Frequently Asked Questions - FAQ

No. XC Therm is a so-called Progressive Web App (PWA). This means that XC Therm runs directly in the browser, but it can be saved to your phone's home screen. Like this it will behave like a regular app from the App Store or Google Play.

Yes, the thermal forecasts are available in the archive for subscribers starting from December 6, 2012. The archive will always show the latest forecast for the chosen date.

The archive data for the period 06.12.2012 - 31.12.2023 comes from the old Regtherm regions (Alps and Central Europe). From 01.01.2024 onwards, the archive is available for the new Regtherm regions (all of Europe).

Due to the enormous amount of data, ICON-D2 forecasts from the past are not available.

Yes, the ICON-D2 wind and weather forecasts from XC Therm can be integrated in any website using an iFrame. Detailed instructions are available here (German only).

Due to technical limitations, the thermal forecasts cannot be integrated into other websites.

The philosophy of XC Therm is to provide pilots all necessary tools so they can take their own decisions. For that reason, XC Therm will not issue any wind or Foehn warnings and also no recommendations, in which flight region a pilot should go.

Using the high-resolution thermal, wind and weather forecasts, pilots have all the tools necessary to assess the situation. Based on their individual flight skills, pilots can then decide on their own, which region is the best for them.

There is now also a forum on XC Therm so that feedback on XC Therm can be collected in one central location. This is primarily aimed at glider pilots, but may of course also be used by other pilots.

As this forum is independent of the rest of the website, a separate login is required. To ensure the quality of the forum (spam, bots...) every new forum member must be authorised by an admin.

Link to the forum

A change of subscription can only be performed by us at the moment. Please write an email to so we can perform the change of subscription for you.

Changing to a bigger subscription is possible at any time, changing to a smaller subscription however only at the time of renewal. When upgrading a subscription, the current subscription will be canceled and the unused part of the subscription fees of the old subscription will be subtracted from the amount due for the new subscription and the difference will be charged directly to your registered payment method. The new subscription will then be valid for a full year.

We prefer payments with credit cards because the subscriptions can be activated immediately and will also be booked automatically in our accounting.

Should you not be in possession of a credit card though, we allow prepayment to our bank account. In this case proceed as follows:

1. Register on XC Therm and confirm your email address. But don't select a subscription yet.
2. Send an email to and let us know, what email address you used for the previous step, in which country you live and what subscription you would like.
3. Wait until we send you our bank details.
4. Transfer the exact amount for your requested subscription to our bank account.

After receiving your payment, your subscription will be activated within 24 hours.

To find out whether the regional subscription or the premium subscription is sufficient for you, we recommend that you visit the Demo. Currently, we are showing the new test regions in the demo, so the Europe-wide coverage is not yet visible there.

An overview of the number of regions per country is also provided by the following tables. They refer to the new definitive regions. Note that regions are also counted as part of a country if they are only partially located in this country. Border regions have therefore been counted multiple times in these tables.

You should select all your regions right from the start, as adding regions later on will count towards your limit of 6 allowed changes.

Should you already have misunderstood this and you already used up your allowed changes, send us an email to . We will reset the counter once for you.

The old region selection expires on 31.12.2023, as the new test regions do not match the old regions. At the first login in the new year 2024, you can make a new selection. You can choose from the 654 new test regions.

When switching to the new definitive regions in spring 2024, you will be able to change your selection again. Then you can choose from over 1000 new definitive regions.

These changes do not count towards the 6 allowed changes.

For the archive you don't need the old region selection either. From January 2024, the archive of all regions will be freely accessible to all users.

You can do that in the menu under Subscription -> Manage Subscription.

Yes, we give discounts to groups of at least 10 people. The actual amount of the discount depends on the number of subscriptions bought by the group's members. Please contact us at .

It is however not possible to create a group account for all members. Each member must have its own subscription.

Of course not. It is also not allowed to post forecasts in private of public chat groups without prior permission. Also, it is not allowed to use bots / scripts to download the forecasts systematically.

Just the way you want to be paid when you go to work, we also would like to be paid for our big efforts we put into XC Therm. Our infrastructure is expensive as well as our development is expensive. That's why we need the revenues from the subscriptions.

We count on your fairness.

The Model Operation and the Providers

Until December 2023, XC Therm visualized the Regtherm thermal forecasts produced by the German Weather Service DWD. From January 2024, XC Therm will take over the operation of the Regtherm model in addition to the visualization. Other providers of the Regtherm forecasts such as Alptherm (AustroControl), Toptask, Flugwetter.de will be discontinued after 31.03.2024.

The Regions

First, the regions in the already covered areas were refined to capture the differences in air masses better and enable more detailed flight planning. Second, new regions were defined to cover larger parts of Europe.

From 01.01.2024, 654 new test regions will be calculated and visualized. You can send us feedback on the naming and delimitation of the regions until end of January to optimize the division (more on this below). In spring 2024, we will launch the definitive new regions with further refinements and expanded geographical coverage. Soon, Regtherm thermal forecasts for all of Europe will be available on XC Therm!

You can find more details under the next questions.

The Input Data

For the first time, the regions in Central Europe will retrieve their input data from the ICON-D2 model (instead of ICON-EU) for the first 2 forecast days. The higher resolution of 2.2 km allows the input model ICON-D2 to better represent small-scale atmospheric processes. Using measurement station input data becomes therefore unnecessary and will be omitted. For the forecast days 3-5, as well as for the areas outside the ICON-D2 coverage, ICON-EU input data will be used.

You can find an overview of the news here.

The Model

For over two decades, Regtherm has been the reference for all thermal forecasts thanks to its sophisticated and elaborate calculations. In the future, the Regtherm model it will continue to be developed and improved by atmospheric physicist and glider pilot Dr. Olivier Liechti. While the appearance of the thermal forecasts may change with the new regions, the calculations in the background and thus the quality of thermal forecasts will remain unchanged.

The Visualization

The XC Therm Platform will continue to provide the familiar, clear thermal overviews and detailed forecasts.

The Subscriptions

More regions = higher prices? Not with us. The prices for subscriptions will remain the same. All Unlimited subscribers now have access to regional thermal forecasts for 654 (later over 1000) regions instead of the previous 289.

The 289 old regions were designed for gliders many years ago. They are relatively coarse and cover the Alps and Central Europe.

The 654 new test regions were created in 2023. The regions are more detailed and expand the coverage of the Regtherm model in Spain, Italy, Poland, and Sweden. Together with your feedback, the new test regions help us improve the definitive new regions. More on how to give feedback is found below the next questions.

The 1000+ definitive new regions are currently being created. They close the coverage gaps in Europe and optimize the division with the knowledge of local pilots. The definitive new regions will cover all of Europe.

The old regions were originally designed for gliders and were too large to capture the air mass differences relevant for paragliding. For example, the region Berner Oberland stretched from Rochers-de-Naye at Lake Geneva to Pilatus in Central Switzerland, covering a distance of 120 km. Every pilot knows that thermal conditions and cloud base heights can vary significantly in such a large area.

With the new regions, Regtherm can now capture air mass boundaries between larger valleys in the mountains and provide distinct thermal forecasts. The old region Berner Oberland has been divided into three new regions: Berner Oberland, Berner Alpen, and Urner Alpen. The new regions are as small as necessary to capture characteristic air mass boundaries, and as large as possible for the thermal overview to remain clear and user-friendly.

The subdivision of the map into Regtherm regions is based on topographic characteristics such as the course of mountain ranges, the elevation of valley floors, the volume of valleys, and the average elevation of the terrain.

This topography-based subdivision relies on scientific findings showing that convective mixing of the atmosphere mainly occurs along thermal circulation systems (slope wind, valley wind, alpine pumping). As a result, homogeneous atmospheric conditions are found 1) in valleys and 2) in regions with similar terrain heights.

In addition, the experience of local meteorologists and pilots regarding characteristic and recurring air mass boundaries can be useful to refine regions more accurately. In your local flying region, you undoubtedly know such boundaries where the strength of thermals and the base of cumulus clouds frequently change. For the creation of the 1000+ new definitive regions, we interviewed numerous local pilots throughout Europe.

Also your feedback is valuable if you see potential for improvement in the delineation or naming of a region. If you believe that a region has been delineated inappropriately or if you have a more suitable name, do not hesitate to contact us before 31.01.2024 at . Your input helps us improve the forecast and the platform. It should be noted in advance that we will take every feedback seriously, but may not be able to address every concern and suggestion.

One might think that to get even more precise predictions, very small regions should be defined, down to the smallest valley in the Alps. However, it's not that simple because the input models ICON-EU and ICON-D2 do not have the necessary grid resolution to capture such small-scale differences. If there is no air mass difference in the input data, the Regtherm forecast will hardly be able to depict a difference in thermal strength or cloud base height. Therefore, the regions were refined only to the extent that the input model can still capture the topographic characteristics in its horizontal resolution. The new regions are therefore as small as necessary to capture characteristic air mass boundaries, and as large as possible for the thermal overview to remain clear and user-friendly.

Example:

Ideally, we could define each small valley as a thermal region, making sure the Regtherm model also simulates the micro-meteorological processes taking place.

On the one hand, such a division with very small areas would lead to a loss of overview. Countless detailed forecasts would have to be examined in order to plan a longer XC-flight and one would get lost in the details. On the other hand, a fine-meshed division is useless if the input model does not resolve the topography sufficiently. The ICON-D2 can still "see" most of the valleys through its 2.2 km grid, but these valleys are heavily flattened in the ICON-D2 topography.

Considering the ICON-EU topography, it becomes apparent that the input model has its limits and that therefore only the coarser categorization makes sense. With the new regions, topography is divided into homogeneous regions, with the mountain ranges separating the greater valley wind systems. The ICON-EU input model also "sees" these valleys and can therefore recognize potential air mass differences.

The old regions have definitively been replaced by the new ones. It is therefore no longer possible to obtain thermal forecasts for the old regions. The same applies to the new test regions after the next update in spring 2024.

However, if you have insights into the new region subdivision or the quality of thermal forecasts for the new regions, do not hesitate to contact us at .

Regtherm is not a standalone weather model; instead, it uses forecasts from numerical weather models as input data and calculates thermal-specific parameters such as lift rates and cloud base heights. Until 2023, input data exclusively from the ICON-EU weather model was used. Starting from 2024, the high-resolution ICON-D2 model will also be used alongside ICON-EU.

Firstly, the ICON-D2 model only covers Central Europe. The following illustration shows the regions where ICON-D2 data is available and is used as input data for Regtherm.

Secondly, ICON-D2 forecasts only go as far as 2 days into the future. For forecast days 3-5, ICON-EU model data will be used as input data for all regions. The following table provides an overview of the input data for the Regtherm model.

Additionally, the weather model on which a Regtherm forecast is based is always displayed in the top right corner of the detailed forecast.

In the past, the Regtherm calculation also included current measurement data. With today's high horizontal resolution of the input data, these measurements are already included well enough in the weather models themselves and do not need to be reintegrated in Regtherm. Therefore, the real-time measurement data is no longer used as Regtherm input data.

The following tables provide information about the update times of thermal forecasts. Since the calculation of Regtherm takes a few minutes, the forecasts for following days are updated with a few minutes delay.

For the first two forecast days, the Regtherm model uses the ICON-D2 model as input data for thermal forecasting where available. The thermal forecasts are updated at the following times:

For all areas outside the ICON-D2 coverage and for forecast days 3, 4, and 5 of all areas, the Regtherm model uses the ICON-EU model as input data for the thermal forecasts. The forecasts are updated at the following times:

Until December 2023, XC Therm visualized exactly the same data as Toptask, flugwetter.de and Alptherm (AustroControl). These came from the old regions of the Regtherm model and were produced by the German Weather Service DWD.

On 31 March 2024, however, the German weather service will cease its Regtherm production and the above-mentioned offers will no longer be available. At XC Therm we therefore operate the Regtherm ourselves from January 2024 with more resolved and many new regions. XC Therm will soon have over 1000 refined regions throughout Europe.

Yes, the typical sink rate of the glider is already deducted in the thermal climb rates. This means that you can expect to climb with the indicated speed.

The potential flight distance for each region is the distance in km that can be covered within a full day according to the thermal forecast. It is displayed on the overview map of the thermal forecast.

For the computation of the potential flight distance for every 30 minute interval, the following parameters are considered:

The primary focus of XC Therm and the underlying Regtherm model is to provide a forecast for thermal quality. The output of the Regtherm model contains some wind values, but since only wind values from one grid point of the ICON-Model are available per region, this is by far not sufficient for flight planning in mountainous regions.

Example: The region Urner Alpen extends from the Gotthard Pass to Vierwaldstättersee, and from the Brünig Pass to the Klausen Pass. This corresponds to a radius of over 60 km. The grid point from which the wind values are obtained is approximately in the middle of the southern Lake Vierwaldstättersee. While the regions were carefully selected such that the thermal conditions are homogenous, the wind values within this region can differ significantly.

For that reason, XC Therm provides the high-resolution ICON-D2 wind and weather forecasts for free.

Numerical weather forecast models are rather generic models that are designed to cover a broad range of applications. Many of the parameters that are essential for a high-quality thermal forecast are not considered by such models, mainly for capacity reasons.

The Regtherm model on the other hand is a specialized thermal forecast. Regtherm is not a standalone weather model however, but builds on top of numerical models instead. By adding thermal-specific parameters to these models, Regtherm computes a thermal forecast optimized for gliders, paragliders, hang gliders and rigid wings. This type of model is called a post processing model or coupled model.

More technical details about Regtherm are available here.

The wind and weather forecasts are updated every 3 hours.

The time of the last update is visible in the status line in the lower right corner.

ICON-D2 forecasts are available for max. 48 hours. You can expect that the forecasts for the current as well as the following day are from the high-resolution ICON-D2 model. Days 2-4 are computed using the ICON-EU model.

Zooming in on the wind maps, you can optically distinguish ICON-D2 from ICON-EU data based on the distance between the wind arrows. The arrows on an ICON-D2 forecast are around 2 km apart, while on an ICON-EU forecast they are around 6.5 km apart.

XC Therm was specifically designed for the needs of paraglider, hang glider, and rigid wings pilots. Because it is highly unlikely that some pilots will still fly with winds stronger than 45 km/h, we do not distinguish higher wind values with a different color. This helps maintaining clarity.

The exact wind values however can be seen anytime by tapping or clicking on the wind arrows.

As the pressure differences in these charts only consider the surface pressure, they fail in forecasting Foehn and downslope windstorms in other places in multiple circumstances. Especially on days with inversions they don't provide good information about the conditions at higher altitudes of the passes over the Alps, where Foehn initiates. In addition, together with surface pressure, also the temperature and humidity in higher altitudes play an important role for determining the occurrence of Foehn. Therefore, we consider pressure difference charts only as a rough indicator for Foehn.

On the other hand, the high-resolution wind forecasts of the ICON-D2 model include all the parameters listed above and therefore are much more reliable for prediction Foehn, specifically at altitudes of 1500 m and 2000 m.

The ICON-D2 model does not only have a high resolution horizontally (2km grid), but also vertically. The atmosphere in ICON-D2 is divided into 65 model levels. However, these model levels are only parallel to the ground at high altitudes. Close to the ground, they follow the relief. Therefore, the model levels cannot be used for extracting wind values at a fixed altitude.

In order to make life easier for weather forecast providers, in addition to the model levels, the German Weather Service DWD also offers already precalculated forecasts for some pressure levels relevant for hang gliders, e.g. at 850 hPa (1458m) and at 700 hPa (3013 m). This however creates 2 problems:

1. The actual altitude of the pressure level depends on the air pressure. At a high- or low-pressure situation, the altitude may differ by up to 150 m in both directions. Therefore a 3000 m forecast corresponds to a 2850 m - 3150 m forecast in reality.
2. The published pressure levels in ICON-D2 are too far apart for hang gliders. For instance, the important pressure level at 800 hPa (about 2000 m) is missing.

Some providers solve this problem by interpolating the 800 hPa forecast from the weighted average between the published 850 hPa and 700 hPa forecasts. By doing so, the high vertical resolution of ICON-D2 is lost, as the following picture shows:

Other providers use for the calculation of the 2000 m forecast the model levels and use wind values from the nearest model level. This already is a big improvement because the model levels at an altitude of 2000 m are only around 150 m apart over the flatlands.

XC Therm however goes one step further: We download the whole ICON-D2 model with all model levels and use the same complex calculations (interpolation) that is also used by the German Weather Service DWD in order to calculate wind values exactly for the desired altitude. This allows us to create high-detail wind maps for any altitude, both over ground (AGL) and above Sea level (AMSL). The only limitation is the computing capacity of our servers.