How the historical data is processed
Turbli's historical database is built from the forecasts provided by the following agencies:
- NOAA: Graphical Turbulence Guidance forecast
- UK Met Office: Cumulonimbus cloud (thunderstorms) forecast
These agencies update the forecasts every 6 hours, and cover up to 36 hours into the future.
At turbli, the forecasts for 6:00 UTC and 18:00 UTC are stored every day since November 1st, 2021. As the forecast accuracy tends to decrease for further times, the 6 and 18 UTC times are stored when these are closest to the release time of the forecast.
The spatial resolution of the stored forecasts is 0.5 degrees in latitude and longitude, which corresponds to about 25 km (15,500 miles) in distance.
Every point of the stored forecasts is assigned a country or ocean location. Such assignment is based on the boundaries given by the Natural Earth database. No action is taken to correct disputed or conflict zones, and no political views are implied from such decision. Countries smaller than about 80x80 km are removed from the historical data handling since the quality of the weather statistics drawn from these would be low. This includes city states such as Luxembourg or Singapore and small islands such as Malta, Saint Helena, etc.
Overseas territories are added separately when it's considered that they can be under a very different weather system than the rest of the country. Examples are Alaska, Hawaii and Puerto Rico for the US; the French Polynesia and New Caledonia for France; etc. Large countries such as China or Russia are indeed under many different weather patterns as well, but these were not split into different zones.
The altitudes saved in the historical database are 175, 200, 225, 250, 300, 400, 600, 800 and 950 millibars. You can use NOAA's conversion tool to obtain their equivalent in meters or feet. The turbulence rankings and historical data are only computed for the altitudes of 175 to 400 millibars, since these are the most common range of cruising altitudes for commercial aviation. This is about 12,500 to 7,200 m or 41,000 to 23,500 ft. The lower altitudes from 600 to 950 millibars are not yet included in the data presentation.
The turbulence strength is given in units of eddy dissipation rate (edr). This is the standard unit used by NOAA, and it corresponds to the rate at which the energy of turbulent structures is dissipated by viscous forces. High dissipation means that turbulence is also being generated at high rates. The advantage of such unit is that it's aircraft independent, meaning that a measurement of the edr provided by an aircraft would be independent of it's weight or size. These flight measurements can then be used to calibrate the turbulence forecast.
In the turbulence rankings, for each country or ocean the "average maximum" data is computed as the average of each maximum of all saved files. The "average" data is an average of all points.
Cumulonimbus clouds (thunderstorm clouds) are particularly dangerous for flight operations due to their strong upwards and downwards currents. The cumulonimbus cloud forecast from the UK Met Office provides the base elevation, top elevation and extent of the thunderstorm clouds.
The height presented in turbli is between the cloud base to cloud top, not the height at which the cloud is located. The area cover is computed as the percentage of country or ocean area covered by thunderstorm clouds. Areas with thunderstorm clouds smaller than 500 m in height were considered to be in the early developing stage and categorized as no thunderstorm clouds.
In the thunderstorm rankings, no "average cloud height" is presented since regions or entire countries with no clouds would render an erroneous average. Instead, an average thunderstorm "cloud cover" is used.
Please read our Disclaimer regarding the usage of the historical or other data presented in turbli.