USA Weather — Glossary Word Search AS

AAAS

American Association for the Advancement of Science

ACCAS

(usually pronounced ACK-kis) - AltoCumulus CAStellanus; mid-level clouds (bases generally 8 to 15 thousand feet), of which at least a fraction of their upper parts show cumulus-type development. These clouds often are taller than they are wide, giving them a turret-shaped appearance. ACCAS clouds are a sign of instability aloft, and may precede the rapid development of thunderstorms.

Active Surge Region (ASR)

In solar-terrestrial terms, an Active Region that exhibits a group or series of spike-like surges that rise above the limb.

ADAS

Automated Data Acquisition System

Advanced Baseline Imager (ABI)

A moderate resolution imaging system on the GOES and Himawari family of satellites.

Air Mass

A body of air covering a relatively wide area and exhibiting horizontally uniform properties.

Air Mass Thunderstorm

Generally, a thunderstorm not associated with a front or other type of synoptic-scale forcing mechanism. Air mass thunderstorms typically are associated with warm, humid air in the summer months; they develop during the afternoon in response to insolation, and dissipate rather quickly after sunset. They generally are less likely to be severe than other types of thunderstorms, but they still are capable of producing downbursts, brief heavy rain, and (in extreme cases) hail over 3/4 inch in diameter.

Since all thunderstorms are associated with some type of forcing mechanism, synoptic-scale or otherwise, the existence of true air-mass thunderstorms is debatable.

Alaska Current

A North Pacific Ocean current flowing counterclockwise in the Gulf of Alaska. It is the northward flowing (warm) division of the Aleutian Current

ALIASING

The process by which frequencies too high to be analyzed with the given sampling interval appear at a frequency less than the Nyquist frequency.

AMVER/SEAS

A software program created by the National Weather Service intended to efficiently generate AMVER and VOS reports as part of a cooperative effort.

Area Forecast Discussion

This National Weather Service product is intended to provide a well-reasoned discussion of the meteorological thinking which went into the preparation of the Zone Forecast Product. The forecaster will try to focus on the most particular challenges of the forecast. The text will be written in plain language or in proper contractions. At the end of the discussion, there will be a list of all advisories, non-convective watches, and non-convective warnings. The term non-convective refers to weather that is not caused by thunderstorms. An intermediate Area Forecast Discussion will be issued when either significant forecast updates are being made or if interesting weather is expected to occur.

AS

(NOTE: if this appears in an Area Forecast Discussion or other text product in context as the word "as," disregard the technical definition below).

Abbreviation for Altostratus, a cloud of a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus. These clouds are of medium altitude, about 8000 to 20,000 ft (2400-6100 m).

ASAP

1. AHOS SHEF Automatic Processing System

2. As soon as possible (may be used in Area Forecast Discussions)

ASAPTRAN

The software component of ASAP.

ASB

Aviation Support Branch

Ashfall Advisory

An advisory issued for conditions associated with airborne ash plume resulting in ongoing deposition at the surface. Ashfall may originate directly from a volcanic eruption, or indirectly by wind suspending the ash.

ASL

Above Sea Level

ASOS

Automated Surface Observing System. A list of stations currently active and available through the NWS website can be found here.

ASOS IDs

Each Automated Surface Observing System an a four character identifier assigned to it. A list of stations currently active and available through the NWS website can be found here.

ASR-9

Airport Surveillance Radar (FAA)

ASSOCIATED PRINCIPAL USER

A Principal User with dedicated communications to a WSR-88D unit.

Astronomical Dawn

The time at which the sun is 18 degrees below the horizon in the morning. Astronomical dawn is that point in time at which the sun starts lightening the sky. Prior to this time during the morning, the sky is completely dark.

Astronomical Dusk

This is the time at which the sun is 18 degrees below the horizon in the evening. At this time the sun no longer illuminates the sky.

Astronomical Unit

(abbrev. AU)- The mean earth-sun distance, equal to 1.496x10¹³ cm, or 214.94 solar radii.

BANDPASS FILTER

A filter whose frequencies are between given upper and lower cutoff values, while substantially attenuating all frequencies outside these values (this band).

BASE DATA

Those digital fields of reflectivity, mean radial velocity, and spectrum width data in spherical coordinates provided at the finest resolution available from the radar.

Base Flood

In hydrologic terms, the national standard for floodplain management is the base, or one percent chance flood. This flood has at least one chance in 100 of occurring in any given year. It is also called a 100 year flood.

BASE PRODUCTS

Those products that present some representation of the base data. This representation may not necessarily be either in full resolution or depict the full area of coverage. Base products can be used to generate a graphic display or further processing.

Base Reflectivity

Base Reflectivity is the default image. Taken from the lowest (½° elevation) slice, it is the primary image used to "see what's out there". There are two versions of Base Reflectivity image; the short range version which extends out to 124 nautical miles (143 statute miles/230 kilometers) and the long range version which extends out to 248 nautical miles (285 statute miles/460 kilometers). This image is available upon completion of the ½° elevation scan during each volume scan

Base Station

In hydrologic terms, a computer which accepts radio signals from ALERT gaging sites, decodes the data, places the data in a database, and makes the data available to other users.

Base Width

In hydrologic terms, the time duration of a unit hydrograph.

Baseflow

In hydrologic terms, streamflow which results from precipitation that infiltrates into the soil and eventually moves through the soil to the stream channel. This is also referred to as ground water flow, or dry-weather flow.

Basin

An area having a common outlet for its surface runoff. Also called a "Drainage Basin."

Basin Boundary

The topographic dividing line around the perimeter of a basin, beyond which overland flow (i.e.; runoff) drains away into another basin.

Basin Lag

In hydrologic terms, the time it takes from the centroid of rainfall for the hydrograph to peak.

Basin Recharge

In hydrologic terms, rainfall that adds to the residual moisture of the basin in order to help recharge the water deficit. i.e; water absorbed into the soil that does not take the form of direct runoff.

BIAS

A systematic difference between an estimate of and the true value of a parameter.

Brash Ice

In hydrologic terms, accumulation of floating ice made up of fragments not more than 2 meters across; the wreckage of other forms of ice.

CADAS

Centralized Automated Data Acquisition System - a system of two minicomputers in NWSH.

Central Meridian Passage (CMP)

In solar-terrestrial terms, the passage of an Active Region or other feature across the longitude meridian that passes through the apparent center of the solar disk.

Class I Areas

Geographic areas designated by the Clean Air Act where only a small amount or increment of air quality deterioration is permissible.

Closed Basin

A basin draining to some depression or pond within its area, from which water is lost only by evaporation or percolation. A basin without a surface outlet for precipitation falling precipitation.

Closed Basin Lake Flooding

Flooding that occurs on lakes with either no outlet or a relatively small one. Seasonal increases in rainfall cause the lake level to rise faster than it can drain. The water may stay at flood stage for weeks, months, or years.

Coastal Flooding

Flooding which occurs when water is driven onto land from an adjacent body of water. This generally occurs when there are significant storms, such as tropical and extratropical cyclones.

Coastal Waters

Includes the area from a line approximating the mean high water along the mainland or island as far out as 100 nautical miles including the bays, harbors and sounds.

Coastal Waters Forecast (CWF)

The marine forecast for areas, including bays, harbors, and sounds, from a line approximating the mean high water mark (average height of high water over a 19-year period) along the mainland or near shore islands extending out to as much as 100 NM.

Coastal/Lakeshore Flood Advisory

Minor flooding is possible (i.e., over and above normal high tide levels. Coastal/Lakeshore Flood Advisories are issued using the Coastal/Lakeshore Hazard Message (CFW) product.

Coastal/Lakeshore Flood Warning

Flooding that will pose a serious threat to life and property is occurring, imminent or highly likely. Coastal/Lakeshore Flood Warnings are issued using the Coastal/Lakeshore Hazard Message (CFW) product.

Coastal/Lakeshore Flood Watch

Flooding with significant impacts is possible. Coastal/Lakeshore Flood Watches are issued using the Coastal/Lakeshore Hazard Message (CFW) product.

Coastal/Lakeshore Flooding

(i) (Oceanic) Coastal Flooding is the inundation of land areas caused by sea waters over and above normal tidal action. This flooding may impact the immediate oceanfront, gulfs, bays, back bays, sounds, and tidal portions of river mouths and inland tidal waterways. (ii) Lakeshore Flooding is the inundation of land areas adjacent to one of the Great Lakes caused by lake water exceeding normal levels. Lakeshore flooding impacts the immediate lakefront, bays, and the interfaces of lakes and connecting waterways, such as rivers.

Combined Seas

Generally referred to as SEAS. Used to describe the combination or interaction of wind waves and swells in which the separate components are not distinguished. This includes the case when swell is negligible or is not considered in describing sea state. Specifically, Seas² = S²+W² where S is the height of all swell components and W is the height of the wind wave components. When used, SEAS should be considered as being the same as the significant wave height.

Continental Air Mass

A dry air mass originating over a large land area. Contrast with tropical air mass.

County Warning and Forecast Area

The group of counties for which a National Weather Service Forecast Office is responsible for issuing warnings and weather forecasts.

Detention Basins

Structures built upstream from populated areas to prevent runoff and/or debris flows from causing property damage and loss of life. They are normally dry, but are designed to attenuate storm flows or detain mud/debris during and immediately after a runoff event. They have no spillway gates or valves and do not store water on a long-term basis. Typical detention times for storm flows are on the order of 24 to 72 hours, but may be as long as 5 to 10 days. Basins designed for detention of mud and rock debris are periodically excavated to maintain their storage capacity.

Downwash

A deflection of air downward relative to an object that causes the deflection.

Drainage Basin

In hydrologic terms, a part of the surface of the earth that is occupied by a drainage system, which consists of a surface stream or a body of impounded surface water together with all tributary surface streams and bodies of impounded surface water.

Drought Assessments

At the end of each month, CPC issues a long-term seasonal drought assessment. On Thursdays of each week, the CPC together with NOAA National Climatic Data Center, the United States Department of Agriculture, and the National Drought Mitigation Center in Lincoln, Nebraska, issues a weekly drought assessment called the United States Drought Monitor. These assessments review national drought conditions and indicate potential impacts for various economic sectors, such as agriculture and forestry.

Easterlies

Any winds with components from the east.

Easterly Wave

A low level disturbance of tropical origins. Easterly waves can develop into tropical cyclones. However, tropical cyclone development is not required in order for these systems to produce significant amounts of rainfall. The easterly waves are primarily a summer phenomenon.

Ensemble Forecast

Multiple predictions from an ensemble of slightly different initial conditions and/or various versions of models. The objectives are to improve the accuracy of the forecast through averaging the various forecasts, which eliminates non-predictable components, and to provide reliable information on forecast uncertainties from the diversity amongst ensemble members. Forecasters use this tool to measure the likelihood of a forecast.

Ensemble Hydrologic Forecasting

In hydrologic terms, a process whereby a continuous hydrologic model is successively executed several times for the same forecast period by use of varied data input scenarios, or a perturbation of a key variable state for each model run. A common method employed to obtain a varied data input scenario is to use the historical meteorological record, with the assumption that several years of observed data covering the time period beginning on the current date and extending through the forecast period comprises a reasonable estimate of the possible range of future conditions.

Extended Forecast Discussion

This discussion is issued once a day around 2 PM EST (3 PM EDT) and is primarily intended to provide insight into guidance forecasts for the 3- to 5-day forecast period. The geographic focus of this discussion is on the United States (including Alaska and Hawaii). Although portions of this narrative will parallel the Hemispheric Map Discussion, a much greater effort is made to routinely relate the model forecasts and necessary modifications to weather forecasts, mainly in terms of temperature and precipitation.

FASTST

Fastest

Flash

A sudden, brief illumination of a conductive channel associated with lightning, which may contain multiple strokes with their associated stepped leaders, dart leaders and return strokes.

Flash Flood

A rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level, beginning within six hours of the causative event (e.g., intense rainfall, dam failure, ice jam). However, the actual time threshold may vary in different parts of the country. Ongoing flooding can intensify to flash flooding in cases where intense rainfall results in a rapid surge of rising flood waters.

Flash Flood Guidance

(FFG) Forecast guidance produced by the River Forecast Centers, often model output, specific to the potential for flash flooding (e.g., how much rainfall over a given area will be required to produce flash flooding).

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 Table

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

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.

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.

Gas Laws

The thermodynamic laws pertaining to perfect gases, including Boyle's law, Charles' law, Dalton's law and the equation of state.

Global Ensemble Forecast System (GEFS)

A weather forecast model made up of 21 separate forecasts, or ensemble members. The National Centers for Environmental Prediction (NCEP) started the GEFS to address the nature of uncertainty in weather observations, which are used to initialize weather forecast models.

Global Forecast System

(GFS)- One of the operational forecast models run at NCEP. The GFS is run four times daily, with forecast output out to 384 hours.

Great Lakes Marine Forecast (MAFOR)

A National Weather Service coded summary appended to each of the Great Lakes Open Lakes forecasts.

Great Lakes Weather Broadcast

(LAWEB) - A National Weather Service product containing an observation summary prepared to provide Great Lakes mariners with a listing of weather observations along or on the Lakes.

Greenhouse Gases

The gases that absorb terrestrial radiation and contribute to the greenhouse effect; the main greenhouse gasses are water vapor, methane, carbon dioxide, and ozone.

Growing Season

the period of time between the last killing frost of spring and the first killing frost of autumn.

Hazardous Seas Warning

A warning for wave heights and/or wave steepness values meeting or exceeding locally defined warning criteria.

Hazardous Seas Watch

A watch for an increased risk of a hazardous seas warning event to meet Hazardous Seas Warning criteria but its occurrence, location, and/or timing is still uncertain.

Hazards Assessment

CPC's Hazards Assessment provides emergency managers, planners, forecasters and the public advance notice of potential hazards related to climate, weather and hydrological events.

Headwater Basin

In hydrologic terms, a basin at the headwaters of a river. All discharge of the river at this point is developed within the basin.

Hectopascal

A unit of pressure equal to a millibar (1 hPa = 1 mb). Abbreviated hPa.

High Resolution Ensemble Forecast (HREF)

An ensemble of products from several different models running at ~3 km horizontal grid spacing.

High Seas Forecast

(HSF) - Marine forecasts for the major oceans of the world. In this context, major gulfs or seas (e.g., the Gulf of Mexico or the Bering Sea) are included within these forecast areas. Areas of responsibility for the U.S. are determined by international agreements under the auspices of the World Meteorological Organization (WMO).

Hurricane Season

The part of the year having a relatively high incidence of tropical cyclones. In the Atlantic, Caribbean, and Gulf of Mexico, and central North Pacific, the hurricane season is the period from June through November; in the eastern Pacific, May 15 through November 30. Tropical cyclones can occur year-round in any basin.

Hydrologic Ensemble Forecast System (HEFS)

A probabilistic forecast tool with the goals to provide hydrologic forecasts including an analysis of �??probable outcomes�?� and to minimize biases in the atmospheric models and in the hydrologic models.

Ideal Gas Laws

The thermodynamic laws applying to perfect gases.

Interbasin Transfer

In hydrologic terms, the physical transfer of water from one watershed to another.

Intraseasonal Oscillation

Oscillation with variability on a timescale less than a season. One example is the Madden-Julian Oscillation.

ITWAS

Integrated Terminal Weather System

Kilopascal

The internationally recognized unit used by the Atmospheric Environment Service for measuring atmospheric pressure. Abbreviated kPa.

Last Update

The time and date in which the forecast was issued or updated. The forecast may be updated at any time as weather conditions warrant.

Maritime Air Mass

An air mass influenced by the sea. It is a secondary characteristic of an air mass classification, signified by the small "m" before the primary characteristic, which is based on source region. For example, mP is an air mass that is maritime polar in nature. Also known as a marine air mass.

Maritime Polar Air Mass

An air mass characterized by cold, moist air. Abbreviated mP.

Maritime Tropical Air Mass

An air mass characterized by warm, moist air. Abbreviated mT.

Massif

A compact portion of a mountain range, containing one or more summits.

Measured Ceiling

A ceiling classification applied when the ceiling value has been determined by an instrument, such as a ceilometer or ceiling light, or by the known heights of unobscured portions of objects, other than natural landmarks, near the runway. See variable ceiling.

Medium Range Forecast (MRF)

A configuration of the National Water Model (NWM) that runs every 6 hours and produces 3-hourly deterministic forecasts of streamflow and hydrologic states for the contiguous United States (ConUS). This configuration is an ensemble forecast with 7 members; member 1 extends out to 10 days, while members 2-7 extend out to 8.5 days. Meteorological forcing data are drawn from the GFS.

Meteorological Model Ensemble River Forecast (MMEFS)

An automated short-term hydrologic ensemble forecast system which utilizes temperature and precipitation output from the National Centers for Environmental Prediction (NCEP) GEFS and NAEFS meteorological models as inputs to River Forecast Center hydrologic models.

Mid-Latitude Areas

Areas between 30o and 60o north and south of the Equator.

Mount Wilson Magnetic Classifications

In solar-terrestrial terms, a classification system for sunspots:

• Alpha: Denotes a unipolar sunspot group.
• Beta: A sunspot group having both positive and negative magnetic polarities, with a simple and distinct division between the polarities.
• Beta-Gamma: A sunspot group that is bipolar but in which no continuous line can be drawn separating spots of opposite polarities.
• Delta: A complex magnetic configuration of a solar sunspot group consisting of opposite polarity umbrae within the same penumbra.
• Gamma: A complex active region in which the positive and negative polarities are so irregularly distributed as to prevent classification as a bipolar group.

National Digital Forecast Database

(NDFD)- The National Weather Service's NDFD provides access to gridded forecasts of sensible weather elements (e.g., wind, wave height) through the National Digital Forecast Database (NDFD). NDFD contains a seamless mosaic of digital forecasts from NWS field offices working in collaboration with the National Centers for Environmental Prediction (NCEP). The database is made available to all customers and partners from the public, private and academic sectors. Those customers and partners may use this data to create a wide range of text, graphic, gridded and image products of their own.

National Water Model Medium-Range Forecast (NWM MRF)

A 10-day streamflow forecast for the over 3.6 million waterway miles across the Nation, forced by the GFS and updated every 6 hours.

National Water Model Short-Range Forecast (NWM SRF)

An 18-hour streamflow forecast for the over 3.4 million waterway miles across the Nation, forced by the HRRR and updated hourly.

NAVTEX Forecast

(NAV) - A National Weather Service marine forecast combining various Coastal Waters and Offshore forecasts, optimized to accommodate transmission via NAVTEX.

Nearshore Forecast

(NSH) - National Weather Service seasonal marine forecasts for an areas of the Great Lakes extending from a line approximating mean low water datum along the coast or an island, including bays, harbors, and sounds, out to 5 nm. These forecasts are normally issued from Daylight Savings Time ~April 7 through December 31, though the dates may be shortened or extended based on local/regional requirements.

North American Ensemble Forecast System (NAEFS)

An atmospheric ensemble of 20 members each from the NCEP GEFS and CMC EPS ensemble systems.

North American Mesoscale Forecast System (NAM)

One of the major weather models run by the National Centers for Environmental Prediction (NCEP) for producing weather forecasts.

Nor'easter

A strong low pressure system that affects the Mid Atlantic and New England States. It can form over land or over the coastal waters. These winter weather events are notorious for producing heavy snow, rain, and tremendous waves that crash onto Atlantic beaches, often causing beach erosion and structural damage. Wind gusts associated with these storms can exceed hurricane force in intensity. A nor'easter gets its name from the continuously strong northeasterly winds blowing in from the ocean ahead of the storm and over the coastal areas.

Nowcast

A short-term weather forecast, generally out to six hours or less. This is also called a Short Term Forecast.

Numerical Forecasting

A computer forecast or prediction based on equations governing the motions and the forces affecting motion of fluids. The equations are based, or initialized, on specified weather or climate conditions at a certain place and time.

Offshore Waters Forecast

(OFF) - A National Weather Service marine forecast product for that portion of the oceans, gulfs, and seas beyond the coastal waters extending to a specified distance from the coastline, to a specified depth contour, or covering an area defined by specific latitude and longitude points.

Open Lakes Forecast

(GLF) - A National Weather Service marine forecast product for the U.S. waters within a Great Lake not including the waters covered by an existing Nearshore Waters Forecast (NSH). When the seasonal Nearshore forecast is not issued, the Open Lake forecast includes a forecast of nearshore waters.

Overcast

(Abbrev. OVC)- An official sky cover classification for aviation weather observations, when the sky is completely covered by an obscuring phenomenon. This is applied only when obscuring phenomenon aloft are present--that is, not when obscuring phenomenon are surface-based, such as fog.

Pascal

The unit of pressure produced when one newton acts on one square meter (1 N/m²). It is abbreviated Pa.

Persistence Forecast

A forecast that the current weather condition will persist and that future weather will be the same as the present (e.g., if it is raining today, a forecast predicting rain tonight).

Plasma

Any ionized gas; that is, any gas containing ions and electrons.

Probability Forecast

A forecast of the probability that one or more of a mutually exclusive set of weather conditions will occur.

Quantitative Precipitation Forecast

A spatial and temporal precipitation forecast that will predict the potential amount of future precipitation for a specified region, or area.

Quasi-stationary

(abbrev. QSTNRY)- Describes a low or high pressure area or a front that is nearly stationary.

Quasi-stationary Front

A front which is nearly stationary or moves very little since the last synoptic position. Also known as a stationary front.

Rain-free Base

A dark, horizontal cloud base with no visible precipitation beneath it. It typically marks the location of the thunderstorm updraft. Tornadoes may develop from wall clouds attached to the rain-free base, or from the rain-free base itself - especially when the rain-free base is on the south or southwest side of the main precipitation area. Note that the rain-free base may not actually be rain free; hail or large rain drops may be falling. For this reason, updraft base is more accurate.

Right Ascension

The celestial longitude of the sun. This value is 0 at the vernal equinox, 90 at the summer solstice, 180 at the autumnal equinox and 270 at the winter solstice.

River Basin

In hydrologic terms, drainage area of a river and its tributaries.

River Forecast

An internal product issued by RFCs to other NWS offices. An RVF contains stage and/ or flow forecasts for specific locations based on existing, and forecasted hydrometeorologic conditions. The contents of these products are used by the HSA office to prepare Flood Warnings (FLW), Flood Statements (FLS), River Statements (RVS), as well as other products available to the public.

River Forecast Center

Centers that serve groups of Weather Service Forecast offices and Weather Forecast offices, in providing hydrologic guidance and is the first echelon office for the preparation of river and flood forecasts and warnings.

Rough Seas

Sea conditions associated with regionally defined wind thresholds over bays, inlets, harbors, inland waters, and estuaries where larger waves are forming with whitecaps and spray everywhere.

Sastrugi

Ridges of snow formed on a snow field by the action of the wind.

Seas

The combination of both wind waves and swell. Used to describe the combination or interaction of wind waves and swell in which the separate components are not distinguished. This includes the case when swell is negligible or is not considered in describing sea state. Specifically, Seas² = S²+W² where S is the height of the swell and W is the height of the wind wave. When used, Seas should be considered as being the same as the Significant Wave Height

Short Range Forecast (SRF)

A configuration of the National Water Model (NWM) that runs hourly and produces hourly deterministic forecasts of streamflow and hydrologic states out to 18 hours for the contiguous United States (ConUS), and out 48 hours for Hawaii and Puerto Rico/U.S. Virgin Islands. For ConUS, meteorological forcing data are drawn from the HRRR and RAP. For Hawaii and Puerto Rico/U.S. Virgin Islands, meteorological forcing data are drawn from the NAM-Nest with HIRESW WRF-ARW.

Short Term Forecast

A product used to convey information regarding weather or hydrologic events in the next few hours.

SHRAS

showers

Snow Data Assimilation System (SNODAS)

A physically based, mass conserving snow water equivalent (SWE) model.

State Forecast Product

This National Weather Service product is intended to give a good general picture of what weather may be expected in the state during the next 5 days. The first 2 days of the forecast is much more specific than the last 3 days. In comparison with the Zone Forecast Product, this product will be much more general.

Stilling basin

In hydrologic terms, a basin constructed to dissipate the energy of fast-flowing water (e.g., from a spillway or bottom outlet), and to protect the streambed from erosion.

Sunspot Group Classification

• A: A small single unipolar sunspot or very small group of spots without penumbra.
• B: Bipolar sunspot group with no penumbra.
• C: An elongated bipolar sunspot group. One sunspot must have penumbra.
• D: An elongated bipolar sunspot group with penumbra on both ends of the group.
• E: An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 10 deg. but not 15 deg.
• F: An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 15 deg.
• H: A unipolar sunspot group with penumbra.

Surf Zone Forecast

(SRF) - A National Weather Service routine or event driven forecast product geared toward non-boating marine users issued for an area extending from the area of water between the high tide level on the beach and the seaward side of the breaking waves.

Surface-based Convection

Convection occurring within a surface-based layer, i.e., a layer in which the lowest portion is based at or very near the earth's surface. Compare with elevated convection.

Terminal Aerodrome Forecast

This NWS aviation product is a concise statement of the expected meteorological conditions at an airport during a specified period (usually 24 hours). Each country is allowed to make modifications or exceptions to the code for use in each particular country. TAFs use the same weather code found in METAR weather reports.

Texas Hooker

Same as Panhandle Hook - low pressure systems that originate in the panhandle region of Texas and Oklahoma which initially move east and then "hook" or recurve more northeast toward the upper Midwest or Great Lakes region. In winter, these systems usually deposit heavy snows north of their surface track. Thunderstorms may be found south of the track.

Tropical Analysis and Forecast Branch

One of three branches of the Tropical Prediction Center (TPC). It provides year-round products involving marine forecasting, aviation forecasts and warnings (SIGMETs), and surface analyses. The unit also provides satellite interpretation and satellite rainfall estimates for the international community. In addition, TAFB provides support to NHC through manpower and tropical cyclone intensity estimates from the Dvorak technique.

Typhoon Season

The part of the year having a relatively high incidence of tropical cyclones. In the western North Pacific, the typhoon season is from July 1 to December 15. Tropical cyclones can occur year-round in any basin.

Urban Flash Flood Guidance

A specific type of flash flood guidance which estimates the average amount of rain needed over an urban area during a specified period of time to initiate flooding on small, ungaged streams in the urban area.

Volcanic Ash

Fine particles of mineral matter from a volcanic eruption which can be dispersed long distances by winds aloft. The chemical composition and abrasiveness of the particles can seriously affect aircraft and also machinery on the ground. If it is blown into the stratosphere and it is thick enough, it can decrease the global temperature.

Wasatch Wind

A strong easterly wind blowing out of the mouths of the canyons of the Wasatch Mountains onto the plains of Utah. Also called canyon wind.

Weather Forecast Office

(Abbrev. WFO) - this type of National Weather Service office is responsible for issuing advisories, warnings, statements, and short term forecasts for its county warning area

X-Ray Flare Class

In solar-terrestrial terms, rank of a flare based on its X-ray energy output. Flares are classified by the order of magnitude of the peak burst intensity (I) measured at the earth in the 1 to 8 angstrom band as follows:

Class	Intensity (in Watts/m2)
B	I < 10-6
C	10-6 <= I < 10-5
M	10-5 <= I < 10-4
X	I >= 10-4

Zurich Sunspot Classification

In solar-terrestrial terms, a sunspot classification system that has been modified for SESC use.