Glossary and Acronyms: F

FF10:

10-min average wind speed. This the wind speed usually used in meteorology. American use a 1-min average wind speed. FF10min = 0.88 FF1min and FF gust = 1.41 FF10min. See also Wind speed.

Fahrenheit:

(degree, symbol °F). Unit of temperature use by the American. Conversion to the Celsius temperature scale (C) is accomplished by the formula F = 32+1.8C (or C= (F-32)5/9).

FASTEX:

Fronts and Atlantic Storm-Track Experiment. FASTEX is an international research project about weather, precisely about mid-latitude cyclone depressions.

Fetch:

distance along a large water surface trajectory over which a wind of almost uniform direction and speed blows.

Flat low:

Depression whose horizontal pressure gradient is weak.

Fmax:

maximum speed of the instantaneous wind (maximum gust).

FNMOC:

Fleet Numerical Meteorology and Oceanography Center (US Navy).

Severe tropical storm:

tropical system in which the maximum of the 10-min average wind speed is estimated to be in the range 48 to 63 knots (89 to 117 km/h, force 10 or 11 in the Beaufort scale). See also FAQ A3.

Forecast error (track):

a measure of the difference between a forecast tropical system centre fix and the corresponding verification from analysis or observations.
The RSMC La Réunion mean track forecast errors for the season 2008-2009 are:

Range	00	12	24	36	48	60	72
Mean (km)	33	85	121	151	181	220	269

For further informations, see section "Forecast Accuracy"

Four-dimensional variational data assimilation (4D-Var):

process that merges data from different sources and types but as well data observed at different times.
4D-Var analysis determines initial values, convenient for a numerical weather prediction model which uses data distributed in time as well as in space (in contrast with methods using only synoptic data).

Front:

in meteorology, generally, the interface or transition zone between two air masses of different density (temperature, density). Along with the basic density criterion and the common temperature criterion, many other features may distinguish a front, such as a pressure trough, a change in wind direction, a moisture discontinuity, and certain characteristic cloud and precipitation forms. The term front is used ambiguously for 1) frontal zone, the three- dimensional zone or layer of large horizontal density gradient, bounded by 2) frontal surfaces across which the horizontal density gradient is discontinuous (frontal surface usually refers specifically to the warmer side of the frontal zone); and 3) surface front, the line of intersection of a frontal surface or frontal zone with the earth's surface.
A cold front is any nonoccluded front, or portion thereof, that moves so that the colder air replaces the warmer air; that is, the leading edge of a relatively cold air mass.

FSU:

Florida State University.

Fujita scale:

also known as the F-scale. Relates tornado intensity indirectly to structural and/or vegetative damage.
The estimated wind speed is calculated using the following formula: V = 6.30 (F+2)^1.5 ms^-1. A six-point scale has been developed that corresponds to the following wind-speed estimates:

F0 (light damage): 18-32 ms^-1
F1 (moderate damage): 33-49 ms^-1
F2 (considerable damage): 50-69 ms^-1
F3 (severe damage): 70-92 ms^-1
F4 (devastating damage): 93-116 ms^-1
F5 (incredible damage):117-142 ms^-1.

Although extremely dependent on the design of a structure and the tree type, the following visual characteristics of the damage have been assigned to the F-scale.

F0 - Some damage to chimneys; branches broken; shallow-rooted trees knocked over.
F1 - Surface of roofs peeled off; mobile homes pushed off foundations or overturned; moving autos pushed off road.
F2 - Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted.
F3 - Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off ground and thrown.
F4 - Well-constructed houses leveled; structures with weak foundations blown off; large missiles generated.
F5 - Strong frame houses lifted off foundations and carried considerable distances; automobile- sized missiles flying through the air for distances in excess of 100 m; trees debarked.

Fujiwhara effect:

the tendency of two nearby tropical systems to rotate cyclonically about each other (around a translating point between them) as a result of their circulations' mutual advection.

FY:

Feng Yun. A general name (translated as "wind and cloud," frequently abbreviated FY) for several series of meteorological satellites maintained by the People's Republic of China.
The FY-1 series of sun-synchronous, polar-orbiting satellites was initiated with the launch of experimental satellites in 1988 and 1990. The first operational satellite in this series (FY-1C) was launched in May 1999. The FY-1C and FY-1D satellites have a 10-channel imaging instrument with four visible channels, three in the near-infrared, one in the short infrared, and two in the thermal infrared.
A separate series of geostationary meteorological satellites, designated FY-2, are positioned at 105°E longitude. The first satellite in this series was launched in June 1997. The most recent Satellite FY-2D, with capabilities similar to the Japanese GMS-5, was launched in 2007.
(Link to the Chinese Meteorological Administration).