FA - see Forecast Area

FAA - see Federal Aviation Administration

Fahrenheit Scale - a temperature scale on which the boiling point of water is at 212 degrees above the zero of the scale and the freezing point of water is at 32 degrees above zero

Fallstreak - same as Virga. Streaks or wisps of precipitation falling from a cloud but evaporating before reaching the ground. In certain cases, shafts of virga may precede a microburst.

Far Infrared - the region of the electromagnetic spectrum with wavelengths greater than infrared but shorter than microwaves; radiation between about 4 microns and 0.1 millimeters

FASTST - fastest

FCST - see Forecast

Federal Aviation Administration (FAA) - a Department of Transportation agency that regulates and oversees all aspects of civil aviation in the U.S.

Feeder Bands - lines or bands of low-level clouds that move (feed) into the updraft region of a thunderstorm, usually from the east through south (i.e., parallel to the inflow). Also known as inflow bands. In tropical meteorology, this term describes spiral-shaped bands of convection surrounding, and moving toward, the center of a tropical cyclone.

Ferrel Cell - in the general circulation of the atmosphere, the name given to the middle latitude cell marked by sinking motion near 30 degrees and rising motion near 60 degrees latitude

FFD - see Forward Flank Downdraft

FFG - see Flash Flood Guidance

FG - see Fog

Fine Line - see Thin Line

First Law of Thermodynamics - the law of physics that states that the heat absorbed by a system either raises the internal energy of the system or does work on the environment

FL - Florida

Flanking Line - a line of cumulus or towering cumulus clouds connected to and extending outward from the most active part of a supercell, normally on the southwest side. The line normally has a stair-step appearance, with the tallest clouds closest to the main storm.

Flash Flood - a local flood of great volume and short duration generally resulting from heavy rainfall in the immediate vicinity

Flash Flood Guidance (FFG) - forecast guidance specific to flash flooding

FLG - falling

Flood - the condition that occurs when water rises and overflows the natural or artificial confines of a body of water onto normally dry land, or accumulates in low-lying areas

FLRY - see Flurry

Fluid - matter that flows; a gas or a liquid

Flurry (or flurries) (FLRY) - light snowfall that generally does not produce measurable accumulation.

Flux - the amount of flow per unit time (i.e., energy flux or radiation flux)

FLW - follow

FM - fathom

FM - from

FNT - see Front

FNTGNS - see Frontogenesis

FNTLYS - see Frontolysis

Foehn - a warm, dry wind on the lee side of a mountain range. The warmth and dryness of the air is due to adiabatic compression as the air descends the mountain slopes. A Chinook is the name for Foehn winds in the Rocky and Sierra mountains.

Fog (FG) - a cloud with its base in direct contact with the ground

Force - mass times acceleration; the ability to change an object’s state of rest or motion

Forecast (FCST) - a statement predicting that an event will occur

Forecast Area (FA) - a specific area over which the conditions stated in a weather forecast are valid.

Forecast Guidance - computer-generated forecast materials used to assist the preparation of a forecast

Forward Flank Downdraft (FFD) - the main region of downdraft in the forward, or leading, part of a supercell, where most of the heavy precipitation occurs

FOUS - Forecast Output United States

FQT - frequent

Fractional Water Index (FWI) - (0=driest, 1=wettest) as soil moisture increases (soil gets wetter), the FWI increases as well. For completely saturated soil (can’t hold any more water) the FWI is close to 1.0. A powder-dry soil has an FWI near zero. The Oklahoma Mesonet soil moisture is shown as an FWI.

Fractus - see Scud, Cumulus Fractus, or Stratus Fractus

Free Atmosphere - the part of the atmosphere that lies above the frictional influence of the earth’s surface.

Freeze (verb) - to solidify as a result of heat removal

Freeze (noun) (FRZ) - a condition that occurs over a widespread area when the surface air temperature remains below freezing (below 32°F) long enough to damage agricultural crops

Freezing Drizzle (ZL) - drizzle that falls as liquid water but freezes upon impact to form a coating of ice upon the ground and on exposed objects

Freezing Precipitation - liquid precipitation that freezes upon impact with the ground or exposed objects (freezing rain or freezing drizzle).

Freezing Rain (FZRA, ZR) - rain that falls as liquid water but freezes upon impact to form a coating of ice upon the ground and on exposed objects

Frequency - the rate at which an event will reoccur; the reciprocal of the period. In radiation, the number of wave crests that pass by a point each second, described in hertz.

Friction - the mechanical resistive force of one object on another object’s relative movement when in contact with the first object

Friction Layer - same as Planetary Boundary Layer

FRMG - forming

Front (FNT) - the boundary or transition zone between two dissimilar air masses

Frontal Inversion - a temperature inversion in the atmosphere resulting from the vertical boundary between two air masses along a sloping front

Frontal Passage (FROPA) - the movement of a front across an area; characterized by changes in temperature, pressure, wind direction and speed, visibility, cloudiness and precipitation

Frontal Zone - a transition zone between air masses with different temperature and moisture characteristics.

Frontogenesis (FNTGNS) - the process of front formation. This occurs when there is an increase in the temperature gradient across a front.

Frontolysis (FNTLYS) - the process of front dissipation. This occurs when the temperatures and pressures equalize across a front.

FROPA - see Frontal Passage

FROSFC - frontal surface

Frost (FRST) - the formation of ice crystals on the ground or other surfaces under conditions similar to dew, except the temperature and dew point of the Earth’s surface and earthbound objects fall below 36°F.

Frostbite - the freezing or local effect of partial freezing of some part of the body

Frost Point - dew point below freezing

Frozen Dew - when liquid dew changes into tiny beads of ice. This occurs when dew forms and temperatures later drop below freezing.

Frozen Precipitation - precipitation that reaches the ground in frozen form. Examples include snow, snow pellets, snow grains, ice crystals, ice pellets (sleet), and hail.

FRST - see Frost

FRZ - see Freeze

FRZN - frozen

F Scale - see Fujita Scale

FTHR - further

Fujita Scale (F Scale) - the old scale used to classify the strength of a tornado. It was devised by Dr. Theodore Fujita from the University of Chicago and was originally created to smoothly connect the Beaufort and Mach Scales. It has been replaced by the Enhanced Fujita Scale (EF Scale).

Fujiwhara Effect - when two rotating systems (e.g., lows or tropical cyclones) rotate around each other. It is similar to a spinning teacups ride--each teacup spins independently, while all of the teacups move in a large circle

Funnel Cloud - a rotating cloud column or inverted cloud cone extending downward from a cloud base that is not in contact with the ground

Fusion - the phase change from a solid to a liquid; also known as melting.

FVRBL - favorable

FWD - forward

FWI - see Fractional Water Index

FZRA - see Freezing Rain