The weather is the daily atmospheric conditions consisting of precipitation,
temperature
humidity
wind
and sunshine.
These elements are variable throughout the course of the day.
For example, where I live in Auckland, it is often said that we have four seasons in one day.
One moment it can be sunny and warm. An hour later it can be wet and windy.
Precipitation refers to the moisture in the atmosphere
and can manifest itself as rain
snow
hail
sleet
or fog.
Sleet is actually rain and snow mixed.
That is snow fall that melts partially as it falls to the earth.
There are three main causes of precipitation:
Frontal precipitation takes place at the
boundaries of where two air masses of different densities meet.
For example, where a cold air mass meets a warm air mass.
Where the air meets the warm air is cooled and water vapor condenses, clouds form
and precipitation occurs.
Convectional precipitation is common in tropical areas.
It is caused when the intense Sun heats the ground
causing warm air to rise.
The air cools as it rises
causing water vapor to condense and into clouds
which eventually leads to precipitation.
These storms are often heavy but are over relatively quickly.
Orographic precipitation (Relief Rainfall) occurs when air masses are forced to rise over mountain ranges.
The air cools has as it is forced upwards.
As it cools the water vapor begins to condense and finally forces rain
As a consequence the windward side of a mountain range is wetter than the leeward side,
where there is a rain shadow area.
For example, the West Coast of the Southern Alps of New Zealand experiences a wet climate.
While the Canterbury plains east of the mountains have a drier climate.
Rainfall is measured in millimeters.
Humidity is the amount of water vapor in the air.
We measure humidity as a percentage.
Inland locations have dry air with a low average humidity of around 10 percent.
Coastal locations are more humid, with an average humidity of around 70 to 80 percent.
Wind is the movement of air.
Wind is caused by differences in air pressure.
It moves from areas of high pressure to areas of low pressure.
The force of wind is often measured in terms of wind speed.
One commonly used scale is the Beaufort scale which was based on observations of sea conditions.
A zero on the scale or calm air is wind speeds of less than one kilometer per hour for a 10 minute period.
At 12 on the scale we have hurricanes
with wind speeds in excess of 120 km/h.
For hurricanes there is a separate scale called the saffir-simpson scale.
This scale ranges from category 1 to category 5.
With a 5 category hurricane being the most destructive
with winds of over 252 kilometers per hour.
Wind direction is measured in terms of the direction wind is coming from.
For example in New Zealand we have prevailing southwesterly winds.
That means that the dominant wind pattern is winds coming from the southwest
and are heading and a northeasterly direction.
Sunshine is the amount of incoming solar radiation received at a particular location.
Sunshine is also known as insolation.
The amount of sunlight that a particular location receives
will depend on factors such as latitude
the weather
the seasons of the year
and the time of day
A given location receives its maximum amount of sunshine at noon
when the Sun is at its highest point in the sky.
In New Zealand the town of Blenheim
receives 2,500 hours of sunshine a year.
Invercargill by contrast only recieves 1600 hours.
Temperature refers to the heat in the atmosphere.
Temperatures vary both spatially and at different times.
Temperatures are generally warmer closer to the equator
and at low altitudes.
Temperatures are directly affected by sunlight hours.
From day to day temperatures are generally highest a few hours after mid day.
This is because the Earth absorbs the sunlight and re-radiates it out into the atmosphere, warming it up.
The coldest part of the day is just before sunrise.
In temperate climates, temperatures are generally coldest in winter when sunlight hours are shorter
and are warmest in summer when sunlight hours are longer.
There are different systems for measuring temperature.
The more commonly used systems are degrees Celsius and degrees Fahrenheit.
For example, the freezing point of water
is zero degrees Celsius or 32 degrees Fahrenheit.
Whereas the boiling point of water is 100 degrees Celsius or 212 degrees Fahrenheit.
Room temperature is 20 degrees Celsius or 68 degrees Fahrenheit.