Key terms used in turbulence forecasting and aviation weather
Airmen's Meteorological Information. An advisory issued by the National Weather Service for weather conditions that may affect aviation safety, including moderate turbulence, icing, and low visibility. AIRMETs cover less severe conditions than SIGMETs.
Clear-Air Turbulence. Turbulence occurring in cloud-free air, typically near the jet stream at high altitudes. CAT is invisible to radar and cannot be detected visually by pilots, making it one of the most challenging types of turbulence to avoid. It is caused by wind shear associated with jet stream boundaries.
Continental United States. The 48 contiguous states, excluding Alaska and Hawaii. This is the coverage area of NOAA's HRRR weather model and InflightScore's turbulence forecasts.
Turbulence caused by vertical air currents (convection), typically associated with thunderstorms, cumulonimbus clouds, and strong updrafts and downdrafts. Convective turbulence is often visible on weather radar and tends to be more predictable than clear-air turbulence.
Eddy Dissipation Rate. A standardized, aircraft-independent metric for turbulence intensity used by airlines, aviation authorities, and the International Civil Aviation Organization (ICAO). EDR measures the rate at which turbulent kinetic energy dissipates in the atmosphere. Values above 0.2 m²/³/s indicate moderate turbulence.
A diagnostic index for clear-air turbulence developed by Gary Ellrod at NOAA. The Ellrod Turbulence Index (TI-2) combines deformation and convergence of the upper-level wind field to identify regions where jet stream dynamics produce turbulence. It is one of the 11 turbulence diagnostics used by InflightScore.
Altitude expressed in hundreds of feet above the standard pressure datum (1013.25 hPa). For example, FL350 means 35,000 feet. Flight levels are used for altitudes above 18,000 feet in the United States and provide a standardized reference for air traffic control.
High-Resolution Rapid Refresh. A numerical weather prediction model operated by NOAA's National Centers for Environmental Prediction (NCEP). The HRRR runs every hour at 3 km horizontal resolution and forecasts up to 18 hours ahead. It is the highest-resolution real-time weather model available for the contiguous United States and is the primary data source for InflightScore.
A narrow band of strong winds at high altitude, typically between 30,000 and 40,000 feet, flowing from west to east. Wind speeds in the jet stream commonly exceed 100 knots and can reach 200+ knots. The jet stream is a primary source of clear-air turbulence (CAT) due to the strong wind shear at its boundaries.
Turbulence caused by air flowing over mountain ranges, which creates oscillating waves in the atmosphere that can extend to altitudes well above the mountains. Mountain wave turbulence can be severe, particularly in the lee (downwind side) of major mountain ranges like the Rockies, Sierra Nevada, and Appalachians.
Pilot Report. An in-flight weather report filed by a pilot describing conditions encountered during flight, including turbulence intensity, icing, and visibility. PIREPs use a standard intensity scale: Smooth, Light, Moderate, Severe, and Extreme. They are a primary source of real-time turbulence observations.
Significant Meteorological Information. An advisory issued by the National Weather Service for weather phenomena significant to aviation safety, including severe turbulence, severe icing, volcanic ash, and widespread thunderstorms. SIGMETs cover more severe conditions than AIRMETs.
Turbulent Kinetic Energy. A measure of the intensity of chaotic, irregular air motion in the atmosphere. Higher TKE values indicate stronger turbulence. TKE is directly output by the HRRR model and is one of the 11 turbulence diagnostics used by InflightScore.
An abrupt change in wind speed or direction over a short distance, either horizontally or vertically. Vertical wind shear between atmospheric layers at flight altitude is a primary cause of clear-air turbulence. InflightScore calculates wind shear from HRRR wind fields at multiple pressure levels.