In hydrologic terms, a table of pre-computed forecast crest stage values for small streams for a variety of antecedent moisture conditions and rain amounts. Soil moisture conditions are often represented by flash flood guidance values. In lieu of crest stages, categorical representations of flooding, e.g., minor, moderate, etc. may be used on the tables.
Flash Flood Warning
Issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely.
Flash Flood Watch
Issued to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area, but the occurrence is neither certain or imminent.
Flash Multiplicity
The number of return strokes in a lightning flash.
Flashboards
In hydrologic terms, a length of timber, concrete, or steel placed on the crest of a spillway to raise the retention water level but which may be quickly removed in the event of a flood by a tripping device, or by deliberately designed failure of the flashboard or its supports
FLG
Falling
Float Recording Precipitation gage
In hydrologic terms, a rain gage where the rise of a float within the instrument with increasing rainfall is recorded. Some of these gages must be emptied manually, while others employ a self-starting siphon to empty old rainfall amounts.
Floc
A cluster of frazil particles
Floe
In hydrologic terms, an accumulation of frazil flocs (also known as a "pan") or a single piece of broken ice
Flood
Any high flow, overflow, or inundation by water which causes or threatens damage.
Flood Categories
Terms defined for each forecast point which describe or categorize the severity of flood impacts in the corresÂponding river/stream reach. Each flood category is bounded by an upper and lower stage (see Example 1). The severity of flooding at a given stage is not necessarily the same at all locations along a river reach due to varying channel/bank characteristics or presence of levees on portions of the reach. Therefore, the upper and lower stages for a given flood category are usually associated with water levels corresponding to the most significant flood impacts someÂwhere in the reach. The flood categories used in the NWS are: *Minor Flooding* - minimal or no property damage, but possibly some public threat. *Moderate Flooding* - some inundation of structures and roads near stream. Some evacuations of people and/or transfer of property to higher elevations. *Major Flooding* - extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations. *Record Flooding* - flooding which equals or exceeds the highest stage or discharge at a given site during the period of record keeping. Note: all three of the lower flood categories (minor, moderate, major) do not necessarily exist for a given forecast point. For example, at the level where a river reaches flood stage, it may be considered moderate flooding. However, at least one of these three flood categories must start at flood stage.
Flood Control Storage
In hydrologic terms, storage of water in reservoirs to abate flood damage
Flood Crest
Maximum height of a flood wave as it passes a certain location.
Flood Frequency Curve
In hydrologic terms,
(1) A graph showing the number of times per year on the average, plotted as abscissa, that floods of magnitude, indicated by the ordinate, are equaled or exceeded.
(2) A similar graph but with recurrence intervals of floods plotted as abscissa.
Flood Loss Reduction Measures
In hydrologic terms, the strategy for reducing flood losses. There are four basic strategies. They are prevention, property protection, emergency services, and structural projects. Each strategy incorporates different measures that are appropriate for different conditions. In many communities, a different person may be responsible for each strategy.
Flood of Record
In hydrologic terms, the highest observed river stage or discharge at a given location during the period of record keeping. (Not necessarily the highest known stage.)
Flood Plain
In hydrologic terms, the portion of a river valley that has been inundated by the river during historic floods.
Flood Potential Outlook
(ESF on AFOS) (FPO for Acronym): In hydrologic terms, An NWS outlook that is issued to alert the public of potentially heavy rainfall that could send area rivers and streams into flood or aggravate an existing flood.
Flood Prevention
In hydrologic terms, measures that are taken in order to keep flood problems from getting worse. Planning, land acquisition, river channel maintenance, wetlands protection, and other regulations all help modify development on floodplains and watersheds to reduce their susceptibility to flood damage. Preventive measures are usually administered by the building, zoning, planning and/ or code enforcement offices of the local government.
Flood Problems
In hydrologic terms, problems and damages that occur during a flood as a result of human development and actions. Flood problems are a result from:
1) Inappropriate development in the floodplain (e.g., building too low, too close to the channel, or blocking flood flows);
2) Development in the watershed that increases flood flows and creates a larger floodplain, or;
3) A combination of the previous two.
Flood Profile
In hydrologic terms, a graph of elevation of the water surface of a river in flood, plotted as ordinate, against distance, measured in the downstream direction, plotted as abscissa. A flood profile may be drawn to show elevation at a given time, crests during a particular flood, or to show stages of concordant flows
Flood Routing
In hydrologic terms, process of determining progressively the timing, shape, and amplitude of a flood wave as it moves downstream to successive points along the river
Flood Stage
An established gage height for a given location above which a rise in water surface level begins to create a hazard to lives, property, or commerce. The issuance of flood (or in some cases flash flood) warnings is linked to flood stage. Not necessarily the same as bankfull stage.
Flood Statement (FLS)
In hydrologic terms, a statement issued by the NWS to inform the public of flooding along major streams in which there is not a serious threat to life or property. It may also follow a flood warning to give later information.
Flood Warning
(FLW) In hydrologic terms, a release by the NWS to inform the public of flooding along larger streams in which there is a serious threat to life or property. A flood warning will usually contain river stage (level) forecasts.
Flood Watch
Issued to inform the public and cooperating agencies that current and developing hydrometeorological conditions are such that there is a threat of flooding, but the occurrence is neither certain nor imminent.
Flood Wave
In hydrologic terms, a rise in streamflow to a crest and its subsequent recession caused by precipitation, snowmelt, dam failure, or reservoir releases
Flooded Ice
In hydrologic terms, ice which has been flooded by melt water or river water and is heavily loaded by water and wet snow.
Floodproofing
In hydrologic terms, the process of protecting a building from flood damage on site. Floodproofing can be divided into wet and dry floodproofing. In areas subject to slow-moving, shallow flooding, buildings can be elevated, or barriers can be constructed to block the water’s approach to the building. These techniques have the advantage of being less disruptive to the neighborhood. It must be noted that during a flood, a floodproofed building may be isolated and without utilities and therefore unusable, even though it has not been damaged.
Floodwall
In hydrologic terms, a long, narrow concrete, or masonry embankment usually built to protect land from flooding. If built of earth the structure is usually referred to as a levee. Floodwalls and levees confine streamflow within a specified area to prevent flooding. The term "dike" is used to describe an embankment that blocks an area on a reservoir or lake rim that is lower than the top of the dam.
Floodway
In hydrologic terms,
(1) A part of the flood plain, otherwise leveed, reserved for emergency diversion of water during floods. A part of the flood plain which, to facilitate the passage of floodwater, is kept clear of encumbrances.
(2) The channel of a river or stream and those parts of the flood plains adjoining the channel, which are reasonably required to carry and discharge the floodwater or floodflow of any river or stream.
Flow
(abbrev. FLW) Wind. In meteorology, a qualitative reference of an air parcel(s) with respect to its direction of movement, sometimes specified at a certain height or pressure elevation, e.g. westerly flow at 500 mb. In hydrology, the volumetric flow of water past a given point on a stream or river, usually in cubic feet per second (cfs)
Flow Duration Curve
In hydrologic terms, a cumulative frequency curve that shows the percentage of time that specified discharges are equaled or exceeded.
Flow Separation
The process by which a separation eddy forms on the windward or leeward sides of bluff objects or steeply rising hillsides.
Flow Splitting
The splitting of a stable airflow around a mountain barrier, with branches going around the left and right edges of the barrier, often at accelerated speeds.
Flowing Well
In hydrologic terms, a well drilled into a confined aquifer with enough hydraulic pressure for the water to flow to the surface without pumping. Also called an Artesian well.
FLRY
Flurry
FLS
River Flood Statement
Fluence
Time integrated flux
Fluid
Matter which flows; gas or liquid.
Flurries
Snow flurries are an intermittent light snowfall of short duration (generally light snow showers) with no measurable accumulation (trace category).
Flux
The rate of transfer of fluids, particles or energy per unit area across a given surface (amount of flow per unit of time).
FLW
Follow (or) Flow- Wind
FM
From or Fathom
fMin
In solar-terrestrial terms, the lowest radiowave frequency that can be reflected from the ionosphere.
FNT
Front
FNTGNS
Frontogenesis
FNTLYS
Frontolysis
Foehn
A warm, dry wind on the lee side of a mountain range, the warmth and dryness of the air being due to adiabatic compression as the air descends the mountain slopes. In the United States, the term chinook is used for Foehn winds in the Rocky and Sierra mountains.
Foehn Pause
A temporary cessation of the foehn at the ground due to the formation or intrusion of a cold air layer which lifts the foehn off the ground.
foEs
In solar-terrestrial terms, the maximum ordinary mode radiowave frequency capable of reflec- tion from the sporadic E region of the ionosphere.
foF2
In solar-terrestrial terms, the maximum ordinary mode radiowave frequency capable of reflection from the F2 region of the ionosphere.
Fog
(abbrev. F) Fog is water droplets suspended in the air at the Earth's surface. Fog is often hazardous when the visibility is reduced to ¼ mile or less.
Fogbow
A rainbow that has a white band that appears in fog, and is fringed with red on the outside and blue on the inside.
Forced Channeling
Channeling of upper winds along a valley's axis when upper winds are diverted by the underlying topography. Compare pressure-driven channeling.
Forebay
In hydrologic terms, the water behind (upstream) of the dam.
Forecast
A statement of prediction.
Forecast Crest
In hydrologic terms, the highest elevation of river level, or stage, expected during a specified storm event.
Forecast Guidance
Computer-generated forecast materials used to assist the preparation of a forecast, such as numerical forecast models.
Forecast Issuance Stage
The stage which, when reached by a rising stream, represents the level where RFCs need to begin issuing forecasts for a non-routine (flood-only) forecast point. This stage is coordinated between WFO and RFC personnel and is not necessarily the same as action or alert stage. The needs of WFO/RFC partners and other users are considered in determining this stage.
Forecast Periods
Official definitions for NWS products:
Today...............................Sunrise to sunset
This afternoon..................noon till 6 p.m.
This evening.....................6 p.m. till sunset
Tonight.............................sunset till sunrise
Tomorrow.........................sunrise to sunset of the following day
Forecast Point
A location along a river or stream for which hydrologic forecast and warning services are provided by a WFO. The observed/forecast stage or discharge for a given forecast point can be assumed to represent conditions in a given reach (see /reach/).
Forecast valid for
The period of time the forecast is in effect beginning at a given day, date and time, and ending at a given day, date and time.
Foresight
In hydrologic terms, a sighting on a point of unknown elevation from an instrument of known elevation. To determine the elevation of the point in question, the foresight is subtracted from the height of the instrument.
Forward Flank Downdraft
The main region of downdraft in the forward, or leading, part of a supercell, where most of the heavy precipitation is.
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 fog the droplets of which freeze upon contact with exposed objects and form a coating of rime and/or glaze.
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 for 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.
Frostbite
Human tissue damage caused by exposure to intense cold.
Frozen Dew
When liquid dew changes into tiny beads of ice. This occurs when dew forms and temperatures later drop below freezing.
FRST
Frost- 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.
FRZ
Freeze
FRZN
Frozen
FSCBG
A specific aerial spray dispersion model. The acronym comes from the names of the sponsor and developers (Forest Service, Cramer, Barry, Grim).
FT
Feet (or foot)
FTHR
Further
FTPMAIL
An Internet server application which provides access to Internet FTP server files via e-mail. The National Weather Service operates an FTPMAIL server which provides e -mail access to any product available on the tgftp.nws.noaa.gov FTP server including marine text and graphic forecasts. For further information see: http://weather.noaa.gov/pub/fax/ftpmail.txt, or send an e-mail to ftpmail@ftpmail.nws.noaa.gov with the word "help" in the body.
Fugitive Dust
Dust that is not emitted from definable point sources such as industrial smokestacks. Sources include open fields, roadways, storage piles, etc.
Fujita Scale
(or F Scale) - A scale of tornado intensity in which wind speeds are inferred from an analysis of wind damage:
|
Rating |
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, devestating damage |
|
F5 (violent) |
260-318 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.
Fujiwhara Effect
A binary interaction where tropical cyclones within a certain distance (300-750 nm depending on the sizes of the cyclones) of each other begin to rotate about a common midpoint.
Full-Physics Numerical Model
A computer model used to calculate air pollution concentrations. A full-physics numerical model uses a full set of equations describing the thermodynamic and dynamic state of the atmosphere and can be used to simulate atmospheric phenomena.
Fumigation
A pattern of plume dispersion produced when a convective boundary layer grows upward into a plume trapped in a stable layer. The elevated plume is suddenly brought downward to the ground, producing high surface concentrations.
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.
Funnelling
The process whereby wind is forced to flow through a narrow opening between adjacent land areas, resulting in increased wind speed.
FVT
Forecast Verification Tool
FWC
NGM MOS Guidance
FWD
Forward
FZRA
freezing rain
G
Gusts- A rapid fluctuation of wind speed with variations of 10 knots or more between peaks and lulls.
G/KG