Ch. 30 Weather Forecasting

What is weather?

The short term conditions of the atmosphere.

What is climate?

Climate is the average weather conditions in a place over a long period of time.

What instrument is used to measure temperature?

Maximum and minimum thermometer in °

What instrument is used to measure air pressure?

Barometer in millibars (mb)

What instrument is used to measure Humidity and relative humidity?

A wet and dry bulb thermometer in percentage relative humidity (%RH)

What instrument is used to measure precipitation?

Rain gauge in millimetres (mm)

What instrument is used to measure Wind direction

Wind vane with compass directions

What instrument is used to measure Wind speed?

Anemometer in Kilometers per Hours (km/hr)

What instrument is used to measure Sunshine hours and intensity?

Campbell- Stokes sunshine recorder in hours.

What instrument is used to measure Cloud cover

Observing it and using the oktas scale

Describe what a Stevenson Screen is.

A Stevenson Screen is a white, slatted box used in meteorology to hold weather instruments. It protects them from direct sunlight and rain while allowing air to flow in, helping ensure accurate temperature readings. It usually contains thermometers and a barometer.

Describe how a wet and dry bulb thermometer works. Draw a diagram.

A wet and dry bulb thermometer (hygrometer) measures humidity as relative humidity (% RH). It has two thermometers: one dry and one with a wet muslin-covered bulb. Evaporation from the wet bulb cools it. If air is saturated with water vapour, the water will not evaporate, giving the temperature of saturated air . It is kept in a Stevenson screen. High % RH means rain is more likely if the air cools and condensation occurs.

Describe how an anemometer works with a diagram.

An anemometer is a weather instrument used to measure wind speed, with units typically in kilometres per hour (km/h) or knots. It has 3 cups on an axle. When the wind blows, the cups rotate—the stronger the wind, the faster the rotation. A meter attached to the anemometer counts the number of full rotations, which is then used to calculate the wind speed.

Describe how cloud cover is recorded.

Cloud cover is measured by observing how much of the sky is covered by clouds.

To measure cloud cover:

• Find a clear spot with a full view of the sky.

• Divide the sky into four quarters: north, east, south, and west.

• Each quarter is worth 2 oktas (1 okta = one eighth of the sky).

• Estimate how much cloud is in each quarter. For example, if half the quarter is cloudy, that’s 1 okta.

• Add up the oktas from all four quarters to get the total cloud cover.

What does this mean?

Warm front.

What does this mean?

Cold front.

What does this mean?

Depression.

What does this mean?

Occluded front

What does this mean?

Isobars showing air pressure

What does this mean?

Anticyclone