F1) Fahrenheit- The standard scale used to measure temperature in the United States.
F CoronaIn solar-terrestrial terms, of the white-light corona (that is, the corona seen by the eye at a total solar eclipse), that portion which is caused by…
F RegionIn solar-terrestrial terms, the upper layer of the ionosphere, approximately 120 to 1500 km in altitude.
F ScaleAbbreviation for Fujita Scale, a system of rating the intensity of tornadoes; for detailed information, see the definition for that term.
FaceExposed surface of dam materials (earth, rockfill, or concrete), upstream and downstream. The external surface which limits the structure, see neatlines.
FaculaIn solar-terrestrial terms, a bright region of the photosphere seen in white light, seldom visible except near the solar limb.
Fahrenheit(abbrev. F) The standard scale used to measure temperature in the United States.
FairIt is usually used at night to describe less than 3/8 opaque clouds, no precipitation, no extremes of visibility, temperature or winds.
FallThe amount of slope given to horizontal runs of pipe.
FBO(Great Lakes Freeze-Up/Break-Up Outlook) - A National Weather Service product to keep mariners informed of the projected freeze-up date or break-up date…
FCSTNWSRFS Forecast Program to produce operational forecasts.
Federal Snow SamplerA snow sampler consisting of five or more sections of sampling tubes, one which has a steel cutter on the end.
feedbackthe process by which an initial change brings about additional change that either reinforces or counteracts the initial change.
Feedback MechanismsFactors which increase or amplify (positive feedback) or decrease (negative feedback) the rate of a process.
Feeder BandsLines or bands of low-level clouds that move (feed) into the updraft region of a thunderstorm, usually from the east through south (i.e.
FeedlotConfined outdoor or indoor space used to raise hundreds to thousands of domesticated livestock. See rangeland.
Ferrel CellIn the general circulation of the atmosphere, the name given to the middle latitude cell marked by sinking motion near 30 degrees and rising motion near…
FertilizationThe union of two gametes from opposite sexes to form a zygote. Typically, each gamete contains a haploid set of chromosomes.
Fertilization, Carbon DioxideAn expression (sometimes reduced to fertilization) used to denote increased plant growth due to a higher carbon dioxide concentration.
FertilizerAny substance that is added to soil in order to increase its productivity. Fertilizers can be of biological origin (e.g.
FetchThe straight line distance across a body of water subject to wind forces. The distance which wind passes over water.
FewA National Weather Service convective precipitation descriptor for a 10 percent chance of measurable precipitation (0.01 inch).
Few CloudsAn official sky cover classification for aviation weather observations, descriptive of a sky cover of 1/8 to 2/8.
field campaignA scheduled period of time, or a field campaign, when the frequency of observations is changed to augment routine data acquisition at a site or to satisfy…
Field Moisture DeficiencyThe quantity of water, which would be required to restore the soil moisture to field moisture capacity.
FilamentA prominence viewed against the solar disk. Also solar irradiance, solar filament.
Filament ChannelA broad pattern of fibrils in the chromosphere, marking where a filament may soon form or where a filament recently disappeared.
Fill DamAny dam constructed of excavated natural materials or of industrial wastes.
FillingThe opposite of deepening. A general increase in the central pressure of a low pressure system.
Fire WindA thermally driven wind blowing radially inward toward a fire, produced by horizontal temperature differences between the heated air above the fire and…
FirebrandAny source of heat, natural or man made, capable of igniting wildland fuels; flaming or glowing fuel particles that can be carried naturally by wind…
Firn (Snow)Old snow on top of glaciers, granular and compact and not yet converted into ice. It is a transitional stage between snow and ice. Also called Neve.
Firn LineThe highest level to which the fresh snow on a glacier's surface retreats during the melting season.
First Law of ThermodynamicsStates that energy cannot be created or destroyed, but only changed from one form to another.
Flanking LineA 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.
FlareA rapid release of vast magnetic energy in a sunspot region, causing temperatures to rise tens of millions of degrees in a small area above the solar…
FlaringThe burning of waste gases through a flare stack or other device before releasing them to the air.
FlashA sudden, brief illumination of a conductive channel associated with lightning, which may contain multiple strokes with their associated stepped leaders…
Flash FloodA sudden flood event through a valley, canyon, or wash, following a short duration, high-intensity rainfall.
Flash Flood Guidance(FFG) Forecast guidance produced by the River Forecast Centers, often model output, specific to the potential for flash flooding (e.g.
Flash Flood Statement(FFS) In hydrologic terms, a statement by the NWS which provides follow-up information on flash flood watches and warnings.
Flash Flood TableA table of pre-computed forecast crest stage values for small streams for a variety of antecedent moisture conditions and rain amounts.
FlashboardsTemporary barriers, consisting of either timber, concrete or steel, anchored to the crest of a spillway as a means of increasing the reservoir storage.
FlocLoose, open-structured mass formed in a suspension by the aggregation of minute particles.
FloeAn accumulation of frazil flocs (also known as a "pan") or a single piece of broken ice.
FloodA general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or of two or more properties (at least…
Flood CategoriesTerms defined for each forecast point which describe or categorize the severity of flood impacts in the corresÂponding river/stream reach.
Flood CrestThe maximum height of a flood wave as it passes a location.
Flood Frequency Curve(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…
Flood Loss Reduction MeasuresThe strategy for reducing flood losses. There are four basic strategies. They are prevention, property protection, emergency services, and structural…
Flood of RecordThe highest observed river stage or discharge at a given location during the period of record keeping. (Not necessarily the highest known stage.)
Flood PlainA strip of relatively flat and normally dry land alongside a stream, river, or lake that is covered by water during a flood.
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…
Flood PreventionMeasures that are taken in order to keep flood problems from getting worse. Planning, land acquisition, river channel maintenance, wetlands protection…
Flood ProblemsProblems and damages that occur during a flood as a result of human development and actions.
Flood ProfileA graph of elevation of the water surface of a river in flood, plotted as ordinate, against distance, measured in the downstream direction, plotted as…
Flood RoutingA process of determining progressively over time the amplitude of a flood wave as it moves past a dam or downstream to successive points along a river or…
Flood StageAn established gage height within a given river reach above which a rise in water surface level is defined as a flood.
Flood Statement (FLS)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.
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…
Flood WatchIssued to inform the public and cooperating agencies that current and developing hydrometeorological conditions are such that there is a threat of…
Flood WaveA rise in streamflow to a crest and its subsequent recession caused by precipitation, snow melt, dam failure, or reservoir releases.
Flooded IceIce which has been flooded by melt water or river water and is heavily loaded by water and wet snow.
FloodproofingThe process of protecting a building from flood damage on site. Floodproofing can be divided into wet and dry floodproofing.
FloodwallA long, narrow concrete, or masonry embankment usually built to protect land from flooding.
Floodway(1) A part of the flood plain, otherwise leveed, reserved for emergency diversion of water during floods.
FlowVolume of water that passes a given point within a given period of time. See base flow, discharge, enhancement flow, instream flow requirements…
Flow Duration CurveA cumulative frequency curve that shows the percentage of time that specified discharges are equaled or exceeded.
Flow SeparationThe process by which a separation eddy forms on the windward or leeward sides of bluff objects or steeply rising hillsides.
Flow SplittingThe splitting of a stable airflow around a mountain barrier, with branches going around the left and right edges of the barrier, often at accelerated…
Flowing WellIn hydrologic terms, a well drilled into a confined aquifer with enough hydraulic pressure for the water to flow to the surface without pumping.