The Weather Model of XC Therm


The thermal forecasts displayed on XC Therm originate from the Regtherm model. Regtherm is a convection model tailored to the needs of glider, paraglider, hang glider, and rigid wing pilots.

Regtherm is not an independent weather model but rather takes the forecasts of numeric weather models (currently ICON-EU) as input and extends them with thermal-specific parameters such as climb rates and cloud bases. These parameters are determined by addressing the following effects and methods:

Over two decades, Regtherm has been continuously enhanced by atmospheric physicist and glider pilot Dr. Olivier Liechti in close collaboration with the Deutscher Wetterdienst (DWD). Thanks to the sophisticated and complex computations, Regtherm remains the reference of all thermal forecasts today. Regtherm is used by national weather services and paragliding leagues among others.

More information about the weather model of XC Therm is available in our FAQ.

Segmentation into Homogenous Regions

The borders of the regions are defined by the topography.

Based on the topographic structure (valleys, mountain ranges), Regtherm segments the map into regions where homogenous thermal conditions are expected. Important decision factors are the altitude of the valley floor and the volume of the valleys along the course of a river.

This segmentation into regions provides a comprehensive view and is a clear improvement compared to numerical weather models that segment the map into a fixed grid (e.g. ICON-EU: 7km).

Inclusion of Live Measured Values

The inclusion of live temperature and humidity in the calculation allows Regtherm to predict cloud base and size of cumulus clouds much more accurately for the current day. More details can be found in the FAQ.

Wet ground slows down the development of thermals because a part of the insolation is used for the evaporation of the water. Therefore, Regtherm also considers the rainfall from the past days to weeks.

Wet ground absorbs solar energy for evaporation.

Shadowing due to Clouds

A Halo formed by ice crystals in high altitudes.

All types of clouds reduce the insolation, which has a direct influence on the strength of the thermals.

Regtherm therefore considers the high, medium high, and low layered clouds as well as the developing cumulus clouds in the course of the day for the calculation of the climb rates.

Influence of Vegetation

In Spring, when trees don’t have any leaves yet and the mountain pastures are still brown, the ground is heated up by the insolation faster than in Summer, when the vegetation absorbs part of the solar energy for transpiration (evaporation of water for cooling).

Regtherm considers these seasonal effects caused by the vegetation on the development of thermals.

Brown slopes favor thermal development in Spring.

Horizontal Connection of Regions

Valley winds transport air into higher regions.

Compensation flows such as valley winds that are created by thermal lows have a big influence on the development of thermals, because they transport the humid airmass from lower regions into higher regions. This changes the composition of the air in the course of the day and hence influences the thermals. This often results in a sinking cloud base.

Regtherm therefore considers also the neighboring lower regions for the calculation of forecasts for alpine regions.