Global Data Assimilation System (GDAS)

Best (4-layer) lifted index uses parcels from the lowest four model layers to assess stability at 500 hPa. More negative values indicate greater instability.

• Units: K.
• Often used alongside CAPE and CIN in convective forecasting.

Absolute vorticity combines relative vorticity and planetary vorticity from Earth's rotation. It highlights rotation and dynamical forcing in the flow.

• Units: 1/s.

Convective precipitation accumulation represents precipitation produced by the convection scheme during the output period. It isolates convective rainfall from larger-scale precipitation.

• Units: kg/m².
• Useful for identifying convectively driven rainfall contributions.

Surface albedo is the fraction of incoming shortwave radiation reflected by the surface. Higher albedo means less solar energy absorbed and a cooler surface.

• Units: percent.
• Important for snow and ice feedbacks and surface energy balance.

Accumulated precipitation represents the total water-equivalent amount of rain and snow during the output period. It is a primary field for hydrologic impacts and event totals.

• Units: kg/m^2.
• Use with the model time interval to interpret totals and compare to gauges.

Apparent temperature combines air temperature, humidity, and wind to estimate how hot or cold it feels to humans. It is useful for heat and cold stress assessments.

• Units: K.

Convective Available Potential Energy (CAPE) quantifies buoyant energy available to rising air parcels. Larger values generally imply stronger potential updrafts and greater convective intensity.

• Units: J/kg.
• Often used with CIN and lifting mechanisms to assess thunderstorm potential.

Categorical indicator of freezing rain occurrence at the surface during the output period.

• Units: flag.
• Useful as a mask for icing or glaze hazards.

Categorical indicator of ice pellet (sleet) occurrence at the surface during the output period.

• Units: flag.
• Use with precipitation fields to gauge intensity.

Convective Inhibition (CIN) measures the energy barrier that must be overcome to initiate convection. More negative values indicate a stronger cap that can suppress storms.

• Units: J/kg.
• When CIN is weak and CAPE is high, convection is more likely.

Cloud water mixing ratio is the mass of liquid cloud droplets per mass of air. It describes in‑cloud liquid water content.

• Units: kg/kg.
• Cloud fraction influences surface radiation and temperature.

Plant canopy surface water is liquid water intercepted by vegetation. It represents interception storage and evaporation potential.

• Units: kg/m^2.

Convective probability of precipitation is the chance of convective rainfall during the period. It highlights thunderstorm‑driven precip risk.

• Units: percent.
• Accumulations represent water-equivalent depth over the output interval; rates describe intensity.

Convective precipitation rate is the intensity of precipitation produced by convection. It highlights storm‑driven rainfall rates.

• Units: kg/m²/s.
• Accumulations represent water-equivalent depth over the output interval; rates describe intensity.

Categorical indicator of rain occurrence at the surface during the output period. Useful as a yes/no mask for rain.

• Units: flag.
• Use with accumulation or rate fields for intensity.

Categorical indicator of snow occurrence at the surface during the output period.

• Units: flag.
• Use alongside snowfall/snow-water-equivalent fields.

Cloud water is the total liquid water content (often column‑integrated). It is used to assess cloud water burden.

• Units: kg/m².
• Cloud fraction influences surface radiation and temperature.

Cloud work function is an energy measure used by convection schemes to diagnose convective potential. Larger values generally indicate a more favorable environment for deep convection.

• Units: J/kg.
• Cloud fraction influences surface radiation and temperature.

Downward longwave (thermal) flux represents incoming energy at the surface. It is a key driver of surface heating and cooling.

• Units: W/m^2.
• Shortwave affects surface heating; longwave affects radiative cooling.

Dew point temperature is the temperature at which the air becomes saturated. It is a direct measure of moisture content.

• Units: K.
• When dew point is close to air temperature, fog or low cloud potential increases.

Downward radiative flux represents incoming energy at the surface. It is a key driver of surface heating and cooling.

• Units: W/m^2.
• Shortwave affects surface heating; longwave affects radiative cooling.

Geometric vertical velocity (dz/dt) is the vertical speed of air in height coordinates. Positive values indicate rising motion and negative values sinking motion.

• Units: m/s.

Field capacity is the soil water content after gravitational drainage. It represents the upper limit of plant-available water.

• Units: fraction.

Friction velocity (u*) is a measure of near‑surface shear stress. It is commonly used in turbulence, dust, and air‑sea exchange calculations.

• Units: m/s.

Ground heat flux is the conductive heat exchange between the surface and the subsurface. It is a key term in the surface energy balance.

• Units: W/m^2.

Graupel accumulation represents the water-equivalent amount of graupel in the column. It helps diagnose convective microphysics.

• Units: kg/kg.

Wind gust is the peak short-duration wind speed. It captures brief, hazardous bursts that can exceed sustained winds.

• Units: m/s.

High cloud cover is the fraction of the grid cell covered by clouds in the upper troposphere. It affects longwave radiation and aviation.

• Units: percent.
• Cloud fraction influences surface radiation and temperature.

Geopotential height is the altitude of a pressure surface in the atmosphere. It is the primary field for identifying ridges, troughs, and large‑scale flow patterns.

• Units: gpm.

Haines Index combines stability and moisture to estimate large fire growth potential. Higher values indicate drier, more unstable conditions favorable for fire behavior.

• Units: K.
• Typically used in wildfire forecasting and risk monitoring.

Storm-relative helicity measures the potential for streamwise vorticity to be ingested by a storm updraft. Higher values suggest a greater likelihood of rotating updrafts.

• Units: m^2/s^2.
• Commonly evaluated in the lowest 1 to 3 km layer.

Boundary layer height marks the depth of the turbulent surface-influenced layer. It affects mixing, dispersion, and surface fluxes.

• Units: m.

Icing altitude is the height at which in-flight icing conditions are expected. It is used for aviation routing and hazard awareness.

• Units: m.
• More negative CIN indicates a stronger cap that can suppress convection.

Sea ice cover is the fraction of the grid cell covered by sea ice. It affects surface albedo, heat fluxes, and marine navigation.

• Units: fraction (0-1).

Ice growth rate represents the rate of sea-ice thickness increase. It reflects freezing conditions at the surface and in the upper ocean.

• Units: kg/m^2.

Ice thickness is the physical thickness of sea or lake ice. It is important for marine navigation and heat exchange.

• Units: m.

Ice temperature is the thermal state of sea or lake ice. It affects melting and ice strength.

• Units: K.

Ice water mixing ratio is the mass of ice-phase hydrometeors per mass of air. It indicates ice cloud content.

• Units: kg/kg.

Land cover is a land/sea mask (1=land, 0=water). It is used to separate land and ocean processes.

• Units: flag.

Low cloud cover is the fraction of the grid cell covered by low clouds. It strongly affects visibility, fog potential, and surface temperatures.

• Units: percent.
• Cloud fraction influences surface radiation and temperature.

Lifted Index compares a lifted parcel's temperature to the environment at 500 hPa. More negative values indicate greater instability and thunderstorm potential.

• Units: K.
• Values near zero indicate neutral stability.

Latent heat net flux represents energy exchange due to evaporation/condensation at the surface. It links moisture and energy budgets.

• Units: W/m^2.

Mid-level cloud cover is the fraction of the grid cell covered by clouds in the middle troposphere. It influences both shortwave and longwave radiation.

• Units: percent.
• Cloud fraction influences surface radiation and temperature.

Mean sea level pressure (ETA reduction) is MSLP computed using the ETA model reduction method. It is used for synoptic analysis.

• Units: Pa.

Ozone mixing ratio is the mass of ozone per mass of air. It is used in radiation, chemistry, and upper‑air diagnostics.

• Units: kg/kg.

Potential evaporation rate represents atmospheric demand for evaporation given available energy and wind. It assumes unlimited water supply.

• Units: kg/m²/s.

Pressure of the level from which the parcel was lifted indicates the parcel source level used for stability indices. It helps interpret lifted index and CAPE products.

• Units: Pa.

Potential temperature is the temperature a parcel would have if brought dry‑adiabatically to a reference pressure. It is used for stability.

• Units: K.

Precipitation rate is the total intensity of precipitation over the period. It combines convective and stratiform contributions.

• Units: kg/(m^2 s).
• Accumulations represent water-equivalent depth over the output interval; rates describe intensity.

Pressure is the atmospheric pressure at the specified level. It is a fundamental mass-field variable for dynamics and thermodynamics.

• Units: Pa.

Pressure reduced to mean sea level is MSLP computed from surface pressure and temperature. It is used to locate highs and lows.

• Units: Pa.

Precipitable water is the total column water vapor from the surface to the top of the atmosphere. It is a key moisture indicator.

• Units: kg/m^2.

Composite reflectivity is the maximum reflectivity in the column. It is a standard radar‑style field for identifying convective cores and precipitation intensity.

• Units: dBZ.

Reflectivity is a radar‑style measure of hydrometeor concentration at a given level. Higher values generally correspond to heavier precipitation.

• Units: dBZ.

Relative humidity describes how close the air is to saturation at the specified level. High values favor cloud formation.

• Units: percent.
• Higher values indicate more atmospheric moisture and greater cloud or precip potential.

Rain water mixing ratio is the mass of rainwater per mass of air. It describes rain content within the column.

• Units: kg/kg.
• Accumulations represent water-equivalent depth over the output interval; rates describe intensity.

Surface roughness length is the effective height of surface obstacles that control drag. It strongly influences near-surface wind, turbulence, and exchange fluxes.

• Units: m.

Sensible heat net flux is turbulent heat exchange driven by temperature differences. It affects near‑surface temperature and stability.

• Units: W/m^2.

Snow mixing ratio is the mass of snow particles per mass of air. It describes suspended snow content relevant to microphysics and precipitation.

• Units: kg/kg.
• Accumulations represent water-equivalent depth over the output interval; rates describe intensity.

Snow depth is the physical thickness of the snowpack. It is distinct from snow water equivalent, which measures water content.

• Units: m.

Liquid soil moisture content is the liquid portion of soil water (excluding ice). It directly affects evapotranspiration.

• Units: kg/m^2.
• Soil state affects evapotranspiration and boundary-layer moisture.

Volumetric soil moisture is the fraction of soil volume occupied by water. It is commonly used in hydrology and drought monitoring.

• Units: Fraction.
• Soil state affects evapotranspiration and boundary-layer moisture.

Soil texture class used by the land-surface model. It controls infiltration, drainage, and heat/moisture storage, and strongly affects runoff and evapotranspiration.

• Units: code.

Specific humidity is the mass of water vapor per mass of air at the specified level. It is central to moisture transport.

• Units: kg/kg.
• Higher values indicate more atmospheric moisture and greater cloud or precip potential.

Sunshine duration is the total time with direct sunlight at the surface. It is useful for solar energy and climatological applications.

• Units: seconds.

Total cloud cover is the fraction of the grid cell covered by clouds at any level. It influences radiation, temperature, and visibility.

• Units: percent.
• Cloud fraction influences surface radiation and temperature.

Maximum temperature is the highest temperature reached during the output period. It is commonly used for heat stress and daily extremes.

• Units: K.

Minimum temperature is the lowest temperature reached during the output period. It is commonly used for frost and cold-stress assessment.

• Units: K.

Air temperature is the thermal state of the atmosphere at the specified level. It influences density, stability, and energy exchange.

• Units: K.

Total column ozone is the integrated ozone amount through the atmosphere. It affects UV radiation reaching the surface and atmospheric chemistry.

• Units: Dobson.

Soil temperature describes the thermal state of the soil layer. It affects ground heat flux and freeze/thaw processes.

• Units: K.
• Soil state affects evapotranspiration and boundary-layer moisture.

Zonal gravity wave stress is the east-west component of momentum flux from unresolved gravity waves. It affects large-scale circulation and jet dynamics.

• Units: N/m².

Momentum flux, u‑component is the east‑west surface stress exerted by the atmosphere. It drives boundary-layer dynamics.

• Units: N/m².

U‑component of wind is the east‑west component of the horizontal wind. Combine with v for speed and direction.

• Units: m/s.
• Combine u and v components to compute speed and direction.