F scale - See Fujita Scale.
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). Same as inflow bands.
This term also is used in tropical meteorology to describe
spiral-shaped bands of convection surrounding, and moving toward,
the centre of a tropical cyclone.
*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, and generally coincides with the pseudo-cold front.
Forward Flank Downdraft - The main region of downdraft in the
forward, or leading, part of a supercell, where most of the heavy
precipitation is. Compare with rear flank downdraft.
Front - A boundary or transition zone between two air masses
of different density, and thus (usually) of different temperature. A
moving front is named according to the advancing air mass, e.g.,
cold front if colder air is advancing.
Fractus - Ragged, detached cloud fragments; same as scud.
Fujita Scale (or F Scale) - A scale of wind damage intensity
in which wind speeds are inferred from an analysis of 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, (rare) incredible damage.
All tornadoes, and most other severe local windstorms, are assigned
a single number from this scale according to the most intense damage
caused by the storm.
*Funnel Cloud - A condensation funnel extending from the base
of a towering cumulus or Cb, associated with a rotating column of
air that is not in contact with the ground (and hence different from
a tornado). A condensation funnel is a tornado, not a funnel cloud,
if either a) it is in contact with the ground or b) a debris cloud
or dust whirl is visible beneath it.