F
The terms and definitions found in the glossary relate to the science of meteorology.
For descriptions and definitions of words used in the Bureau's forecasts and warnings, please refer to Weather Words.
- Fahrenheit temperature scale
- Thermodynamic scale of temperature. Temperature in degrees Fahrenheit can be obtained from value in degrees Celsius by the following formula:
F = (9C/5) + 32 - Fine
- (As used by forecasters) No rain or other precipitation (hail, snow etc.). The use of fine is generally avoided in excessively cloudy, windy, foggy or dusty conditions. In particular note that fine means the absence of rain or other precipitation such as hail or snow - not 'good' or 'pleasant' weather.
- Flash Flood
- Flood of short duration with a relatively high peak discharge.
- Flood
- A flood occurs when water inundates (covers) land which is normally dry.
- Flood Forecasting
- Estimation of height, discharge, time of occurrence, and duration of a flood, especially of peak discharge, at a specified point on a stream, resulting from precipitation and/or snowmelt.
- Flood Warning
- Advance notice that a flood may occur in the near future at a certain location or in a certain river basin.
- Foehn
- (Similar in pronunciation to 'fern'.) Wind warmed and dried by descent, in general on the lee* side of a mountain. See the explanation and animation in Fig.1 below.
* The side away from the direction the wind is blowing from.
Fig.1
Air is forced to flow against and over a mountain range in a short period of time. The air cools as it rises up the mountain range, cloud forms and rain or snow falls. Heat is added to the air through condensation of water vapour (latent heat) thus reducing the rate at which the air cools. When the air descends on the other side it has lost some of its moisture (because rain and/or snow has fallen from it) and it is warmed by compression as it descends. This dry, warm wind is the foehn wind.
The windward side is usually very wet while the lee side can be a dry desert. Rainfall in Australia is greater in the east due to the influence of the Great Dividing Range. - Fog
- A dense mass of small water droplets or particles in the lower atmosphere.
- Forecasting Terms
- See Weather Words.
- Freeze
- Change from a liquid to a solid.
- Front
- The boundary between air masses having different characteristics.
- Front (Cold)
- In some regions along the polar front, cold dense air advances equatorwards, causing warm air to be forced aloft over its sloping surface. This portion of the polar front is known as a cold front.
Cold polar air is replacing warm tropical air. - Front (Warm)
- In other regions along the front, warm air of lower density moves polewards, sliding over its sloping surface. This portion is called a warm front.
Warm tropical air replaces cold polar air. - Front (Occluded)
- When the cold front moves faster than the warm front, and as it overtakes the warm front, the warm sector is closed and a combine front forms. This process is called occlusion.
The front formed in this way is called an occluded front.
- Frost
- Deposit of soft white ice crystals or frozen dew drops on objects near the ground; formed when surface temperature falls below freezing point.
See: About frost.