F
Temperature scale where water freezes at 32°F and boils at 212°F.
The temperature scale, developed by the German physicist Daniel Gabriel Fahrenheit in 1714, where water at the standard sea-level pressure of 1013.25 hPa has a freezing point of +32°F and a boiling point of +212°F.
The lines or bands of cumulonimbus clouds that spiral into and around the centre of a tropical cyclone.
Used to describe an amount of cloud covering the sky of one or two oktas (eighths). In aviation forecasts and reports it is coded as FEW.
Flooding that happens within about 6 hours of rain. It's usually the result of intense local rain and water levels rise rapidly.
When water covers land that is normally dry.
The tidal phase during which the water level is rising, or the tidal current is flowing inland (flood current). Opposite to ebb. See also streams.
Flat or nearly flat land subject to flooding that is next to a stream or river.
A warm and dry downslope wind descending the lee side of a mountain range.
Warm, dry wind generally blowing downslope on the lee side (sheltered from the wind) of a mountain.
A suspension in the air, at or near the earth’s surface, of microscopic water droplets, or wet hygroscopic particles, reducing horizontal visibility to less than 1000 metres. In aviation forecasts and reports it is coded as FG.
A factor used to characterise the tides in an area as being mainly diurnal, semi-diurnal, or mixed.
A two-week tide cycle. In most parts of the world, the tides go through a fortnightly spring–neap cycle. These are beat phenomena rather than actual harmonics.
There are also some harmonics arising directly from the tide-generating potential which have a period of a fortnight.
Supercooled drizzle (i.e. drizzle existing at a temperature below 0°C) that freezes upon impact with surfaces to form glaze. In aviation forecasts and reports it is coded as FZDZ.
The temperature at which a liquid solidifies under any given set of conditions. Pure water under the standard sea-level pressure of 1013.25 hPa freezes at 0°C (32°F).
Any form of supercooled precipitation that freezes upon impact with surfaces to form glaze.
Supercooled rain that falls as liquid but freezes upon impact with surfaces to form glaze. In aviation forecasts and reports it is coded as FZRA.
The mechanical resistive force offered by one medium or body to the relative motion of another medium or body in contact with the first. In meteorology, it is the drag or resistance of the earth on the atmosphere.
The thin layer of the lower atmosphere within which wind direction and speed is subject to frictional effects caused by contact with the earth’s surface. Its depth is variable, ranging from tens of metres in a stable environment, to several kilometres in convective conditions over deserts.
The boundary between air masses with different characteristics. See also:
The transition zone or interface between two air masses of different densities.
The passage of a front over a specific point on the earth’s surface. Changes in temperature, dew point, wind and atmospheric pressure occur with a frontal passage.
Soft white ice crystals or frozen dewdrops on objects near the ground. It forms when the surface temperature falls below freezing point.
Violent, rotating column of air extending toward the ground from the base of a cumulus or cumulonimbus cloud.
A funnel cloud that reaches the ground is called a tornado if over land, and a waterspout if over water.