F
Scale - see Fujita scale
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
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
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
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
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 - forecast guidance
specific to flash flooding
Flood
- the condition that occurs when water rises and overflows
the natural or artificial confines of a body of water on to normally dry
land, or accumulates in low-lying areas
Fluid
- matter which flows; a gas or a liquid
Flux
- the amount of flow per unit time (i.e. energy flux or radiation
flux)
Fog
- a cloud with its base in direct
contract with the ground
Force
- mass times acceleration; the ability to change an object's
state of rest or motion
Forecast
- a statement predicting an event will occur
Forecast
Guidance - computer-generated forecast materials used to assist
the preparation of a forecast
Forward
Flank Downdraft - the main region of downdraft
in the forward, or leading, part of a supercell,
where most of the heavy precipitation
occurs
Freeze
(verb) - to solidify as a result of removal of heat
Freeze
(noun) - a condition which occurs over a widespread area when
the surface air temperature remains below
freezing long enough to damage certain agricultural crops
Freezing
Drizzle - drizzle that falls as
liquid water but freezes
upon impact to form a coating of ice upon the
ground and on exposed objects
Freezing
Rain - 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
Front
- 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 - the movement of a front across an area; characterized
by changes in temperature, and, generally
in pressure, wind
direction and speed, visibility,
cloudiness and precipitation
Frost
- the condition which exists ice is
formed on the earth's surface when the temperature
falls below freezing
Frostbite
- the freezing or local effect
of partial freezing of some part of the body
Fujita
Scale - a scale for classifying tornadoes
according to the damage they cause; the tornado's rotational wind speed
is inferred from an analysis of the wind damage
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
|
Funnel
Cloud - a rotating cloud column or inverted cloud cone extending
downward from a cloud base that is not in contact with the ground
|