Weather — page 13 of 38

Weather terms

1201. Ferrel Cell In 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…
1202. Fertilization The union of two gametes from opposite sexes to form a zygote. Typically, each gamete contains a haploid set of chromosomes.
1203. Fertilization, Carbon Dioxide An expression (sometimes reduced to fertilization) used to denote increased plant growth due to a higher carbon dioxide concentration.
1204. Fertilizer Any substance that is added to soil in order to increase its productivity. Fertilizers can be of biological origin (e.g.
1205. Fetch The straight line distance across a body of water subject to wind forces. The distance which wind passes over water.
1206. Few A National Weather Service convective precipitation descriptor for a 10 percent chance of measurable precipitation (0.01 inch).
1207. Few Clouds An official sky cover classification for aviation weather observations, descriptive of a sky cover of 1/8 to 2/8.
1208. FFG Flash Flood Guidance
1209. FG (Also abbrev. F) - Fog - water droplets suspended in the air at the Earth's surface.
1210. Fibril A microscopic to sub-microscopic cellulose thread that is part of the cellulose matrix of plant cell walls.
1211. field Field A region of space at each point of which a given physical or mathematical quantity has some definite value.
1212. Field (Moisture) Capacity The amount of water held in soil against the pull of gravity.
1213. field campaign A 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…
1214. Field Moisture Deficiency The quantity of water, which would be required to restore the soil moisture to field moisture capacity.
1215. Filament A prominence viewed against the solar disk. Also solar irradiance, solar filament.
1216. Filament Channel A broad pattern of fibrils in the chromosphere, marking where a filament may soon form or where a filament recently disappeared.
1217. Fill Dam Any dam constructed of excavated natural materials or of industrial wastes.
1218. Filling The opposite of deepening. A general increase in the central pressure of a low pressure system.
1219. Fire Wind A thermally driven wind blowing radially inward toward a fire, produced by horizontal temperature differences between the heated air above the fire and…
1220. Firebrand Any source of heat, natural or man made, capable of igniting wildland fuels; flaming or glowing fuel particles that can be carried naturally by wind…
1221. 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.
1222. Firn Line The highest level to which the fresh snow on a glacier's surface retreats during the melting season.
1223. First Law of Thermodynamics States that energy cannot be created or destroyed, but only changed from one form to another.
1224. 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.
1225. Flare A 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…
1226. Flaring The burning of waste gases through a flare stack or other device before releasing them to the air.
1227. Flash A sudden, brief illumination of a conductive channel associated with lightning, which may contain multiple strokes with their associated stepped leaders…
1228. Flash Flood A sudden flood event through a valley, canyon, or wash, following a short duration, high-intensity rainfall.
1229. Flash Flood Guidance (FFG) Forecast guidance produced by the River Forecast Centers, often model output, specific to the potential for flash flooding (e.g.
1230. Flash Flood Statement (FFS) In hydrologic terms, a statement by the NWS which provides follow-up information on flash flood watches and warnings.
1231. Flash Flood Table A table of pre-computed forecast crest stage values for small streams for a variety of antecedent moisture conditions and rain amounts.
1232. Flash Flood Warning Flash flooding has been reported or is imminent.
1233. Flash Flood Watch Flash flooding is possible within the designated watch area.
1234. Flash Multiplicity The number of return strokes in a lightning flash.
1235. Flashboards Temporary barriers, consisting of either timber, concrete or steel, anchored to the crest of a spillway as a means of increasing the reservoir storage.
1236. FLG Falling
1237. Float Recording Precipitation gage A rain gage where the rise of a float within the instrument with increasing rainfall is recorded.
1238. Floc Loose, open-structured mass formed in a suspension by the aggregation of minute particles.
1239. Floe An accumulation of frazil flocs (also known as a "pan") or a single piece of broken ice.
1240. Flood A 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…
1241. Flood Categories Terms defined for each forecast point which describe or categorize the severity of flood impacts in the corres­ponding river/stream reach.
1242. Flood Control Storage Storage of water in reservoirs to abate flood damage.
1243. Flood Crest The maximum height of a flood wave as it passes a location.
1244. 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…
1245. Flood Loss Reduction Measures The strategy for reducing flood losses. There are four basic strategies. They are prevention, property protection, emergency services, and structural…
1246. Flood of Record The highest observed river stage or discharge at a given location during the period of record keeping. (Not necessarily the highest known stage.)
1247. Flood Plain A strip of relatively flat and normally dry land alongside a stream, river, or lake that is covered by water during a flood.
1248. 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…
1249. Flood Prevention Measures that are taken in order to keep flood problems from getting worse. Planning, land acquisition, river channel maintenance, wetlands protection…
1250. Flood Problems Problems and damages that occur during a flood as a result of human development and actions.
1251. Flood Profile 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…
1252. Flood Routing A 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…
1253. Flood Stage An established gage height within a given river reach above which a rise in water surface level is defined as a flood.
1254. Flood Statement (FLS) (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.
1255. 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…
1256. Flood Watch Issued to inform the public and cooperating agencies that current and developing hydrometeorological conditions are such that there is a threat of…
1257. Flood Wave A rise in streamflow to a crest and its subsequent recession caused by precipitation, snow melt, dam failure, or reservoir releases.
1258. Flooded Ice Ice which has been flooded by melt water or river water and is heavily loaded by water and wet snow.
1259. Floodproofing The process of protecting a building from flood damage on site. Floodproofing can be divided into wet and dry floodproofing.
1260. Floodwall A long, narrow concrete, or masonry embankment usually built to protect land from flooding.
1261. Floodway (1) A part of the flood plain, otherwise leveed, reserved for emergency diversion of water during floods.
1262. Flow Volume of water that passes a given point within a given period of time. See base flow, discharge, enhancement flow, instream flow requirements…
1263. Flow Duration Curve A cumulative frequency curve that shows the percentage of time that specified discharges are equaled or exceeded.
1264. Flow Separation The process by which a separation eddy forms on the windward or leeward sides of bluff objects or steeply rising hillsides.
1265. 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…
1266. 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.
1267. FLRY Flurry
1268. FLS River Flood Statement
1269. Fluence Time integrated flux
1270. Fluid Liquid.
1271. Fluidized Bed Combustion (FBC) (FBC) A type of furnace or reactor in which fuel particles are combusted while suspended in a stream of hot gas.
1272. Fluorocarbons Carbon-fluorine compounds that often contain other elements such as hydrogen, chlorine, or bromine.
1273. Flurries Snow flurries are an intermittent light snowfall of short duration (generally light snow showers) with no measurable accumulation (trace category).
1274. Flux The amount of energy passing through a unit area (for example, 1m2) per time. On this website, we will be discussing the flux of light energy due to…
1275. FLW Follow (or) Flow- Wind
1276. FM Full Mana
1277. fMin In solar-terrestrial terms, the lowest radiowave frequency that can be reflected from the ionosphere.
1278. FNT Front
1279. FNTGNS Frontogenesis
1280. FNTLYS Frontolysis
1281. 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…
1282. 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.
1283. foEs In solar-terrestrial terms, the maximum ordinary mode radiowave frequency capable of reflec- tion from the sporadic E region of the ionosphere.
1284. foF2 In solar-terrestrial terms, the maximum ordinary mode radiowave frequency capable of reflection from the F2 region of the ionosphere.
1285. Fog Fine particles of liquid suspended in the air, such as of water in a fog chamber used for acclimatizing recent ex vitro transplants. See: mist propagation.
1286. 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.
1287. Forced Channeling Channeling of upper winds along a valley's axis when upper winds are diverted by the underlying topography. Compare pressure-driven channeling.
1288. forcing factors that drive or "force" a system to change. Forcings that affect our climate system include changes in solar radiation and in greenhouse gas…
1289. Forcing Mechanism A process that alters the energy balance of the climate system, i.e. changes the relative balance between incoming solar radiation and outgoing infrared…
1290. Forebay The water behind (upstream) of the dam.
1291. Forecast A statement of prediction.
1292. Forecast Crest The highest elevation of river level, or stage, expected during a specified storm event.
1293. Forecast Guidance Computer-generated forecast materials used to assist the preparation of a forecast, such as numerical forecast models.
1294. 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…
1295. Forecast Periods Official definitions for NWS products: Today...............................Sunrise to sunset This afternoon..................noon till 6 p.m. This evening.
1296. Forecast Point A location that represents an area (reach of a river), where a forecast is made available to the public.
1297. 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.
1298. Foresight A sighting on a point of unknown elevation from an instrument of known elevation.
1299. Forest Terrestrial ecosystem (biome) with enough average annual precipitation (at least 76 centimeters or 30 inches) to support growth of various species of…
1300. Forward Flank Downdraft The main region of downdraft in the forward, or leading, part of a supercell, where most of the heavy precipitation is.