Frequently Asked Questions - FAQ

General

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.

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.

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

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.

Subscriptions

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.

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

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.

Thermal Forecasts

For the thermal climb rates, the typical sink rate of the glider is already deducted. 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:

Climb Rate

The climb rate in a thermal region decides, if and how quick altitude can be gained. They have a big influence on the potential flight distance.

If the average climb rate in a 30 minute interval is smaller than 0.8 m/s, no kilometers are added to the total flight distance for that time interval.

Usable Altitude

The usable altitude is the thickness of the layer, in which climbing is expected.

If the usable altitude is smaller than 900 meters for a 30 minute interval, no kilometers are added to the total flight distance for that time interval.

Wind

Depending on the planned flight task (see below), wind can extend, shorten, or completely prevent a cross country flight.

Aircraft
(configurable)

The polar of an aircraft determines the actual glide ratio and therefore how many meters can be covered for each meter of altitude.

In XC Therm, the polars of paragliders, hang gliders, and rigid wings can be selected.

Pilot Skills
(configurable)

The pilot skills is a factor in percents that is applied to the calculated potentiel flight distance. Using this parameter, a pilot can adapt the calculation of the potential flight distance to his flight skills.

Flight Task
(configurable)

XC Therm supports two types of flight tasks: Out and Return and Oneway.

Return means that the pilot wants to return to the starting point of the flight. The stronger the wind, the more difficult this task gets because at least one leg is against the wind. If the wind is too strong, the potential flight distance is 0.

Oneway means that the pilot flies with the wind the whole day as it's usually the case in the flatlands. If there is only little wind, the potential flight distance differs only slightly from a Return flight. But the stronger the wind, the bigger the potential flight distance gets.

Note:

Especially in the setting Oneway., unrealistically big distances can be calculated for strong wind. Therefore Oneway should always be used with care. This is also the reason why this feature is disabled by default.

Attention:

The potential flight distance is an automated calculation given the parameters described above. It should be a indicator about the quality of thermals. Under no circumstances a big potential flight distance should be seen as a flight recommendation. The detailed thermal forecast for each region as well as the high resolution wind forecast should be taken into account when planning a flight.

The following table shows the update times for the thermal forecasts. Because the computation of Regtherm takes a few minutes, the forecasts for the following days are updated with a few minutes delay.

Current Day
Input Data
3:30 UTC
ICON-EU 0Z
5:30 UTC
ICON-EU 0Z
6:30 UTC
ICON-EU 0Z
+1 to +4 Days
Input Data
3:30 UTC
ICON-EU 0Z
15:30 UTC
ICON-EU 12Z

Usually dew forms at night on the ground because excessive humidity condensates due to the cooling-down. This humidity cannot be detected by monitoring stations that are located at 2m above ground and hence is not included in the midnight run of ICON-EU. Therefore, the Regtherm forecasts at 3:30 UTC tend to be too dry and hence the predicted cloud base is often too high and the cloud size too small.

The dew on the ground starts to evaporate with the insolation after sunrise. Once evaporated, this humidity can be detected by monitoring stations again. This is the reason why Regtherm computes two additional runs at 5:30 and 6:30 UTC using the values from the midnight run of ICON-EU that have been corrected by the live measurements.

XC Therm visualizes the exact same data as Toptask, flugwetter.de, and Alptherm. This data is produced by Deutscher Wetterdienst (DWD) using the Regtherm model.

The various offers differ in the number of available regions and their visualization. Toptask and XC Therm offer forecasts for the next 5 days and for all the 289 regions. While Toptask is designed to be used only on a PC and is aimed at glider pilots, XC Therm offers a smartphone-compatible visualization that addresses mainly paragliding, hang gliding, and rigid wing pilots.

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 named Berner Oberland stretches from Rochers-de-Naye at Lake Geneva to Pilatus in Central Switzerland, which corresponds to a distance of 120 km. The grid point, from which the wind values are taken, lies approximately in the middle, at the southern Lake of Thun. 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 at no cost the high-resolution ICON-D2 wind and weather forecasts.

The smaller the grid size of a numerical model, the more computing power is necessary for its calculation. Therefore, the forecast range is shorter for models with a small grid size.

For a 5-day forecast as is offered by XC Therm, ICON-EU with a grid size of 7km is the model with the smallest grid size that still covers Europe for the next 5 days. Models with a 2.2km grid (ICON-D2) are either only computed up to 48h in advance, or they only cover small parts, such as COMSO-2E from MeteoSwiss, which covers 5 days in advance, but only for the Alps.

Comparisons have shown however that there are no significant differences in the quality of the thermal forecasts computed by Regtherm between using ICON-EU or COSMO-D2 as input model.

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. However, Regtherm is not a standalone weather model, but builds on top of numerical models. By adding thermal-specific parameters to these models, Regtherm computes a thermal forecast optimized for gliders, paragliders, hang gliders and rigid wings. This kind of model is called a post processing model.

More technical details about Regtherm are available here.

Wind and Weather Forecasts (ICON-D2)

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.

On the wind maps, using the biggest zoom level, you can also see that the arrows on an ICON-D2 forecast are around 2 km apart. In 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.

The pressure differences in such forecasts are predicted on the ground. However, especially on days with inversions they don't provide good information about the conditions at the altitudes of the passes over the Alps. In addition, also the temperature and humidity in the altitude play an important role for occurrence of Foehn. Therefore, we consider pressure difference charts as only 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 better suited 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.

ICON-D2 Model Levels
The model levels of ICON-D2 seen over a cross-section over the Alps.

In order to make life easier for weather forecast providers, in addition to the model levels, the Deutsche Wetterdienst (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:

ICON-D2 Vertical Resolution

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 Deutsche Wetterdienst (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.