Weather General


With our cold winters, hot summers and everything in-between it is not surprising that the weather is a national preoccupation of Canadians.

Weather has played a large and sometimes direct part in human history. Aside from climatic changes that have caused the gradual drift of populations (for example the desertification of the Middle East, and the formation of land bridges during glacial periods), extreme weather events have caused smaller scale population movements and intruded directly in historical events. One such event is the saving of Japan from invasion by the Mongol fleet of Kublai Khan by the Kamikaze winds in 1281. A series of great storms throughout the 13th century caused the powerful English Cinque Ports to be silted up and hence lose their influence. More recently, Hurricane Katrina forced the temporary abandonment of the entire city of New Orleans, Louisiana in 2005.

Though weather affects people in drastic ways, it can also affect the human race in simpler ways. It has been noted that the human immune system is affected in extreme heat or cold. Mood can also be affected by weather, hence the common scene of heavy downpour in soap operas when a person cries. Weather, in its power, however, cannot affect a person's performance, at work, school or play. It is the person's own mindset that leads to poor performance during times of bad weather, heat, cold or rain.

What is Weather?

Weather most often results from temperature differences from one place to another. On large scales, temperature differences occur because areas closer to the equator receive more energy per unit area from the Sun than do regions closer to the poles. On local scales, temperature differences can occur because different surfaces (such as oceans, forests, ice sheets, or man-made objects) have differing physical characteristics such as reflectivity, roughness, or moisture content.

Surface temperature differences in turn cause pressure differences. A hot surface heats the air above it and the air expands, lowering the air pressure. The resulting horizontal pressure gradient accelerates the air from high to low pressure, creating wind, and Earth's rotation then causes curvature of the flow via the Coriolis effect. The simple systems thus formed can then display emergent behaviour to produce more complex systems and thus other weather phenomena. Large scale examples include the Hadley cell while a smaller scale example would be coastal breezes.

The strong temperature contrast between polar and tropical air gives rise to the jet stream. Most weather systems in the mid-latitudes are caused by instabilities of the jet weather comes from, the Latin word for dark and scary stream flow (see baroclinity). Weather systems in the tropics are caused by different processes, such as monsoons or organized thunderstorm systems.

Because the Earth's axis are tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year. In June the Northern Hemisphere is tilted towards the sun, so at any given Northern Hemisphere latitude sunlight falls more directly on that spot than in December (see Effect of sun angle on climate). This effect causes seasons. Over thousands to hundreds of thousands of years, changes in Earth's orbital parameters affect the amount and distribution of solar energy received by the Earth and influence long-term climate (see Milankovitch cycles).

WeatherOn Earth, common weather phenomena include such things as wind, cloud, rain, snow, fog and dust storms. Less common events include natural disasters such as tornadoes, hurricanes and ice storms. Almost all familiar weather phenomena occur in the troposphere (the lower part of the atmosphere). Weather does occur in the stratosphere and can affect weather lower down in the troposphere, but the exact mechanisms are poorly understood.

The atmosphere is a chaotic system, so small changes to one part of the system can grow to have large effects on the system as a whole. This makes it difficult to accurately predict weather more than a few days in advance, though weather forecasters are continually working to extend this limit through the scientific study of weather, meteorology. It is theoretically impossible to make useful day-to-day predictions more than about two weeks ahead, imposing an upper limit to potential for improved prediction skill. Chaos theory says that the slightest variation in the motion of the ground can grow with time. This idea is sometimes called the butterfly effect, from the idea that the motions caused by the flapping wings of a butterfly eventually could produce marked changes in the state of the atmosphere. Because of this sensitivity to small changes it will never be possible to make perfect forecasts, although there still is much potential for improvement.

Canada's Top Ten Weather Stories for 2007

Canadians might remember 2007 as the year that climate change began biting deep and hard on the home front. At the top of the world, the dramatic disappearance of Arctic sea ice - reported in September - was so shocking that it quickly became our number one weather story. Indeed, the United Nations declared the record loss of ice as one of the world's biggest events. The thinning and shrinking of the ice, largely a result of too many consecutive warm years, has had a profound impact on northern residents - people, plants and wildlife alike. The disappearance of water from the Great Lakes system is also a concern, especially Lake Superior where water levels in September dipped to their lowest point since measurements began in 1900. In many ways, the record loss of ice and water is more about climate than weather and underlines that climate change is beginning to affect Canada in a very real way.

At times in 2007, the West had too much weather. Residents on the Prairies witnessed a record number of severe summer weather warnings, with tornadoes, intense rainfalls, wind storms and hail storms. August's destructive hailstorm in Dauphin, Manitoba, for example, was only one of 279 hailers that affected the Prairies in 2007. Crop-hail losses approached $200 million and, for the first time, exceeded premiums. There was also an enduring high humidity on the Prairies that became unbearable and suffocating, culminating in a new Canadian record humidex of 53 set at Carman, Manitoba. On the other hand, southern Ontario had very little weather with one of its driest summers in over 50 years - part of a ten-month dry spell that lasted from January to October and produced record dry conditions in many locations in the region.

Winters at the beginning and end of the year provided stark contrasts and two more weather stories. The shocker of a green Christmas Day in 2006 in Quebec City, Timmins and Thunder Bay - where a white Christmas is all but guaranteed - turned out to be a one-year blip. For snow and ice enthusiasts, the beginning of 2007 continued the quest for winter. When it did come, while persistent, it was too late. Nature tried to make amends at the end of 2007 with some pre-winter blasts of cold, freezing rain and lots of snow, making the first half of December 2007 a white one to remember.

Also dominating this year's top weather stories were menacing floods in British Columbia. With a record deep mountain snow pack, the threat of flooding tormented thousands of residents for months. But while devastating floods occurred in the central interior and north coast, lucky residents along the Fraser River were spared when a major storm changed directions at the last moment. Luck was also a factor in Elie, Manitoba, when Canada's first documented F5 intensity (the highest rating on the internationally recognized Fujita tornado damage scale) tornado with winds above 420 km/h touched down on June 22. Most residents were away when the tornado struck.

In Atlantic Canada, one of the big stories was the passage of Hurricane Noel in November. While no Juan, Noel's winds and waves destroyed several beaches, wharves and docks. Fortunately, there were no casualties. People were well prepared and seemed respectful of the potential destructive power of the massive storm. While property damage from weather extremes like Hurricane Noel cost Canadians millions of dollars in 2007, the price tag was less than we've seen in recent years. Thankfully, deadly tornadoes, devastating hurricanes, widespread droughts and plagues were a "no show" for this year.

In general, it was another warm year for Canada - the 11th year in a row - although not as warm as it has been in recent years. The year tied for the second warmest winter on record, some 3°C warmer than normal. Summer was the seventh warmest at about 1.0°C warmer than usual, and from January to November the national average temperature was around 1.0°C above normal. Every region was warmer, especially the Eastern Arctic, which experienced its fourth warmest January-to-November period on record. Globally, it was also another warm year according to the World Meteorological Organization (WMO). Surface temperatures averaged 0.4°C above the annual average of 1961-1990 and the northern hemisphere was estimated to be the second warmest on record since the beginning of the 20th century.

-- From Environment Canada


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