Knowledgebase Simulation: Weather

Scope

This page collects different information regarding weather creation and injection into an arbitrary simulator. The first version is a collection of information which was gathered over the last couple of weeks/months. It contains weather and METAR sources, API information and techniques required to implement a sophisticated weather engine. For the time being this page is a central place to store and share knowledge.

Roadmap

Currently a very basic and simple version of a weather engine is implemented in swift. We do not plan to implement a sophisticated weather engine, but a simple one for those who have no other engine.

You can enable/disable *swift weather from settings.

Weather Sources

The following real weather sources exist and can be used to retrieve real time data. They are listed in the order of priority how they should be used.

Global Forecast System (GFS) Model

The Global Forecast System (GFS) is a global numerical weather prediction system containing a global computer model and variational analysis run by the US National Weather Service (NWS).

The mathematical model is run four times a day, and produces forecasts for up to 16 days in advance, but with decreased spatial resolution after 10 days. The forecast skill generally decreases with time (as with any numerical weather prediction model) and for longer term forecasts, only the larger scales retain significant accuracy. It is one of the predominant synoptic scale medium-range models in general use.

GFS products are available for any position on earth and can be retrieved via http://www.nco.ncep.noaa.gov/pmb/products/gfs/. This turns it into a perfect weather source candidate for areas with no ICOA stations available (areas above the oceans, etc.)

VATSIM METAR

It is generally possible to query the METAR string for a given ICAO airport. METAR is only valid for a small area around the airport and has a lot less information compared to the layers described above.

VATSIM Weather

VATSIM server provide the ability to request detailed weather information for ICAO stations around the globe. On request it will provide the following information.

Wind Data (4 layers)

.Ceiling ^ .Floor ^ .Direction ^ .Speed ^ .Gusting ^ .Turbulence ^

Cloud Data (2 layers)

^ .Ceiling ^ .Floor ^ .Coverage ^ .Icing ^ .Turbulence ^

Cloud Data (4 layers)

^ .Ceiling ^ .Temperature ^

This data is produced from a simple extrapolation from the airport METAR. It is therefore very inaccurate and usage is not recommended.

Simulator Interfaces

Microsoft Flight Simulator Family

The Microsoft Flight Simulator family offers several ways to inject used defined weather into the simulator.

FSUIPC - New Weather Interface (FSX and FS2004): The NWI allows to write weather details per station into the simulator. Usually you should set GLOB weather first and then every ICAO station in the range of 40 nm.

http://www.schiratti.com/dowson.html

SimConnect (FSX): SimConnect allows to set weather per station via an extended METAR string. See https://msdn.microsoft.com/en-us/library/cc526983.aspx\#SimConnect\_WeatherSetObservation

Weather Theme Files (FSX and FS2004): Weather theme files (WTB) are binary files which contain a very detailed description of the weather around the user aircraft. It is independent from any ICAO station. In the first place weather theme files were used to save used defined weather, created inside the simulators itself. The user was able to setup a scenario on his own and load it. Actually all saved conditions (CAVOK, storm, etc.) which you can choose when starting MSFS are stored as WTB files. The FS2004 Weather Themes Software Development Kit is a Visual Basic application which allows the user to also setup weather scenarios outside of MSFS. Luckily both simulators - FSX and FS2004 - support these WTB files and even better they can be loaded at runtime via FSUIPC (TBC) and SimConnect SimConnect_WeatherSetModeTheme. This files can be created and loaded by any external application and then loaded into FS. The file format is proprietary but is successfuly reversed engineered and a library to read and write these files is available libwtb - written by me, so we have full control.

X-Plane

X-Plane DataRefs: The weather in X-Plane can be configured via the datarefs in sim/weather/. Unfortunately it does have only 1D vertical layers, which means you can configure only global weather with different altitude layers.

Reference Implementation

• XplaneNoaaWeather
• python based X-Plane weather plugin licensed under GPLv2.