Rapid Refresh Forecast System Ensemble (RRFS Ensemble)

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.

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.

Aerosol optical thickness represents the column-integrated attenuation of solar radiation by aerosols. Larger values indicate hazier conditions and reduced surface sunlight.

• Units: dimensionless.
• Useful for visibility, air quality, and solar energy assessments.

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.

Accumulated snow depth is the total depth of snow on the ground over the period. It is a physical depth, not water equivalent.

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

Brightness temperature is the blackbody temperature that would emit the observed radiance in a spectral channel. It is used for satellite and cloud diagnostics.

• 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.

Drag coefficient represents the aerodynamic resistance between the surface and the atmosphere. It controls surface stress and is used in momentum and heat flux calculations.

• Units: dimensionless.

Ceiling height is the altitude of the lowest cloud base that covers a significant portion of the sky. It is a key aviation and surface-visibility metric.

• Units: m.

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.

Cumulative infiltrated soil moisture is the total water that has infiltrated into the soil. It reflects soil intake capacity and wetting history.

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

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.

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.

Clear‑sky downward shortwave flux is broadband solar energy at the surface without cloud effects.

• Units: W m-2.

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

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

Dew point depression is the difference between air temperature and dew point. Small values indicate near‑saturation.

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

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.

East longitude gives the longitude position of the grid point in degrees east. It is a static geographic coordinate field.

• Units: degrees.

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.

Freezing rain accumulation is the water-equivalent amount of freezing rain during the period. It relates directly to ice accretion risk.

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

Freezing rain probability gives the chance of freezing rain during the period. It supports icing risk guidance.

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

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.

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

• Units: flag.
• Use with hail probability or severe indices for risk context.

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.

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 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.

Soil layer thickness specifies the depth of the modeled soil layer. It helps interpret soil moisture and temperature fields.

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

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.

Lightning indicates flash frequency or density, a proxy for convective intensity. Higher values suggest stronger or more frequent thunderstorms.

• Units: flashes/km2/s.

Hourly maximum downward vertical velocity in the lowest 400 hPa highlights the strongest subsidence within the lower troposphere during the hour.

• Units: Pa/s.

Hourly maximum simulated reflectivity at 1 km AGL captures the strongest modeled reflectivity near the surface. It is used to identify peak convective intensity and heavy precipitation cores.

• Units: dBZ.

Maximum relative humidity is the highest RH reached during the period. It can indicate peak cloud or fog potential.

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

Hourly maximum upward vertical velocity in the lowest 400 hPa highlights the strongest updrafts within the lower troposphere during the hour.

• Units: Pa/s.

Maximum u‑component of wind is the strongest east‑west flow during the period. It helps identify peak wind directions.

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

Maximum v‑component of wind is the strongest north‑south flow during the period.

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

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.

Moisture convergence is the horizontal convergence of water vapor transport. Areas of convergence favor rising motion and precipitation development.

• Units: kg/(m^2 s).

Minimum relative humidity is the lowest RH reached during the period. It is used in fire‑weather and drying assessments.

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

Hourly minimum updraft helicity is the lowest helicity value during the hour. It provides a lower bound on rotating updraft potential.

• Units: m2/s2.

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

• Units: Pa.

Moisture availability represents how much moisture is available at the surface for evaporation. It is used in land-surface and fire-weather diagnostics.

• Units: percent.

Maximum snow albedo is the highest reflectivity of the snow surface during the period. Higher values indicate fresher, brighter snow.

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

Hourly maximum updraft helicity (2–5 km AGL) highlights the strongest rotating updrafts during the hour.

• Units: m2/s2.

North latitude gives the latitude position of the grid point in degrees north. It is a static geographic coordinate field.

• Units: degrees.

Potential evaporation is the amount of water that could evaporate if sufficient moisture were available. It reflects atmospheric demand.

• Units: kg/m^2.

Parcel lifted index compares a lifted parcel temperature to the environment at 500 hPa. More negative values indicate greater instability and thunderstorm potential.

• Units: K.
• More negative values indicate greater instability.

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.

Soil porosity is the fraction of soil volume that is pore space. It governs storage and drainage capacity.

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

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.

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 vorticity measures local rotation of the horizontal wind field. Positive values indicate cyclonic rotation and negative values anticyclonic rotation.

• Units: 1/s.

Echo top height is the altitude of the highest reflectivity in the column. It is a proxy for storm depth and convective vigor.

• Units: m.

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.

Relative humidity with respect to precipitable water is a column‑scale moisture indicator based on total water vapor content.

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

Number of soil layers is a static model metadata field describing the soil discretization.

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

Minimum stomatal resistance is a vegetation parameter controlling transpiration efficiency. Lower values allow stronger evapotranspiration under favorable conditions.

• Units: s m-1.

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.

Surface exchange coefficient is the bulk transfer coefficient used to compute turbulent heat and moisture fluxes. It depends on stability and roughness.

• Units: dimensionless.

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

• Units: W/m^2.

Dry soil moisture content represents the soil water deficit or dry portion relative to saturation. It highlights drought stress in the soil column.

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

Reference soil moisture is a model-specific baseline (often near field capacity) used for anomalies and normalization.

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

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.