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 Term Meaning
ECMWFEuropean Centre for Medium-Range Weather Forecasts
NWPNumerical Weather Prediction. Used in the this guide when statements are applicable to numerical forecast models in general, not only to those in the ECMWF Integrated Forecasting System.
GCMGeneral Circulation Model.
IFSECMWF Integrated Forecasting System
HRESThe High-RESolution model of ECMWF.  A high-resolution (currently 9km),  land-coupled and partially sea-coupled, 3-dimensional general circulation atmospheric model run to day10.  
ENSENSemble model of ECMWF.  A moderate-resolution (currently 18km), land- and sea-coupled, 51-member ensemble, 3-dimensional general circulation atmospheric model run to day15. 
medium-range forecast Comprises HRES and ENS.  Currently day0 to day15.
Extended RangeExtension of ENS.  A lower resolution (currently 36km), land- and sea-coupled, 51-member ensemble, 3-dimensional general circulation atmospheric model run providing an overview of the atmospheric evolution for the 32-day period (day15 to day46) focussing mainly on the week-to-week changes.  It bridges the gap between medium range and seasonal forecasting.

Long-Range, or Seasonal

Long-range Model.  A lower resolution (currently 36km), land- and sea-coupled, 51-member ensemble, 3-dimensional general circulation atmospheric model run providing a broad overview of the atmospheric evolution for the period 2 months to 7 months ahead each calendar month, and to 13 months ahead four times per year.
SEAS, S5Same as Long Range or Seasonal Model.
EUROSIPMulti-model ensemble of international seasonal forecasts.
VAREPS (page14 in link)ECMWF Variable Resolution Ensemble Prediction System.
LegA, LegBObsolete terms for 10day and Extended Range 10-30day ENS forecasts.
ClusteringA method of grouping ENS members according to some measure to highlight the more predictable model forecast height patterns. 
MRMMost representative member.  Used by clustering displays to show the member best describing a cluster. A cluster is represented not by the mean of its members but by its Most Representative Member (MRM)
HTESSELTiled ECMWF Scheme for Surface Exchanges over Land incorporating land surface Hydrology.
TESSELTiled ECMWF Scheme for Surface Exchanges over Land.  Predecessor to HTESSEL. 
FLakeECMWF scheme For surface exchanges over Lake and shallow coastal waters.
LAILeaf Area Index represents the proportion of leaf area at the earth's surface (m2 / m2) and hence determines the degree of evapotranspiration.  It varies climatologically in the IFS model.
SMOS Soil Moisture and Ocean Salinity.  Satellite system measuring surface emission that is strongly related to soil moisture over continental surfaces, salinity and surface state of the oceans, and to the thickness of sea ice.
M-climateModel climate.  A "climate" relevant to the ENS range based on re-forecasts of 20 years data using the same up-to-date model structure and resolution.
ER-M-climateExtended Range Model climate.  A "climate" relevant to the extended range based on re-forecasts of 20 years previous data using the same up-to-date model structure and resolution.
S-M-climateSeasonal Model climate.  A "climate" relevant to the seasonal range based on a re-analyis of 30 years previous data using the same up-to-date model structure and resolution.
ECWAMECMWF Ocean Wave Model evaluates the 2-dimensional surface wave spectrum in both oceanic and coastal waters.
NEMO Nucleus for European Modelling of the Ocean.  A three-dimensional general circulation ocean model. 
LIM2Louvain-la-Neuve sea Ice Model.  Used by NEMO and ECMWF.
LIM3A more advanced Louvain-la-Neuve sea Ice Model not currently used by ECMWF.
4D-VarData assimilation system where the initial condition is adjusted to obtain a best fit of all the observations in the assimilation interval and at the same time tries to stay as close as possible to the forecast first guess for the time of the observation.  It is a method of estimating a set of parameters by optimizing the fit between the solution of the model and the set of observations which the model is meant to predict.
3D-VarData assimilation system where the initial condition is adjusted to obtain a best fit of all the observations in the assimilation interval and weighted according to their distance in time from the nominal data time, and at the same time tries to stay as close as possible to the first guess.  A simpler and less effective technique than 4D-Var but is less expensive in computer time.
EDAEnsemble of Data Assimilation.  Derivation of ensembles of data assimilation for the atmospheric model ensemble. It is used provide a flow dependent background error in 4D-Var, also an estimate of the uncertainty in the analysed atmospheric state.

SV

Singular Vectors.  Vector additions (perturbations) within the IFS system which optimally instigate maximum growth rate of those perturbations.
EDA SVINI
Derivation of Ensembles for Data Assimilation (EDA) for the atmospheric model ensemble using Singular Vector Initialisation.
AMVAtmospheric Motion Vector used in 4D-Var.
LSMLand-sea mask.
ReanalysisReanalysis of archived observations using ECMWF forecast models and data assimilation systems creating global data sets describing the recent history of the atmosphere, land surface, and oceans.  Reanalysis data are used for monitoring climate change, for research and education, for the initialisation of re-forecasts, and for commercial applications.
Re-forecasts

Reforecasts are forecasts run using the same model version as the real-time forecast for a number of past dates and can be used to calibrate real-time ensemble forecasts.  They are used extensively to enable construction of a model climate (e.g. M-climate).  A model climate is not the same a climate from observed data, although for most aspects they are closely correlated.

ERA-InterimA global climate reanalysis from 1979 to date, updated in near-real-time (uses TESSEL scheme).   Re-analyses (and re-forecasts) of past data that are used, in part, to provide a uniform global coverage of "climate" as defined by the model.  It captures also the extremities of observed past conditions, within the constraints of the model resolution (80km).
ERA-Interim offline landA global land surface re-analysis, based on the ERA-Interim atmosphere, but using the H-TESSEL scheme, to improve compatibility with forecasts from more recent ECMWF model versions that also use H-TESSEL.
ERA-Interim WaveA global wave model climate reanalysis from 1979 to date, updated in near-real-time.
ERA5A new ECMWF climate reanalysis to replace ERA-Interim, under construction in 2018 (31km resolution).
ERA-40 A global climate reanalysis from 1957 to 2002.  Re-forecasts of past data to provide a uniform global coverage of a "climate" as defined by the model.  It captures the extremities of observed past conditions relevant to the period of the forecast, within the constraints of the model resolution (125km). 
CERA-20CA global 10-member ensemble of coupled climate reanalyses in the period 1901-2010.  It is based on the CERA assimilation system, which assimilates only surface pressure, marine wind observations, and ocean temperature and salinity profiles.
MACC

Monitoring Atmospheric Composition and Climate.  Operates and improves data-analysis and modelling systems for a range of atmospheric constituents that are important for climate, air quality and surface solar radiation.

SKEBA stochastic backscatter scheme.  Representation of uncertainty in model energy transfer from sub-gridscales to resolved scales.
SPPTA Stochastically Perturbed Parametrization Tendencies scheme.  Representation of uncertainty in model parametrisation schemes.
weightThe weight that may be put on each model output to reflect its likely accuracy.  HRES is most likely to provide more accurate forecasts in the short term, ENS will produce good broad-scale forecasts with less spurious detail at longer lead-times.
NEMOVAR

Multi incremental and multivariate variational data assimilation system for the NEMO ocean model.  Produces ensembles of data assimilation (EDA) for the ocean model ensemble.

ORAS4A global ocean reanalysis from 1957 to date, updated in near-real-time
ORAS5A new ocean reanalysis to replace ORAS4.
ORTA4A global ocean real-time analysis system.
ORTA5A new ocean reanalysis to replace ORTA4.
OSTIAOperational Sea Surface Temperature and Sea Ice Analysis.  High-resolution sea surface temperature data (produced by Met Office), and corresponding sea ice analysis (derived from EUMETSAT Ocean and Sea Ice OSI SAF).
OSI SAFOcean and Sea Ice Satellite Application Facility of  EUMETSAT.   The OSI SAF develops, processes and distributes, in near real-time, products related to key parameters of the ocean-atmosphere interface.  It also offers climatological data records.  The OSI SAF team focuses on scatterometer winds (and soon microwave winds), Sea-Surface Temperature (SST) and sea Ice Surface Temperature (IST), radiative fluxes, and sea ice concentration, edge, type, emissivity, and drift.
CONVModel parameterisation of Convection.
LSWPModel parameterisation of Large Scale Water Processes. 
TGWDModel parameterisation of Turbulence & Gravity Wave Drag.
NOGWModel parameterisation of Non-orographic Gravity Wave Drag.
LDASLand Surface Model.
CINConvective inhibition. The amount of energy that is needed to raise a parcel of air from a given level (such as the surface) up to the level of free convection arising from parcel ascent from that selected level.
LFCLevel of free convection.  The height at which a parcel of air, when lifted, becomes warmer than its surroundings and thus convectively buoyant.
LCLLifted condensation level.  The height at which the relative humidity of a parcel of air parcel will reach 100% with respect to liquid water when it is cooled by dry adiabatic lifting.
SLWSupercooled liquid water.
CAPE

Convective available Potential Energy.  The energy available to a parcel of air rising under free convection.  Indicative of existence of conditional instability and moisture.

CAPE-shear,

CAPE-shear Parameter.  The product of CAPE and vertical wind shear between 925hPa and 500hPa (i.e. the lower troposphere).  Severe storms require CAPE and also lower tropospheric shear.

CAPESHEAR,

CAPES, CSP

Occasionally-used alternative for CAPE-shear found elsewhere in the literature.
DMCDeep moist convection.  Requires three ingredients: conditional instability, moisture and a source of lift.
PDFProbability Density Function.
CDFCumulative Distribution Function.
EFIExtreme Forecast Index.
SOTShift of Tails.
Std

Standard Deviation.

MStdMean Standard Deviation of the spread of the 30 most recent 00UTC or 12UTC model runs
NStdNormalised Standard Deviation.  NStd = Std/Mstd.

MRM

Most Representative Member.  The ENS member most representative of a cluster.
CTRLControl member of the ENS.
EMEnsemble Mean.
RMSRoot Mean Square
PoPProbability of Precipitation
SAFEUMETSAT Satellite Application Facility.

H SAF

Satellite Application Facility on Support to Operational Hydrology and Water Management. Provides precipitation, soil moisture, snow parameters & utilisation of these in hydrological models and NWP
ROM SAF

Radio Occultation Meteorology Satellite Application Facility. Provides near real-time sounding data (temperature, pressure, humidity).

O3M SAFOzone and Atmospheric Chemistry Monitoring Satellite Application Facility. Provides processing of data on ozone, other trace gases, aerosols and ultraviolet radiation.
LSA SAFLand Surface Analysis Satellite Application Facility. Provides data services related to surface radiation, vegetation and wild fire.
OSI SAFOcean and Sea Ice Satellite Application Facility of  EUMETSAT.   The OSI SAF develops, processes and distributes, in near real-time, products related to key parameters of the ocean-atmosphere interface.  It also offers climatological data records.  The OSI SAF team focuses on scatterometer winds (and soon microwave winds), Sea-Surface Temperature (SST) and sea Ice Surface Temperature (IST), radiative fluxes, and sea ice concentration, edge, type, emissivity, and drift.
NWP SAFNumerical Weather Prediction Satellite Application Facility. Development and maintenance of RTTOV, and AAPP.
RTTOV

Radiative Transfer Model.

ATOVS

Advanced TIROS Operational Vertical Sounder.

AVHRR

Advanced Very High Resolution Radiometer.

AAPPATOVS and AVHRR pre-processing package.
SSTSea-surface temperature.
LSWTLake surface water temperature.

SWH, H1/3 or Hs

Significant wave height.  It can be shown to correspond to the average wave height of the one-third highest waves.

SLA

Sea level anomaly.
SSHSea surface height.
MSLMean sea level

TERRA, AQUA

Sun-synchronous orbital satellites with high resolution energy monitoring and imaging systems.
MODISModerate Resolution Imaging Spectroradiometer.
CRYOSAT-2Sea ice mission orbiting satellite.
GPS-ROLim sounding of boundary layer.
IMSNOAA/NESDIS Interactive Multi-sensor Snow and Ice Mapping System.
SMOSSoil Moisture and Ocean Salinity satellite mission.

MJO (page 12 in link)

Madden-Julian Oscillation.

ENSO

El Nino Southern Oscillation.

NAO

North Atlantic Osscilation.
OLROutgoing Long-wave Radiation.
RMSERoot Mean Square Error.
ESLError Saturation Level.
MEMean Error.
MAEMean Absolute Error.
MSEMean Square Error.
ACC

Anomaly Correlation Coefficient

FRFalse Alarm Rate.
FARFalse Alarm Ratio.
HRHit Rate.
weightThe weight that may be put on each model output to reflect its likely accuracy.  HRES is most likely to provide more accurate forecasts in the short term, ENS will produce good broad-scale forecasts with less spurious detail at longer lead-times.
EEExpected Expenses.
BSBrier Score.
BSSBrier Skill Score.
RPS

Rank Probability Score 

CRPSSContinuous Ranked Probability Score
MOSModel Output Statistics
EMOSEnsemble Model Output Statistics
SPPStatistical Post-Processing
ETSEquitable Threat Score
GSSGilbert Skill Score.  Same as Equitable Threat Score (ETS)
ReliabilityThe predicted probability against the frequency with which forecasts verify.
ROCRelative Operating Characteristics

Talagrand diagram

Ranking Histogram
HRES-SAW
HRES-WAM
ENS-WAM
Extended WAM
SEAS-WAM
CAMS
SEEPS
MIR ECMWF Meteorological Interpolation and Regridding package (under test in 2018).
MARS

ECMWF Meteorological Archival and Retrieval System.

FDBECMWF Fields DataBase.  For archival and retrieval.
TCTropical Cyclone
RSMCRegional Specialized Meteorological Center.
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