Subj : Wx Terms (F)(4)
To   : All
From : Daryl Stout
Date : Sat Oct 07 2017 12:04 am

Fountainhead
In hydrologic terms, the upper end of a confined-aquifer conduit, where
it intersects the land surface.

FOUS
Forecast Output United States

FPO
Flood Potential Outlook

FPS
Fujita-Pearson Scale

FQT
Frequent

Fractocumulus
A cumulus cloud presenting a ragged, shredded appearance, as if torn.

Fractostratus
A stratus cloud presenting a ragged, shredded appearance, as if torn. It
differs from a fractocumulus cloud in having a smaller vertical extent
and darker color.

Fracture
In hydrologic terms, any break or rupture formed in an ice cover or floe
due to deformation.

Fracture Zone
In hydrologic terms, an area which has a great number of fractures.

Fracturing
In hydrologic terms, deformation process whereby ice is permanently
deformed, and fracture occurs.

Fractus
Ragged, detached cloud fragments; same as scud.

Frazil Ice
In hydrologic terms, fine spicules, plates, or discoids of ice suspended
in water. In rivers and lakes, frazil is formed in supercooled, turbulent
water.

Frazil Slush
In hydrologic terms, an agglomerate of loosely packed frazil which floats
or accumulates under the ice cover.

Freak Wave
A wave of much greater height and steepness than other waves in the
prevailing sea or swell system. See Rogue Wave.

Free Atmosphere
The part of the atmosphere that lies above the frictional influence of
the earth's surface.

Free Ground Water
In hydrologic terms, unconfined ground water whose upper boundary is a
free water table.

Freeboard
In hydrologic terms, the vertical distance between the normal maximum
level of the water surface in a channel, resrvoir, tank, canal, etc.,
and the top of the sides of a levee, dam, etc., which is provided so
that waves and other movements of the liquid will not overtop the
confining structure.

Freeze
A freeze is when the surface air temperature is expected to be 32�F or
below over a widespread area for a climatologically significant period
of time. Use of the term is usually restricted to advective situations
or to occasions when wind or other conditions prevent frost. "Killing"
may be used during the growing season when the temperature is expected
to be low enough for a sufficient duration to kill all but the hardiest
herbaceous crops.

Freeze Warning
Issued during the growing season when surface temperatures are expected
to drop below freezing over a large area for an extended period of time,
regardless whether or not frost develops.

Freezeup date
In hydrologic terms, the date on which the water body was first observed
to be completely frozen over.

Freezing Drizzle
A drizzle that falls as a liquid but freezes into glaze or rime upon
contact with the cold ground or surface structures.

Freezing Drizzle Advisory
Issued when freezing rain or freezing drizzle is forecast but a
significant accumulation is not expected. However, even small amounts
of freezing rain or freezing drizzle may cause significant travel
problems.

Freezing Fog
A suspension of numerous minute ice crystals in the air, or water
droplets at temperatures below 0� Celsius, based at the Earth's surface,
which reduces horizontal visibility; also called ice fog.

Freezing Level
The altitude at which the air temperature first drops below freezing.

Freezing Rain
Rain that falls as a liquid but freezes into glaze upon contact with
the ground.

Freezing Rain Advisory
Issued when freezing rain or freezing drizzle is forecast but a
significant accumulation is not expected. However, even small amounts
of freezing rain or freezing drizzle may cause significant travel
problems.

Freezing Spray
An accumulation of freezing water droplets on a vessel caused by some
appropriate combination of cold water, wind, cold air temperature, and
vessel movement.

Freezing Spray Advisory
An advisory that may be issued within the Offshore Waters Forecast,
the Coastal Waters Forecast, the Nearshore Marine Forecast, and the
Open Lake Forecast (GLF). An accumulation of freezing water droplets
on a vessel at a rate of less than 2 centimeters (cm) per hour caused
by some appropriate combination of cold water, wind, cold air
temperature, and vessel movement.

Freezup jam
In hydrologic terms, ice jam formed as frazil ice accumulates and
thickens.

French Drain
In hydrologic terms, an underground passageway for water through the
interstices among stones placed loosely in a trench.

Freshet
The annual spring rise of streams in cold climates as a result of snow
melt; freshet also refers to a flood caused by rain or melting snow.

Friction
The mechanical resistive force of one object on another object's
relative movement when in contact with the first object. In meteorology,
friction affects the motion of air (wind) at and near the Earth's
surface.

Friction Head
In hydrologic terms, the decrease in total head caused by friction.

Friction Layer
Same as Planetary Boundary Layer; the layer within the atmosphere
between the earth's surface and 1 km above the surface; this is the
layer where friction affects wind speed and wind direction.

FRMG
Forming

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.

Frontal Inversion
A temperature inversion that develops aloft when warm air overruns
the cold air behind a front.

Frontogenesis

1. The initial formation of a front or frontal zone.

2. In general, an increase in the horizontal gradient of an airmass
property, principally density, and the development of the accompanying
features of the wind field that typify a front.

FROPA
Frontal Passage

FROSFC
Frontal Surface

Frost
(Abbrev. FRST) - Frost describes the formation of thin ice crystals on
the ground or other surfaces in the form of scales, needles, feathers,
or fans. Frost develops under conditions similar to dew, except the
temperatures of the Earth's surface and earthbound objects falls below
32�F. As with the term "freeze," this condition is primarily significant
during the growing season. If a frost period is sufficiently severe to
end the growing season or delay its beginning, it is commonly referred to
as a "killing frost." Because frost is primarily an event that occurs as
the result of radiational cooling, it frequently occurs with a thermometer
level temperature in the mid-30s.

Frost Advisory
Issued during the growing season when widespread frost formation is
expected over an extensive area. Surface temperatures are usually in the
mid 30s Fahrenheit.

Frost Point
Dew point below freezing.



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