F

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 center 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.

Foothills - The locations along the west of Denver are considered to be areas with elevations between 6,000 and 9,000 feet above Sea Level. The foothills include towns and cities such as Evergreen, Conifer, Georgetown, Idaho Springs, Estes Park, Nederland, Fairplay, etc.
The southern suburbs of Denver have some areas that get up to about 6,000 feet in elevation and they also can have weather conditions similar to foothills locations due to the enhanced effect the terrain has on increasing local precipitation - but these areas are not technically considered to be "in the foothills".

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 rearrear 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 tornado that hasn't reached the ground. It appears as a rotating, cone like cloud that extends out of the base of a thunderstorm. 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.