National Blend of Models (NBM) — Alaska core grid

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.

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.

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.

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.

Distance to feature is the horizontal distance to the named hazard or boundary in the source product. It is used to map proximity to key features like fronts or hazards.

• Units: km.

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.

Ellrod index is a diagnostic for clear-air turbulence based on deformation and vertical wind shear. Higher values indicate greater turbulence potential for aviation.

• Units: unitless.

Fractional ice accumulation is an index of ice accretion relative to a reference amount. It is used to describe freezing rain impacts.

• Units: percent.

Fosberg fire weather index combines temperature, humidity, and wind to estimate potential fire spread. Higher values indicate more favorable wildfire conditions.

• Units: unitless.

Freezing spray indicator flags marine conditions favorable for ice accretion on vessels. It depends on wind, air temperature, and wave conditions.

• Units: boolean.

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

• Units: m/s.

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.

Significant wave height represents the average height of the highest third of waves. It is the standard metric for sea state and marine hazards.

• Units: m.

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.

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.

Mixing height is the depth of the well-mixed layer near the surface. It is widely used for dispersion, smoke, and air-quality applications.

• Units: m.

Precipitation duration is the total time with measurable precipitation in the output period. It helps distinguish intermittent from persistent events.

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

Coded surface precipitation type derived from model precipitation and near-surface thermodynamics. It distinguishes rain, snow, freezing rain, mixed types, and related categories.

• Units: coded.
• Interpret together with precipitation rate or accumulation.

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.

Snow-liquid ratio is the ratio of snowfall depth to liquid water equivalent. Higher values indicate lighter, fluffier snow.

• Units: unitless.

Snow level is the approximate altitude where precipitation changes from rain to snow. It is useful for terrain and road-impact forecasting.

• Units: m.

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.

Thunderstorm probability gives the chance of thunderstorms during the valid period. It is used for convective hazard guidance.

• Units: percent.

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.

Tropical wind direction is the direction of the tropical wind vector used in cyclone guidance.

• Units: degrees.

Tropical wind speed is the magnitude of the tropical wind vector. It is often used in cyclone diagnostics.

• Units: m/s.

Thunderstorm indicator flags the presence of thunderstorm conditions in the grid cell. It is used as a categorical hazard field.

• Units: boolean.

Turbulence index is a diagnostic measure of aviation turbulence. Higher values indicate increased turbulence risk along flight routes.

• Units: unitless.

Vertically‑integrated liquid water is the total column liquid water content. It is used as a proxy for precipitation intensity and hail potential.

• Units: kg/m^2.

Horizontal visibility at the surface. Lower values indicate reduced visibility due to fog, precipitation, or aerosols.

• Units: m.

Vertical rate of change is a model diagnostic of vertical motion tendency for the represented variable. It helps identify regions of ascent or subsidence changes.

• Units: 1/s.

Wind direction indicates the direction from which the wind is blowing at the specified level.

• Units: degrees.

Wind speed is the magnitude of the horizontal wind at the specified level. It is used for transport, mixing, and hazards.

• Units: m/s.