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Weather Words - F
-- F --
Fahrenheit: A temperature scale (introduced by Gabriel Daniel Fahrenheit in
1714) in which the melting point of ice is 32 degrees and the boiling point
of water is 180 units higher, at 212 degrees.
Fahrenheit, Gabriel Daniel: (1686-1736) A German instrument maker who
(in 1714) invented the first mercury-in-glass thermometer and the scale of
temperature by which his name is daily remembered. He set the melting
point of ice at 32 degrees F and the boiling point of water 180 degrees
higher.
Fair: Descriptive of pleasant weather conditions, with due regard for the
location and time of year. In weather forecasts, it means no precipitation
and no extreme conditions of cloudiness, visibility or wind.
Fall speed: The speed with which precipitation particles (raindrops,
snowflakes, hail, etc.) fall through air. The fall speed for large raindrops
is up to about 30 feet per second, but much greater for hail.
Fall wind: Wind resulting from cold air moving downslope and accelerating
as it goes because of its low temperature and greater density.
Fallout: The radioactive debris from a nuclear explosion that falls back to
earth either of its own weight or that is brought down in rain and snow.
Radioactive debris can remain in the atmosphere for years.
Fallout pattern: The area downwind of a nuclear explosion that is covered
by dangerous radioactive debris. Because the mushroom and debris cloud
following a nuclear explosion rises many miles upward through varying
wind strata, forecasting the fallout pattern accurately would be difficult.
False spring: A period of late-winter or early-spring weather sufficiently
mild and prolonged to cause dormant vegetation to begin growing too
soon, making it vulnerable to frost and freeze damage.
Fast ice: (1) Sea or lake ice that is immobile due to its attachment to a
coast, and not to be confused with ice covering a frozen lake.
Fast ice: (2) Ice that extends seaward from land to which it is attached.
Fathom: The common unit of depth in the ocean for countries using the
English system of measurement. It is six feet or 1.83 meters. It is also
used in expressing horizontal distance, since 120 fathoms is nearly equal to
one-tenth of a nautical mile.
February: The 2nd month of the year and 3rd (and last) month of
meteorological winter. With a 77-year average temperature (Midway)
of 28.0 degrees F , precipitation of 1.59 inches and snowfall of 8.2 inches,
it is Chicago's 2nd coldest, its driest and 3rd snowiest month.
February 8, 1987: The most damaging ($7 million) lakeshore flooding and
erosion event in Chicago's history. North winds 50-70 m.p.h. drove 18-foot
waves onto the city shoreline. Water surged across Lake Shore Drive and
waves battered high-rise buildings on the city's North Shore.
February 11, 1935: The temperature at Ifrane, Morocco, plunged to
-11 degrees F, the lowest temperature ever recorded in Africa. In
1999, Chicago's temperature zoomed to 70, the city's earliest-occurring
spring temperature of 70.
Federal Emergency Management Agency (FEMA): A federal agency
whose mission is to reduce loss of life and property from all types of
hazards through mitigation, preparedness, response and recovery.
Feedback: A relationship between two components of a weather system such
that changes in one component cause changes in the other component which, in
turn, affect further change in the first component. An example: Drought
causes heat that strengthens drought.
Feeder bands: In thunderstorm development, the lines or bands of low-level
clouds that move into (or feed into) the updraft region of a thunderstorm.
Field ice: An ice pack so extensive on an ocean or large lake that its
limits cannot be seen from the vantage point of the viewer (on land or on a
ship).
Fetch: In general, the area in which waves are being generated by the wind;
more specifically, the length of the fetch area measured in the direction of
the wind.
Filtered sunshine: Jargon for sunlight through a layer of transparent clouds
(like cirrus) that barely reduces the intensity of the light or the
brightness of the day.
Fine: As used in weather forecasts in Australia, pleasant and settled
weather regarding temperature, wind and humidity; equivalent to fair in U.S.
forecast terminology.
Finley, U.S. Army Signal Corps Sergeant John Park: The first tornado
climatologist and forecaster. His pioneering efforts in the late 1800s were
the first attempts at serious national documentation of tornadoes. His
accomplishments were remarkable, given the technology and limited
understanding of severe storms.
Fire season: The time of year when vegetation is most likely to burn. The
threat of forest and grass fires in the Midwest is greatest in the early
spring (after snow has melted but before vegetation has greened up) and in
the late autumn (after vegetation has browned but before snow cover and cold
temperatures arrive).
Fire weather: The state of the weather with respect to its effect on the
kindling and spreading of forest fires. Fire-inducing conditions include
little or no precipitation in the days or weeks before the time in question,
and low humidity and high wind on the day in question.
Fireball: (1) A streak of light in the night sky so bright that it can cast
noticeable shadows. Meteoroids enter the Earth's atmosphere at speeds as
high as 150,000 m.p.h. and glow to incandescence, owing to friction with the
atmosphere.
Fireball: (2) The sphere of superheated, incandescent gas that forms
immediately after the detonation of a nuclear weapon. It can persist as long
as ten seconds after the blast.
Firenado: An intense tornado-like whirlwind that forms in the plume of
heated air rising above a large fire, made visible by smoke (and
occasionally flame, if the fire is large enough) drawn into the whirl.
Firestorm: A fire of such great size and intensity that the column of heated
air rising above it causes wind at ground level to blow from all directions
into the fire area with great speed, sometimes 30-60 m.p.h.
Firn: Old snow (usually more than one year) that has become granular, dense
and compacted mainly as a result of melting and refreezing. The resulting
particles are generally spherical and rather uniform.
Firnification: The process by which old snow is slowly transformed, mainly
by melting and refreezing, into a dense layer of granular, spherical and
compacted particles.
Five-hour hurricane: A hurricane moving so rapidly (sometimes in excess of
45 m.p.h.) that, at a given location, it arrives and departs within five
hours, rather than the more typical duration of 24-48 hours. Hurricanes that
strike New England often move very rapidly.
Flagged tree: A tree whose branches grow only to one side because of strong,
persistent prevailing winds (or other factors, such as salt spray from
oceans, that inhibit plant growth into the wind).
Flan: In Scotland, a sudden gust or squall of wind.
Flaw: A British nautical term for a sudden gust or squall of wind.
Flare: A bright, short-lived (hour or less) event in the uppermost layers of
the sun that produces greatly increased emissions of radiation (in radio
frequencies) and sometimes of particles as well.
Flash drought: Extreme but short-term (generally a few weeks) dryness, often
accompanied by well above-normal temperatures.
Flash flood: (1) Rapid flooding that occurs during or within several hours
of an intense rain. other causes are ice jams, dam failures, etc. Due to
the hazard the National Weather Service issues flash flood watches and
flash flood warnings. Over flat terrain, such as in Chicagoland, flash
flooding often takes the form of ponding of water in low-lying areas.
Flash flood: (2) A flood that rises and falls very rapidly with little or no
advance indication that it will occur, usually as the result of intense
rainfall over a relatively small area.
Flint, Mich., tornado disaster: On June 8, 1953, the most deadly tornado
ever to strike Michigan ravaged the city of Flint. Striking at about 8:30
p.m.
CDT, the violent F-5 tornado tore through Flint, killing 116 and injuring
785.
Flist: In Scotland, a sudden shower accompanied by squally winds. 11/24/05
Floe: A separate and relatively flat patch of floating, unbroken ice that is
greater than about 60 feet across. It may be composed of several fragments
of ice that are bonded together.
Flood: (1) A condition that occurs when water overflows the natural or
artificial confines of a river or other body of water, or accumulates by
drainage over low-lying areas.
Flood: (2) Temporary inundation of normally dry land from the overflow of
inland or tidal waters, or from the unusual and rapid accumulation of, or
runoff of, water from any source.
Flood, The: The universal deluge recorded in the Old Testament of the Bible
as having occurred during the life of Noah. Dates vary widely, but many
Biblical scholars place the occurrence at about 2,300 B.C.
Flood of record: At a given point on a river, the highest observed river
stage or greatest river discharge during the entire period of record
keeping.
Flood plain: The lowland that borders a river, usually dry but subject to
flooding when the river is high. Also, the portion of a river valley that
has been inundated by the river during historic floods. Flood-plain
development is always prone to flood damage.
Flood stage: The elevation of a river or stream surface at which overflow of
the normal banks begins to cause damage in the nearby upstream and
downstream areas to which that stage is applicable.
Floodproofing: Protecting a building from flood damage on site. In areas
subject to slow-moving and shallow flooding, buildings can be elevated or
barriers can be constructed to block the water's approach.
Floods and flash floods: A flash flood is rapid flooding that occurs
during or within a few hours of an intense rain. A flood develops gradually,
many hours or even many days after the rain event. The difference is in the
suddenness of their onset.
Florida: The lightning capital of the United States. Florida experiences
about 1.4 million lightning ground strikes per year, or about 25 ground
strikes per square mile annually.
Florida's highest temperature: 109 degrees F at Monticello (in the panhandle
of northern Florida) on Monday, June 29, 1931.
Florida's lowest temperature: -2 degrees F at Tallahassee on Monday, Feb.
13,
1899. With the exception of Hawaii (whose lowest temperature is 12), every
state has recorded a subzero temperature.
Florida's major hurricanes: Florida has sustained more direct strikes from
major hurricanes (storms containing winds of at least 111 m.p.h.) than any
other state. Of 66 major U.S. hurricanes in the period 1900-1999, 24 of
them (36 percent) struck Florida.
Foehn: A warm, dry wind on the lee (downwind) slopes of a mountain range.
The name originated in the Alps. Some local names: chinook of the Rocky
Mountains, zonda and puelche in the Andes. Rocky Mountains chinook winds
sometimes exceed 60 m.p.h.
Fog: A visible aggregate of water droplets suspended in the air at the
Earth's surface. Fog is literally a cloud on the ground. By definition,
dense
fog reduces horizontal visibility to 1/4 mile or less. Fog is reported in
aviation weather observations when it reduces horizontal visibility below
seven miles.
Fog bank: A fairly well-defined mass of fog observed at a distance, most
commonly at sea or over a very large lake. The term is not applied to
patches of shallow fog.
Fog drip: Water dripping to the ground from trees or other objects which
have collected the moisture from drifting fog. In some instances the
dripping is as heavy as steady light rain, as sometimes occurs among the
redwood trees of northern California.
Fog forest: The dense, rich forest growth that is found at high or
medium-high altitudes on tropical mountains. It occurs when the tropical
rain forest penetrates altitudes of cloud formation.
Forecast: A statement of expected future occurrences of the weather up
to 48 hours ahead, including such atmospheric variables as temperature,
precipitation, amount of cloudiness and wind direction and speed.
Forensic meteorology: The application of the science of meteorology to
the law. For example, forensic meteorologists can be called upon to
reconstruct weather events at a specific time and location when weather
is a factor in a criminal investigation.
Foreshore: On a lake, the part of the shore that lies between the high and
low water marks.
Forest wind: A light breeze that blows from forests toward open country on
clear calm nights. The main cooling at night in a forest takes place at the
tree tops; this cool air sinks through the trees and then flows outward
toward open ground.
Forked lightning: A common form of lightning in a cloud-to-ground
strike, that exhibits downward-directed branches from the main lightning
channel.
Fracto-: An adjective or prefix used in cloud nomenclature to denote a
ragged, broken structure; descriptive of clouds fragmented by strong winds:
fractocumulus, fractostratus.
Fractus: A word used to describe clouds broken into fragments by strong
winds -- such as stratus fractus or cumulus fractus. When used as a prefix,
the form fracto- is used, as in fractostratus or fractocumulus.
Frank, Dr. Neil, past director of the National Hurricane Center: "...We
should limit development along river valleys subject to flooding or on
small, sandy coastal islands exposed to devastating hurricanes. But we have
decided not to do that in this country, so we are extremely vulnerable to
storms."
Franklin, Benjamin: (1706-1970) American statesman, diplomat, author,
inventor and scientist who was the first person to establish the link
between volcanic eruptions and climatic cooling when he suggested the
bitterly cold winter of 1783-84 in Europe was a result of the dust cloud
from a massive eruption of Iceland's Mt. Laki in 1783.
Franklin, Benjamin kite experiment: It is believed that on June 10, 1752,
Benjamin Franklin narrowly missed electrocution while flying a kite during
a thunderstorm to determine if lightning is related to electricity.
Frazil: Ice crystals that form in supercooled water that is too turbulent to
permit the formation of an ice sheet. It is most common in swiftly flowing
streams.
Free atmosphere: That portion of the Earth's atmosphere, upward from about
1,500-3,000 feet above the surface, in which the effect of the Earth's
surface friction on air motion is negligible.
Freeze: A general term referring to the condition that exists when the air
temperature remains below 32 degrees F for a sufficient time to constitute
the characteristic feature of the weather, especially as it relates to its
ability to kill seasonal vegetation.
Freezing fog: Fog, the droplets of which freeze upon contact with exposed
objects like tree branches and form a coating of rime or glaze. Fog
particles usually remain liquid even at air temperatures well below freezing
(32 degrees F), sometimes below 10 degrees.
Freezing level: The lowest altitude in the atmosphere over a given location
at which the air temperatures is 32 degrees F.; the height of the 32-degree
constant-temperature surface.
Freezing rain: Rain that falls in liquid form but freezes upon impact to
form a coating of glaze on the ground and on exposed objects.
Freeze warning: A forecast issued by the National Weather Service when
widespread sub-freezing temperatures are expected to occur within the
normal growing season.
Fremantle Doctor: The local name given to the strong sea breeze that blows
onto the shore areas of southwest Australia, bringing much cooler summer
readings, comparable to, but stronger than, Chicago's lake breeze.
Fresh snow as an insulator: Fresh snow is an excellent insulator. Ten inches
of fresh snow is approximately equal to a six-inch layer of fiberglass
insulation
with an insulation value of R-18.
Freshet: In cold climates, the annual spring rise of streams as a result of
melting snow.
Freshwater fury: An intense low pressure system that crosses the Great
Lakes (especially in November), its strength augmented by the lakes' heat.
Such storms generate high winds and huge lake waves.
Friction layer: The lowest layer of the Earth's atmosphere, extending from
the surface upward to at least 1,500 feet, in which friction with the
surface significantly reduces air motion.
Frigophobia: The irrational or morbid fear of cold or cold things.
Front: The transition zone between two air masses of different density.
Because temperature distribution is the most important regulator of air
density, a front usually separates air masses of different temperatures.
Fronts are due mainly to large-scale movements which bring masses of
air of widely different origin into contact.The length of a front is usually
several hundred miles, but its width can vary from less than one mile up
to 20-40 miles.The term was introduced by Norwegian meteorologists
to denote the line of separation between warm and cold air masses.
When a front does not move, it is called stationary; warm when warmer
air replaces cooler air; cold when cooler air replaces warmer air.
Frontal passage: The movement of a front (the transition zone between
two different air masses) across a location. A frontal passage is usually
accompanied by a characteristic sequence of changes in temperature,
wind direction and speed, humidity, cloudiness and precipitation.
Frontal zone: The boundary or transition zone between two different air
masses. The transition zone may be narrow, a mile or less in width, but it
can be 50 or more miles across. The frontal zone is usually referred to as
simply a "front".
Frontogenesis: (1) The development or marked intensification of a front
(the line of separation between cold and warm masses of air).
Frontogenesis: (2) The initial formation of a front (the transition zone
between two air masses). Usually, differences in temperature and wind
direction mark frontal boundaries; as those differences appear, a front
develops.
Frontolysis: The disappearance or marked weakening of a front (the
separation between cold and warm masses of air). Differences in
temperature and wind direction usually mark frontal boundaries; as those
differences weaken, a front disappears.
Frost: Ice crystals that form on vegetation and objects near the ground
when water vapor in the air sublimes (condenses at sub-freezing
temperatures without passing through the liquid phase) directly onto their
surfaces. Frost is not frozen dew, nor is it considered to be precipitation.
Frost action: The damaging effects of cycles of freezing and thawing of
water contained in natural or man-made materials. The use of deicing salt
greatly exacerbates the destructive effects of the freeze-thaw cycle on
streets.
Frost heave: Ruptured soil, rock or pavement caused by the expansion of
freezing water immediately beneath the surface. It is one of the processes
that initiates the formation of potholes in roads.
Frost hollow: A local bowl-shaped region or depression in the surface into
which cold air drains during clear, calm nights. In such locations in the
upper Midwest, frost can occur even in the summer.
Frostbite: (1) The inflamed, gangrenous effect of excessive exposure to
extreme cold. It usually affects the toes, fingers, ears, and tip of the
nose. Frostbite is rendered more dangerous because there is no sensation
of pain, and the victim may not even know that he has been frostbitten.
Frostbite: (2) Destruction of tissue resulting from freezing, usually
affecting the toes, fingers, ears and tip of the nose. It is especially
dangerous because there is no sensation of pain while it is occurring
and the victim may not even know that he has been frostbitten.
Frostbite: The freezing of skin or flesh. The treatment is slow warming of
the affected area; for example, by skin-to-skin contact or with lukewarm
water. Frostbitten parts are extremely vulnerable to infection, with the
risk of gangrene.
Frostburn: Damage to skin tissue resulting from contact of bare skin with
metal surfaces at below-freezing temperatures.
Fujita, Tetsuya T.: "Mr. Tornado"; Professor Emeritus, University of
Chicago. The world's foremost tornado researcher, Dr. Fujita devised the
F-scale which has become the standard for classifying high wind speeds
based upon the resulting damage.
Fujita (or F) scale: A ranking of the strength of tornado or severe
windstorms based upon damaging winds: F0: winds 40-72 mph; F1:
73-112 mph; F2: 113-157 mph; F3: 158-206 mph; F4: 207-260 mph;
F5: 261-318 mph.
Fujiwhara effect: The tendency of two tropical cyclones (such as hurricanes)
in close proximity to rotate about each other as a result of complex
interactions between their circulations.
Fulgurant: Flashing brightly like lightning.
Fulgurate: To flash or dart like lightning.
Fulgurite: A glassy, root-like hollow tube formed when lightning strikes
sandy soil. The intense heating of the current passing down into the sand
along an irregular path fuses the sand. Concurrently, vaporization of soil
moisture causes the molten material to be expanded into a tube an inch or
more in diameter.
Fulgurous: Suggestive of the flashing of lightning; lightning-like.
Full moon: The moment when the sun is most directly across from the moon,
as viewed from an imaginary position at the center of the Earth. The Earth,
sun and moon are arranged in nearly a straight line.
Funnel: A funnel cloud; a rapidly rotating cone-shaped cloud extending
downward from the base of a convective cloud and made visible by
condensation. Known as a tornado when/if it reaches the ground.
Funnel cloud: A rapidly rotating cone-shaped column of air extending
downward from the base of a convective cloud (usually cumulonimbus,
the thunderhead) and made visible by condensation, but whose circulation
does not make contact with the ground. If it reaches the ground, it is
called a tornado.
Fusion powers the sun: Thermonuclear fusion powers the sun. Every second,
600 million tons of hydrogen fuses into 595 million tons of helium. The five
million tons of lost mass are converted into energy.
Copyright © 2008, WGN-TV
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