ECMWF IFS ENS 0.1°: Wetterensemble

Eastward component of the 100 m wind, describing near-surface flow aloft.

• Comparisons to observations require care because observations represent point measurements rather than grid-box means.
• Combine with the 100 m V component to derive wind speed and direction.

Northward component of the 100 m wind, describing near-surface flow aloft.

• Comparisons to observations require care because observations represent point measurements rather than grid-box means.
• Combine with the 100 m U component to derive wind speed and direction.

Maximum 3‑second wind gust at 10 m height since the last post-processing step.

• Convection effects are included after 2008-10-01; before that, only turbulence is represented.
• Gusts are evaluated each time step and the maximum retained since the last post-processing.

Maximum 3‑second wind gust at 10 m height over the previous 3 hours.

• ECMWF estimates gusts within each time step using surface stress, friction, wind shear, and stability, then selects the maximum over the 3‑hour window.
• Comparisons to observations require care because observations are point measurements.

Eastward (U) component of near-surface wind.

• Combine with the 10 m V component to derive wind speed and direction.
• Observations can diverge due to terrain, vegetation, and local exposure.

Northward (V) component of near-surface wind.

• Combine with the 10 m U component to derive wind speed and direction.
• Observations can diverge due to terrain, vegetation, and local exposure.

Dewpoint temperature describing near-surface moisture conditions. Useful for humidity diagnostics.

• Often combined with temperature and pressure to estimate relative humidity.
• Computed by interpolating between the lowest model level and the surface.

Near-surface air temperature representative of conditions over land, sea, or inland waters. Derived using surface and lowest model level information.

• Units are kelvin (K); to convert to degrees Celsius (deg C), subtract 273.15.
• Mean 2 metre temperature is encoded separately (parameter 228004).

Fraction of incoming shortwave radiation reflected by the snow-covered part of a grid box.

• IFS represents snow as a single layer above the uppermost soil level.
• Albedo varies with snow age and vegetation; typical ranges span 0.52–0.88 for low vegetation and 0.27–0.38 for high vegetation with snow underneath.
• See parameter 228032 for the equivalent value expressed in percent.

Accumulated precipitation from the convection scheme (rain + snow).

• Does not include fog, dew, or precipitation that evaporates before reaching the surface.
• Accumulated over the extraction period; depth in metres of water equivalent.
• See parameter 228143 for the equivalent value expressed in kg m-2.

Horizontal divergence of velocity, indicating spreading or convergence of airflow.

• Positive values indicate divergence (air spreading out); negative values indicate convergence.

Accumulated eastward surface stress from turbulent atmosphere–surface interactions and sub‑5 km orographic form drag.

• Positive values denote stress toward the east; negative values denote westward stress.
• Accumulated over the integration period of the extracted data.

Height derived from geopotential divided by standard gravity (9.80665 m s-2).

• Used on constant pressure levels to diagnose synoptic features (e.g., troughs, ridges, cyclones).
• At the surface, it reflects orography (geopotential height of the surface).
• A geopotential metre is approximately 2% shorter than a geometric metre.

Fraction of a grid box covered by high-level cloud.

• Computed from model levels with pressure < 0.45 of surface pressure (~6 km and above).
• Cloud fractions range from 0 to 1; overlap assumptions are applied across levels.
• See parameter 3075 for the equivalent value in percent.

Fraction of a grid box covered by low-level cloud.

• Computed from model levels with pressure > 0.8 of surface pressure (~2 km and below).
• Cloud fractions range from 0 to 1; overlap assumptions are applied across levels.
• See parameter 3073 for the equivalent value in percent.

Fraction of land within a grid box relative to ocean and inland waters.

• Values range from 0 to 1 and are dimensionless.
• From IFS CY41R1 (May 2015), grid boxes >0.5 may mix land and inland water; <=0.5 are water only.
• Before CY41R1, >0.5 implied land only; <=0.5 implied ocean only (no inland water differentiation).

Fraction of a grid box covered by medium-level cloud.

• Computed from model levels between the low- and high-cloud pressure thresholds.
• Cloud fractions range from 0 to 1; overlap assumptions are applied across levels.
• See parameter 3074 for the equivalent value in percent.

Lowest 2 m temperature observed over the previous 3 hours.

• 2 m temperature is derived by interpolating between the lowest model level and the surface.
• Units are kelvin (K); to convert to degrees Celsius (deg C), subtract 273.15.
• Completed three-hour temperature extrema start at +3h. Anomalous +0h source records are excluded: the audited launch cycles contain 0 K placeholders with contradictory interval metadata. Timeseries can select a prior run's completed interval when eligible under asOf and lead bounds; otherwise it remains missing. Completed intervals and initialization exclusions

Lowest 2 m temperature observed over the previous 6 hours.

• 2 m temperature is derived by interpolating between the lowest model level and the surface.
• Units are kelvin (K); to convert to degrees Celsius (deg C), subtract 273.15.

Atmospheric pressure adjusted to mean sea level, reflecting the weight of the air column.

• Maps of mean sea level pressure highlight cyclones, anticyclones, and wind strength via contour spacing.
• Often expressed in hPa or millibars (1 hPa = 1 mb = 100 Pa).

Convective Available Potential Energy for the most unstable parcel in the layer from the surface to 350 hPa.

• Relates to maximum potential updraft velocity.
• In the lowest 60 hPa, 30‑hPa mixed‑layer parameters are used.

Highest 2 m temperature observed over the previous 3 hours.

• 2 m temperature is derived by interpolating between the lowest model level and the surface.
• Units are kelvin (K); to convert to degrees Celsius (deg C), subtract 273.15.
• Completed three-hour temperature extrema start at +3h. Anomalous +0h source records are excluded: the audited launch cycles contain 0 K placeholders with contradictory interval metadata. Timeseries can select a prior run's completed interval when eligible under asOf and lead bounds; otherwise it remains missing. Completed intervals and initialization exclusions

Highest 2 m temperature observed over the previous 6 hours.

• 2 m temperature is derived by interpolating between the lowest model level and the surface.
• Units are kelvin (K); to convert to degrees Celsius (deg C), subtract 273.15.

Accumulated northward surface stress from turbulent atmosphere–surface interactions and sub‑5 km orographic form drag.

• Positive values denote stress toward the north; negative values denote southward stress.
• Accumulated over the integration period of the extracted data.

Surface precipitation type derived from predicted rain and snow fields plus atmospheric conditions.

• Use alongside precipitation rate to flag events such as freezing rain.
• IFS codes: 0 none, 1 rain, 3 freezing rain, 5 snow, 6 wet snow, 7 rain/snow mix, 8 ice pellets, 12 freezing drizzle.
• IFS does not diagnose WMO codes 2, 4, 9, 10, 11.

Mass of water vapour per kilogram of moist air.

• Moist air includes dry air, water vapour, cloud liquid, cloud ice, rain, and falling snow.

Water vapour pressure as a percentage of saturation.

• For temperatures >0°C, saturation is over water; below -23°C, over ice.
• Between -23°C and 0°C, values are interpolated between ice and water using a quadratic function.

Total surface + subsurface runoff accumulated over the output period, expressed as equivalent water depth.

• Useful as a drought or flood indicator; comparisons to observations require care due to scale and unit differences.
• See parameter 231002 for the equivalent value expressed in kg m-2.

Mass of snow per cubic metre in the model snow layer.

• The IFS represents snow as a layer over the uppermost soil level, with snow covering all or part of a grid box.

Depth of snow expressed as the equivalent depth of water if the snow melted.

• Represents snow over the snow-covered part of the grid box.
• See parameter 228141 for the equivalent value expressed in kg m-2.

Accumulated snowfall at the surface (large-scale + convective).

• Accumulated over the extraction period; depth in metres of water equivalent.
• See parameter 228144 for the equivalent value expressed in kg m-2.

Thickness of sea ice within a grid box.

Temperature of the Earth's surface required to satisfy the surface energy balance.

• Represents the uppermost surface layer with no heat capacity, so it responds instantly to surface flux changes.
• Computed differently over land and sea.
• Units are kelvin (K); to convert to degrees Celsius (deg C), subtract 273.15.
• Mean skin temperature is encoded separately (parameter 235079).

Soil temperature.

• The launch-day source inventory contains soil layers in the 12 UTC run, but not the 06 UTC run. Check run availability when querying these selectors.

Atmospheric pressure at the surface of land, sea, and inland water.

• Often used with temperature to estimate air density.
• Mean sea level pressure is typically preferred for identifying large-scale pressure systems in mountainous regions.
• Often expressed in hPa or millibars (1 hPa = 1 mb = 100 Pa).

Net shortwave radiation at the surface (downward minus reflected).

• Depends on surface albedo and atmospheric absorption/scattering.
• Accumulated over the extraction period; divide by seconds to convert to W m-2.
• ECMWF convention for vertical fluxes is positive downward.

Downward shortwave radiation at the surface (direct + diffuse).

• Approximate model equivalent of pyranometer measurements.
• Accumulated over the extraction period; divide by seconds to convert to W m-2.
• ECMWF convention for vertical fluxes is positive downward.

Net longwave radiation at the surface (downward minus upward).

• Includes atmospheric and cloud emission to the surface and surface emission/reflectance upward.
• Accumulated over the extraction period; divide by seconds to convert to W m-2.
• ECMWF convention for vertical fluxes is positive downward.

Downward longwave radiation at the surface emitted by the atmosphere and clouds.

• Accumulated over the extraction period; divide by seconds to convert to W m-2.
• ECMWF convention for vertical fluxes is positive downward.

Eastward component of surface sea water velocity.

Northward component of surface sea water velocity.

Air temperature throughout the atmosphere.

• Units are kelvin (K); to convert to degrees Celsius (deg C), subtract 273.15.
• Available on multiple vertical levels.

Fraction of a grid box covered by cloud across all model levels.

• Computed from cloud across different heights with overlap assumptions.
• See parameter 228164 for the equivalent value in percent.

Total column cloud ice water (kg/m^2).

Total column cloud liquid water (kg/m^2).

Total column rain water (kg/m^2).

Total column water including vapour, liquid water, cloud ice, rain, and snow.

• Older IFS versions did not include rain and snow in the total.

Total water vapour in a column from the surface to the top of the atmosphere.

• Represents a grid-box mean value.

Accumulated rain + snow at the surface (large-scale + convective).

• Does not include fog, dew, or precipitation that evaporates before reaching the surface.
• Accumulated over the extraction period; depth in metres of water equivalent.
• See parameter 228228 for the equivalent value expressed in kg m-2.

Mean rate of total precipitation (accumulated precipitation divided by the accumulation period).

• Total precipitation includes large-scale + convective rain and snow; excludes fog, dew, and precipitation that evaporates before reaching the surface.
• Units represent depth of water equivalent per second.
• Comparisons to observations require care due to spatial and temporal scale differences.

Net longwave radiation at the top of the atmosphere (negative of OLR).

• Accumulated over the extraction period; divide by seconds to convert to W m-2.
• ECMWF convention for vertical fluxes is positive downward.

Eastward wind component; negative values indicate westward flow.

• Combine with the V component to derive wind speed and direction.

Northward wind component; negative values indicate southward flow.

• Combine with the U component to derive wind speed and direction.

Rotation of horizontal flow about a vertical axis relative to the Earth’s surface.

• Negative/positive values correspond to clockwise/anticlockwise rotation depending on hemisphere; adding the Coriolis parameter gives absolute vorticity.

Volumetric soil moisture content.

• Time-mean volumetric soil moisture is encoded separately (parameter 235077).
• The launch-day source inventory contains soil layers in the 12 UTC run, but not the 06 UTC run. Check run availability when querying these selectors.

Vertical motion in pressure coordinates; negative values indicate upward motion.

• Useful for diagnosing large-scale ascent (negative) and subsidence (positive).

Sea surface height.