfall is extremely rare. Winds are generally of low speed and are more frequent during the season of electrical storms, between September and March. Rainfall is heaviest in March. Average annual rainfall is about 45 inches (1,140 mm).
Climatically, Florida is divided into two regions. The tropical zone lies generally south of a west-east line drawn from Bradenton along the south shore of Lake Okeechobee to Vero Beach (includes Miami), while north of this line the state is subtropical. Summers are uniform throughout Florida. Freezing weather of short duration (but often crippling to agriculture) can occur as far south as Miami, but the Keys have never had frost.
Rainfall is heaviest in summer, with drier weather in the winter months. The average annual rainfall ranges from 40 inches (1,000 mm) in Key West to 62 inches (1,575 mm) in West Palm Beach. Snow falls occasionally in the northern areas and has been reported as far south as Miami. The west coast of the state is particularly prone to lightning strikes in the summer months. Hurricanes (tropical cyclones) strike the state about once a year on the average, although Florida is no more vulnerable to these storms than are the other Gulf Coast states or, indeed, the entire Atlantic coast as far north as Boston. The hurricane season is from June to November, though September is the month during which they are most likely to occur. Among the more notable storms are the Great Hurricane (1928), which killed thousands of Floridians and has remained the most deadly to hit the state; and Hurricane Andrew (1992), which devastated southern Florida and caused extensive property damage.
Average annual temperatures show little variation, ranging from 68 °F (20 °C) in Tallahassee in the north to 77 °F (25 °C) at Key West in the south. Corresponding monthly averages range from the mid-40s °F (6 to 8 °C) in the north to the mid-50s °F (12 to 14 °C) in the south in January, and are in the lower 80s °F (27 to 29 °C) in August.
California’s climate is marked by two seasons—a wet and a dry. Except on the coast, the dryness of the air and the resulting rapidity of evaporation reduce the severity of summer heat. Precipitation ranges from more than 170 inches (4,300 mm) in the northwest to traces in the southeastern desert, but moderate temperatures and rainfall prevail along the coast. The climate also changes rapidly with elevational extremes. DeathValley, with its lowest point at 282 feet (86 metres) below sea level, is the hottest and driest place in North America. Its temperatures easily soar into the 100s F (about 48 °C) in the summer, and average annual rainfall is only about 2 inches (50 mm). Summer temperatures in the low-lying Colorado Desert can reach as high as about 130 °F (54 °C), and annual precipitation there averages only 3 to 4 inches (75 to 100 mm). In the higher eastern deserts of California, summer temperatures are more moderate. Winter temperatures in the Sierra Nevada can drop to near freezing. The average annual temperature is in the mid-60s F (about 18 °C) in Los Angeles, with an annual precipitation average of about 14 inches (350 mm). In San Francisco temperatures average in the mid-50s F (about 14 °C), with annual precipitation of about 20 inches (508 mm). On the coast, temperatures seldom exceed 90 °F (32 °C) or drop to freezing, and humidity is low.
Hawaii lies just below the Tropic of Cancer, and its mild tropical climate is considered by many people to be the world’s ideal. Although the weather is often humid by U.S. mainland standards, temperatures are conditioned by the northeast trade winds, which prevail most of the year and make living on the islands delightfully comfortable. As moisture-laden air is carried over the islands, most frequently by the trade winds, it is likely to condense, form cap clouds, and dissipate against the shores and mountains of the windward coasts, which are therefore more lush in foliage (plants) than the leeward coasts.
Most Hawaiians recognize only two seasons: summer and winter. Summer (kau) lasts from May through October, with high temperatures and reliable trade winds. The rainy season, winter (hoʿoilo), lasts from November to April, with cooler temperatures and frequent rainstorms.
The average temperature in Honolulu is in the low 70s F (about 22 °C) in the coolest month and in the high 70s F (about 26 °C) in the warmest, though extreme temperatures in the high 50s F (about 14 °C) and low 90s F (about 33 °C) have been recorded there.
Rainfall variations throughout the state are dramatic. Mount Waialeale, on the island of Kauai, is often called the wettest spot on Earth, with an annual average rainfall of about 450 inches (11,430 mm). The driest area of the state is at Kawaihae, on the island of Hawaii, where the average annual rainfall is only about 9 inches (220 mm). The average yearly rainfall in Honolulu is 23 inches (590 mm), and in Hilo (on the Big Island), one of the state’s wettest cities, it is about 130 inches (3,300 mm).
Glaciers cover the slopes of Everest to its base. Individual glaciers on the sides of the mountain are the Kangshung Glacier to the east; the East, Central, and West Rongbuk (Rongpu) glaciers to the north and northwest; the Pumori Glacier to the northwest; and the Khumbu Glacier to the west and south, which is fed by the glacier bed of the Western Cwm, an enclosed valley of ice between Everest and the Lhotse-Nuptse Ridge to the south. Glacial action has been the primary force behind the heavy and continuous erosion of Everest and the other high Himalayan peaks.
The mountain’s drainage pattern radiates to the southwest, north, and east. The Khumbu Glacier melts into the Lobujya (Lobuche) River of Nepal, which flows southward as the Imja River to its confluence with the Dudh Kosi River. In Tibet the Rong River originates from the Pumori and Rongbuk glaciers and the Kama River from the Kangshung Glacier: both flow into the Arun River, which cuts through the Himalayas into Nepal. The Rong, Dudh Kosi, and Kama river valleys form, respectively, the northern, southern, and eastern access routes to the summit.
The climate of Everest is always hostile to living things. The warmest average daytime temperature (in July) is only about −2 °F (−19 °C) on the summit; in January, the coldest month, summit temperatures average −33 °F (−36 °C) and can drop as low as −76 °F (−60 °C). Storms can come up suddenly, and temperatures can plummet unexpectedly. The peak of Everest is so high that it reaches the lower limit of the jet stream, and it can be buffeted by sustained winds of more than 100 miles (160 km) per hour. Precipitation falls as snow during the summer monsoon (late May to mid-September). The risk of frostbite to climbers on Everest is extremely high.
Although Tokyo lies somewhat farther south than Washington, D.C., the two cities have similar climates. In both the one really uncomfortable season is the summer, when humidity is extreme, and the temperature may rise to above 100° F (38° C). On most August days in Tokyo it rises to near 90° F (32° C), and it is not the heat but the humidity that matters. The winters are brisk but not savagely cold. Heavy snowstorms usually come in early spring and quickly melt away. The temperature sometimes drops below freezing but only slightly. Winter is the sunniest season of the year and has the cleanest air. It is the only season when one would not be startled to see Mount Fuji from a high building near the centre of the city.
Spring and autumn are delightful, though the weather tends to be more turbulent (stormy and windy) than in Washington. There are rainy periods in early summer and early autumn. The autumn can have typhoons, the Pacific equivalent of the hurricane. It is a rare year in which one or more does not strike the region. The flowers of spring and the leaves of autumn have been endlessly and justly celebrated in Japanese poetry. May, with its peonies, azaleas, wisteria, and dogwood, is the most flowery month, although the more famous cherry blossoms come early in April. Plums, camellias, and witch hazel bloom yet earlier. At no time of the year, even the “dead” of winter, is the city without outdoor blossoms.
The Bahamian climate, mild throughout the year, is one of the great attractions of the area. The average temperature varies from the low 70s F (about 21 °C) during the winter to the low 80s F (about 27 °C) during the summer, and extremes seldom fall below the low 60s F (about 16 °C) or rise above the low 90s F (about 32 °C). The average annual rainfall is about 44 inches (1,120 mm), occurring mostly during the summer months. Prevailing winds, coming from the northeast in winter and from the southeast in summer, lend a cooling influence to a generally humid atmosphere. Tropical cyclones (hurricanes) pose a threat during the period from June to November and have occasionally caused great destruction.
The country’s tropical climate is characterized by heavy precipitation and high temperatures and humidity. The Equator crosses the country just north of Liranga. In the north a dry season extends from November through March and a rainy season from April through October, whereas in the south the reverse is true. On both sides of the Equator, however, local climates exist with two dry and two wet seasons.
Annual precipitation is abundant throughout the country, but seasonal and regional variations are important. Precipitation averages more than 48 inches (1,200 mm) annually but often surpasses 80 inches (2,000 mm).
Temperatures are relatively stable, with little variation between seasons. More variation occurs between day and night, when the difference between the highs and lows averages about 27 °F (15 °C). Over most of the country, annual average temperatures range between the high 60s and low 80s F (low and high 20s C), although in the south the cooling effect of the Benguela Current may produce temperatures as low as the mid-50s F (low 10s C). The average daily humidity is about 80 percent.
The climate of El Salvador is tropical but is moderated by elevation in the interior; in general it is warm rather than hot, varying between the high 50s and low 70s F (about 15 and 23 °C). Heavy rains, known as the temporales, fall in the winter season, from May to October. The dry summer season lasts from November to April. There is considerable climatic variation in the different regions. The Pacific lowlands and low areas in the middle Lempa River valley have mean monthly temperatures between the high 70s and mid-80s F (about 25 and 29 °C). In San Salvador, the capital, which is 2,238 feet (682 metres) above sea level, the maximum monthly mean temperature is in the mid-90s F (about 34 °C), in March, and the lowest monthly mean is in the low 60s F (about 17 °C), in January. In the mountains, above 4,800 feet (1,460 metres), mean monthly temperatures vary between the low 60s and low 70s F (about 17 and 22 °C).
Annual precipitation on the Pacific lowlands averages about 65 to 70 inches (about 1,700 mm); on the southern and northern mountain ranges, at elevations between 2,000 and 3,500 feet (600 and 1,060 metres), the average is between 70 and 100 inches (1,800 and 2,500 mm); the higher mountains receive a little more. Annual precipitation recorded in the deeper valleys and surrounding plateaulike areas is between about 45 and 60 inches (1,100 and 1,500 mm).
The unique weather and climate of Antarctica provide the basis for its familiar appellations—Home of the Blizzard and White Desert. By far the coldest continent, Antarctica has winter temperatures that range from −128.6° F (−89.2° C), the world’s lowest recorded temperature, measured at Vostok Station (Russia) on July 21, 1983, on the high inland ice sheet to −76° F (−60° C) near sea level. Temperatures vary greatly from place to place, but direct measurements in most places are generally available only for summertime. Only at fixed stations operated since the IGY have year-round measurements been made. Winter temperatures rarely reach as high as 52° F (11° C) on the northern Antarctic Peninsula, which, because of its maritime influences, is the warmest part of the continent. Mean temperatures of the coldest months are −4° to −22° F (−20° to −30° C) on the coast and −40° to −94° F (−40° to −70° C) in the interior, the coldest period on the polar plateau being usually in late August just before the return of the sun. Whereas midsummer temperatures may reach as high as 59° F (15° C) on the Antarctic Peninsula, those elsewhere are usually much lower, ranging from a mean of about 32° F (0° C) on the coast to between −4° and −31° F (−20° and −35° C) in the interior. These temperatures are far lower than those of the Arctic, where monthly means range only from about 32° F in summer to −31° F in winter.
Wind chill—the cooling power of wind on exposed surfaces—is the major debilitating weather factor of Antarctic expeditions. Fierce winds characterize most coastal regions, particularly of East Antarctica, where cold, dense air flows down the steep slopes off interior highlands. Known as katabatic winds, they are a surface flow that may be smooth when moving slowly but that may also become greatly turbulent, sweeping high any loose snow, if the winds become faster. This turbulent air may appear suddenly and is responsible for the brief and localized Antarctic “blizzards” during which no snow actually falls and skies above are clear. During one winter at Mirnyy Station, gusts reached more than 110 miles per hour on seven occasions. At Commonwealth Bay on the Adélie Coast the wind speed averaged 45 miles per hour (20 metres per second). Gusts estimated at between 140 and 155 miles per hour on Dec. 9, 1960, destroyed a Beaver aircraft at Mawson Station on the Mac. Robertson Land coast. Winds on the polar plateau are usually light, with monthly mean velocities at the South Pole ranging from about 9 miles per hour (4 metres per second) in December (summer) to 17 miles per hour (8 metres per second) in June and July (winter).
England's climate is dominated by the influence of the sea. Winters are mild, summers cool, and rain falls in all seasons. Winter temperatures are modified by the influence of the warm North Atlantic Current, which moves along the west coast of the British Isles. Summer temperatures are influenced by England's location in northern latitudes. Most of England has summer temperatures of 60 to 62° F (16 to 17° C) and winter temperatures of 40 to 42° F (4 to 6° C), with somewhat warmer temperatures in the southwest. The amount of rain and snow varies greatly with location. It is about 20 inches (50 centimeters) on the average per year in parts of the east and more than 45 inches (115 centimeters) in the southwest. The mountains of the Lake District receive the most precipitation, with more than 80 inches (200 centimeters) on the average in a year. Because of the mild winter temperatures, snow does not lie for long even on the mountains.
Modern London has the equable climate of South East England, with mild winters and temperate summers. The average daytime air temperature is 52 °F (11 °C), with 42 °F (5.5 °C) in January and 65 °F (18 °C) in July. Statistics show that the sun shines, however briefly, on five days out of six. Londoners shed their winter overcoats in April or May and begin to dress warmly again in late October. The prevailing wind is west-southwest. Because of the sheltering effect of the Chiltern Hills and North Downs, the city has slightly less rainfall than the Home Counties. In an average year one can expect 200 dry days out of 365 and a precipitation total of about 23 inches (585 mm) evenly distributed across the 12 months.
The amount of sleet and snow is less predictable. It varies greatly from year to year around a long-run statistical average of 20 days. The snowiest winter on record was 1695, with snow falling on 70 days. When snow does fall (generally only in the first three months of the year), it rarely accumulates. Semi-hardy plants can winter over in London gardens, though only in the most sheltered and sunny spot will a London vine bear grapes sweet enough for wine making.
NOTE: Greenwich is in the south of England, near London.
The tropical climates lie in the low latitudes and are dominated by tropical and equatorial air masses. They are warm all year with at most a minor cool season. In areas with rainy tropical, or tropical rainforest climates, precipitation is heavy, usually averaging more than 80 inches (200 centimeters) per year. Humidity is high. Thunderstorms occur almost every day. Every month has a mean temperature close to 80° F (27° C). Temperature variations are small, so that many such locations never experience high temperatures over 100° F (38° C) or lows below 60° F (16° C). Vegetation consists of dense rainforests of broad-leaved evergreen trees. Poorly drained areas have mangrove swamps. Where tree cover is thin and sunlight reaches the ground, there is dense undergrowth known as jungle.
Rainy tropical climates generally occur located in the equatorial lowlands and along mountainous tropical coasts exposed to the moist easterly trade winds. The Amazon Basin in South America and the Congo Basin in Africa are the largest continuous areas that have a rainy tropical climate. Other areas are in the islands of Southeast Asia, the eastern coast of Madagascar, and the windward coasts of Central America.
Almost all of South Africa lies within the temperate climate zone, and extremes of heat and cold are rare. Because of the country's generally high elevation, even the tropical and near-tropical northern areas are much cooler than would be expected based on their latitude. The climate is strongly influenced by the oceans that surround the country on three sides. Along the Atlantic coast the cold, northward-flowing Benguela Current cools the air and thus causes fog. The warm Agulhas Current sweeps southward along the east and southeast coasts, bringing higher temperatures from KwaZulu-Natal to Eastern Cape and Western Cape. Most of the country is dry, though the east receives more rainfall than the west.
The climate of Cape Town is Mediterranean in type; it is locally modified by the mass of Table Mountain and by the cold Benguela Current of the South Atlantic Ocean. The average high temperature is 70° F (21° C), in January and February, and the average low is 55° F (13° C), in July, but temperatures are cooler on the mountain slopes and on the coast. Freezing occurs infrequently. On the average, rain falls on 69 days of the year; about half of the 26 inches (660 millimeters) of annual rainfall occurs between June and August, the southern winter. The amount of rainfall varies with proximity to the mountain, with areas close to the slopes receiving as much as twice the precipitation of areas farther away. The winds, generally strong, come from the northwest in winter and vary from between southeast and southwest in summer. Southerly winds produce a cloud cover over Table Mountain known as the “tablecloth.” These winds are collectively referred to as the “Cape doctor” because they keep air pollution at a low level.
Egypt has an arid climate. Alexandria has the highest rainfall, with a mean of 7.4 inches (18.8 centimeters) annually. Other parts of the Mediterranean coast receive even less rainfall, with only 2.5 inches (6.4 centimeters) annually at Port Said. Most rain falls in the winter, none in the summer. The mean annual temperature is 69° F (20° C), reaching a high of 80° F (27° C) in the summer.
Cairo is a desert capital. It receives slightly less than 1 inch (2.5 centimeters) of rainfall annually, and the mean annual temperature is 71° F (22° C). In the spring and summer early morning fogs on the Nile Delta provide some additional moisture. The rest of Egypt has only a few centimeters of rainfall annually. Most of the year is hot and dry, and periodic droughts extending over several years are common. Aswan, for example, has a mean annual rainfall of 0.2 inch (0.5 centimeter) and a temperature of 80° F (27° C) with a high of 94° F (34° C) in the summer.
During the spring, hot, dry khamsin winds blow northward from the Sahara across Egypt to the Mediterranean coast. The khamsin, which often produces sandstorms, can last for several days, destroying crops. Egypt has no forests and only a few permanent grasslands for pasture. At best the deserts support sparse drought-resistant scrub vegetation.
Cairo has only two seasons: approximately eight months of summer and four months of winter. In the hottest of the summer months—June, July, and August—the average daily maximum temperature is 95 °F (35 °C), and the average daily minimum is 70 °F (21 °C). The summer temperature has reached as high as 117 °F (47 °C). During winter the strong Tropic of Cancer sun makes for warm, dry days, but nights are cool and humid, often freshened by breezes from the Nile. The average daily maximum temperature in January–February is 67 °F (19 °C), and the average daily minimum is 47 °F (8.5 °C).
Alberta has a continental climate, with cold winters and warm summers (more sunshine than any other Canadian province). In the winter, blizzards are common, with bitterly cold temperatures, high winds, and driving snow. The mean January temperature is 9.5° F (–12.5° C) at Edmonton. The lowest on record is –78° F (–61° C) at Fort Vermilion. The chinook—a dry, westerly wind that is warmed as it descends from the mountains—may blow all winter, bringing almost spring-like weather.
Temperatures vary less in the summer. The mean July temperature is 63.5° F (17.5° C) at Edmonton. The highest recorded was 108° F (42° C) at Medicine Hat. In the north, temperatures may be almost as high as in the south, owing to the long hours of summer sunlight and the lower altitude.
Rainfall is usually adequate for crops, except in the southeast. There the chinook prevents much snow from falling and carries off summer moisture.
Winters are dry, sunny, and cold, though in the south the chinook winds, which occur when warm, dry air of Pacific origin descends the eastern slopes of the Rockies, can raise temperatures by 40 °F (22 °C) in an hour or less. Summers are warm and wetter (except in drought years), with occasional destructive hailstorms and tornadoes. Edmonton’s mean and extreme temperatures are 6 °F and -59 °F (-14 °C and -51 °C) in January and 60 °F and 95 °F (16 °C and 35 °C) in July. Annual precipitation in Edmonton averages 18 inches (460 mm), compared with 12 inches (300 mm) in the dry southeast and more than 50 inches (1,270 mm) in the mountains. About half the precipitation falls from June to August.
Kolkata has a subtropical climate with a seasonal regime of monsoons (rain-bearing winds). It is warm year-round, with average high temperatures ranging from about 80 °F (27 °C) in December and January to nearly 100 °F (38 °C) in April and May. The average annual rainfall is about 64 inches (1,625 mm). Most of this falls from June to September, the period of the monsoon. These months are very humid and sometimes sultry. Devastating floods have inundated parts of Kolkata in some years, including 1978 and 2000. During October and November the rainfall dwindles. The winter months, from about the end of November to the end of February, are pleasant and rainless; fogs and mists occasionally reduce visibility in the early morning hours at this season, as also do thick blankets of smog in the evenings. The atmospheric pollution has greatly increased since the early 1950s. Factories, motor vehicles, and thermal-generating stations, which burn coal, are primary causes of this pollution, but monsoon winds act as cleansing agents by bringing in fresh air masses and also hastening the removal of water pollution.
Finland has a high-latitude, continental type climate. In the southern part (including Helsinki), moderating winds off the North Atlantic and the Baltic Sea prevent severe weather conditions. The northern portions of the country have long, severe winters and short, cool summers.
Frost can occur during any month in the north, and even in the south the growing season averages only three months or less. Because of the country's far northern latitude, however, it has long hours of summer daylight, which somewhat offsets the short growing season. The annual average precipitation ranges from 24 inches (61 centimeters) in the south (where Helsinki is) to 16 inches (41 centimeters) in the far north. Winter snowfall is considerable.
The part of Finland north of the Arctic Circle suffers extremely severe and prolonged winters. Temperatures can fall as low as −22 °F (−30 °C). In these latitudes the snow never melts from the north-facing mountain slopes, but in the short summer (Lapland has about two months of the midnight sun), from May to July, temperatures can reach as high as 80 °F (27 °C). Farther south, near Helsinki, the temperature extremes are slightly less marked, as the Baltic Sea- and Gulf Stream-warmed airflow from the Atlantic keeps temperatures as much as 10 degrees higher than at similar latitudes in Siberia and Greenland. Winter is the longest season in Finland. North of the Arctic Circle the polar night lasts for more than 50 days; in southern Finland the shortest day lasts about six hours. Annual precipitation, about one-third of which falls as sleet or snow, is about 25 inches (600 mm) in the south and a little less in the north. All Finnish waters are subject to some surface freezing during the winter.
Most of Italy has a Mediterranean type of climate, which has cool, rainy winters and hot, dry summers. In Naples, high temperatures in July and August often exceed 90° F (32° C), while the damp, chilly winter is lessened by many brilliant, sunny days. Winter temperatures rarely fall to freezing, and the snow occasionally appearing on Mount Vesuvius is seldom seen in the town itself. Winter is the rainy season, when streambeds that remain empty during much of the year fill to overflowing and flash floods are common. Summers are dry, and certain crops, especially fruits and vegetables, must be irrigated throughout much of the peninsula and on the islands.
Farther south, where the coastal areas extend a great distance inland and are flatter, the mean temperature and annual rainfall are 61.9 °F (16.6 °C) and 31.4 inches (800 mm) at Naples. The sirocco, a hot, very humid, and oppressive wind, blows frequently from Africa and the Middle East.
Situated in north-central Chile in the fertile Central Valley, Santiago lies at an altitude of about 1,700 feet (520 meters) in a depression formed by mountain ranges. To the east are the Andes, and to the west are the coastal ranges. Most of the Andean peaks are snow-covered in winter.
The city spreads on both banks of the Mapocho River, which flows through the city in a man-made canal. Santiago is subject to frequent earthquakes, and many of its historic buildings have been damaged repeatedly. In recent history a 2010 earthquake struck about 200 miles (325 kilometers) south of the city, causing widespread damage throughout the region. The mild climate has mean summer (January) temperatures of 68° F (20° C) and winter (July) temperatures of 46° F (7.7° C). Annual precipitation of about 15 inches (38 centimeters) is concentrated in the winter months.
Central Chile occupies an area roughly between 30° and 40° S. latitude. It is located in a valley (known as the Central Valley or Vale of Chile) that is cradled between the coastal mountains and the Andes. This heavily populated area is the economic, political, and agricultural core of the nation. The valley's fertile soils produce most of the nation's food supply. The climate of central Chile is temperate, with most rainfall occurring from May to August, during the Southern Hemisphere's wintertime. Summers are warm and typically rainless. To the east of Santiago is the towering, snow-capped Mount Tupungato. Crossed by low hills, the valley continues southward before reaching the sea near Puerto Montt.
The tropical climate of Uganda is modified by elevation and, locally, by the presence of the lakes. The major air currents are northeasterly and southwesterly. Because of Uganda's equatorial location, the length of daylight is nearly always 12 hours. All of these factors, combined with a fairly constant cloud cover, ensure a consistent climate throughout the year.
Most parts of Uganda receive enough precipitation; annual amounts range from less than 20 inches (500 mm) in the northeast to a high of 80 inches (2,000 mm) in the Sese Islands of Lake Victoria. In the south, two wet seasons (April to May and October to November) are separated by dry periods, although the occasional tropical thunderstorm still occurs. In the north, a wet season occurs between April and October, followed by a dry season that lasts from November to March.
The high amount of solar radiation throughout the year means there is not much variation of temperature: the mean monthly variation is less than 9 °F (5 °C) at most stations. Ground frosts rarely occur below 8,200 feet (2,500 meters).
The most extreme winter cold and summer heat in the Arctic are not at the pole because the Arctic Ocean prevents extremes. The water absorbs heat during the summer and gives it out in the winter.
Greater extremes occur near the Arctic Circle because the land there is less effective than water in storing heat. Alaska has had a winter temperature of –80° F (– 62° C). In summer the temperature has reached 100° F (38° C). The coldest weather in the Arctic regions occurs near Verkhoyansk in Siberia. The January temperature there can reach –90° F (–68° C). The Arctic is warmer than Antarctica.
Within the Arctic Circle winter cold is bearable because there is little wind. Blizzards and gales occur only when the air is flowing strongly outward across the Arctic Circle or where a break in the land level disturbs the circulation. The winter air is dry. Most of the moisture in the region is frozen.
Conditions typical of Arctic lands are extreme fluctuations between summer and winter temperatures; permanent snow and ice in the high country and grasses, sedges, and low shrubs in the lowlands; and permanently frozen ground (permafrost), the surface layer of which is subject to summer thawing. Three-fifths of the Arctic terrain is outside the zones of permanent ice. The shortness of the Arctic summer is partly compensated by the long daily duration of summer sunshine.
The tropical climate provides varying amounts of rainfall—from 83 inches (211 centimeters) in the northwest to 14 inches (36 centimeters) in the southwest. The drought-prone south is extremely arid, and the west is hot and wet. Indian Ocean cyclones bring periodic heavy rains and destructive floods.
The hot, wet season extends from November to April and the cooler, drier season from May to October. The trade winds, which blow throughout the year, are strongest from May to October. The east coast is to the windward and has a high annual rate of precipitation, reaching nearly 150 inches (3,800 mm) at Maroantsetra on the Bay of Antongil. As the winds cross the plateau, they lose much of their humidity, causing only drizzle and mists on the plateau itself and leaving the west in a dry rain shadow. The southwest in particular is almost desert, with the dryness aggravated by a cold offshore current.
The monsoon, bringing rain to the northwest coast of Madagascar and the plateau, is most noticeable during the hot, humid season. The wind blows at an angle onto the west coast, which receives a moderate amount of precipitation annually; the southwest, which is protected, remains arid (dry). Annual precipitation drops from about 80 inches (about 2,000 mm) on the northwestern island of Nosy Be to about 40 inches (1,000 mm) at Maintirano on the west coast to about 14 inches (360 mm) at Toliara in the southwest. The plateau receives moderate levels of precipitation, with about 50 inches (1,200 mm) falling annually at both Antananarivo and Fianarantsoa, which lies about 200 miles (320 km) farther south.
July is the coolest month, with mean monthly temperatures around the island ranging from the low 50s F (low 10s C) to the high 70s F (mid-20s C), and December is the hottest month, with temperatures between the low 60s and mid-80s F (mid 10s and high 20s C). Temperatures generally decrease with elevation, being highest on the northwest coast and lowest on the plateau.
Tropical cyclones are an important climatic feature. They form far out over the Indian Ocean, especially from December to March, and approach the eastern coast, bringing torrential rains and destructive floods.
Australia has a wide range of tropical and mid-latitude climates, though it lacks the high mountain ranges that diversify the weather and climate patterns on other continents. It is generally quite hot and dry. Australia receives less precipitation than any other continent except Antarctica—an annual average of only 16.5 inches (42 centimeters), with half of the continent receiving less than 12 inches (30 centimeters) per year.
Australia's eastern and southern coasts (where Melbourne is), are dominated by mid-latitude climates such as Mediterranean, humid subtropical, and coastal maritime climates. They experience lesser temperature ranges and more reliable rainfall. Precipitation in these areas averages 40 to 60 inches (100 to 150 centimeters) each year. Although most of the precipitation comes from rain, snow covers many of the eastern mountains in the winter. Only at these higher elevations do winter temperatures compare with those commonly experienced in North America and Northern Europe. In low-lying areas summer temperatures average about 64° F (18° C), compared with winter temperatures of about 50° F (10° C).
Melbourne and its surroundings enjoy a mild climate but are periodically jolted by hot northerly winds alternating with cold southwesterlies. However, seasonal differences are not great, and winter in Melbourne seems like autumn or spring in North America or Europe. The average daily maximum temperatures range from 55° F (13° C) in July to 79° F (26° C) in January.
Lying to the northeast of continental North America and almost wholly within the Arctic Circle, Greenland is subject to intense cold and terrible blizzards. Glaciers flow from Greenland's icy mountains and discharge a billion tons of ice into the sea every year. Many of these enormous icebergs are carried into the lanes of ocean travel. The Jakobshavn Glacier, often moving 100 feet (30 meters) a day, is among the world's fastest glaciers.
Greenland's major physical feature is its massive ice sheet, which is second only to Antarctica's in size. The ice sheet reaches a maximum thickness of about 10,000 feet (3,000 meters) and covers more than 700,000 square miles, or nearly 85 percent of Greenland's total land area.
Some sections of Greenland have enough soil and warmth to support tundra vegetation and small trees. In general, however, the climate of Greenland is bleak and Arctic. Seven species of land mammals—polar bears, musk-oxen, reindeer, Arctic foxes, snow hares, ermines, and lemmings—can be found on the island. Seals and whales are found in the surrounding waters and were formerly the chief source of nourishment for the Greenlanders. Cod, salmon, flounder, and halibut are important saltwater fish, and the island's rivers contain salmon and trout.
The climate of Greenland is Arctic, modified only by the slight influence of the Gulf Stream in the southwest. Rapid weather changes, from sunshine to impenetrable blizzards, are common. Average winter (January) temperatures range from the low 20s F (about -7 °C) in the south to approximately -30 °F (about -34 °C) in the north. Summer temperatures along the southwestern coast average in the mid-40s F (about 7 °C) during July, while the average in the far north is closer to 40 °F (about 4 °C). Greenland experiences about two months of midnight sun during the summer. Average annual precipitation decreases from more than 75 inches (1,900 mm) in the south to about 2 inches (50 mm) in the north. Large areas of the island can be classified as Arctic deserts because of their limited precipitation. In the late 20th and early 21st centuries, scientists posited that global warming was profoundly affecting not only Greenland's climate but also its physical geography. A number of scientists noted, for example, that Greenland's vast ice sheet was shrinking at a highly increased rate.
The Icelandic climate is rather moderate despite the island's northerly latitude because of the relatively warm North Atlantic Drift waters that bathe the southern and western coasts. Nevertheless, the climate is cool throughout the year. The mean temperature at Reykjavík in January is 31° F (–0.6° C) and 52° F (11.2° C) in June. The northern coasts (where Nupur is) have colder water offshore for most of the year and the temperature there is normally 5.5° F (3° C) colder than the southern coast temperature in summer and 9° F (5° C) colder in winter. Along the northern coast drift ice and foggy conditions sometimes prevail during winter. The frost-free growing period is short, however, and snow remains at higher altitudes for six months or more.
Snow falls about 100 days per year in the northwest, about 40 in the southeast. Annual precipitation ranges from 16 inches (410 mm) on some high northern plateaus to more than 160 inches (4,100 mm) on the southern slopes of some ice-capped mountains. In the south it averages about 80 inches (2,000 mm). Gales are frequent, especially in winter, and occasionally heavy fog may occur, but thunderstorms are rare. Although winters are fairly dark, Reykjavík averages nearly 1,300 hours of bright sunshine a year. Often the aurora borealis (Northern Lights) is visible, especially in fall and early winter.