Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

F Scale

see Fujita Scale


FA

see Forecast Area


Fahrenheit Scale

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 microwavesradiation 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


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)

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 ScudCumulus Fractus, or Stratus Fractus


Free Atmosphere

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


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


Freeze (verb)

to solidify as a result of heat removal


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

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 temperaturepressurewind direction and speedvisibilitycloudiness 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.


Frost Point

dew point below freezing


Frostbite

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


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 snowsnow pelletssnow grainsice crystalsice pellets (sleet), and hail.


FRST

see Frost


FRZ

see Freeze


FRZN

frozen


FTHR

further


Fujita Scale (F Scale)

the 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) on February 1, 2007. Tornadoes before this date retain their F Scale value and have not been converted to the EF Scale. All tornadoes after February 2007 are assigned an EF Scale value. 

 

 

 

F0

Weak

40 - 72 mph

Light damage

F1

Weak

73 - 112 mph

Moderate damage

F2

Strong

113 - 157 mph

Considerable damage

F3

Strong

158 - 206 mph

Severe damage

F4

Violent

207 - 260 mph

Devastating damage

F5

Violent

261 - 318 mph

Incredible damage


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


FZRA

see Freezing Rain