A grid of 16×16 weather envelopes make up the X-Plane weather system. Each of these 256 weather “buckets” is about 1.0 degrees of longitude by 0.6 degrees of latitude, or about 35 miles or so. Custom weather can be created by modifying the METAR.rwx & winds.rwx files in a text editor. Real weather files are initially downloaded via the last tab in the Weather screen in X-Plane.
This file contains weather in METAR form at countless airports, but with a far higher density in the USA. METAR data contains weather at the surface, with cloud bases for various elevations above the airport. X-Plane can only guess at cloud TOPS and WINDS ALOFT based on this limited data from the surface.
This file loads custom winds 10,000 ft and 34,000 ft into X-Plane, so you have winds aloft for both light planes and airliners, with interpolation for turboprops that fly in between. (Note that this file is only used if global_turbulence.grib & global_winds.grib are NOT in the main X-Plane folder.)
global_turbulence.grib and global_winds.grib
Starting with X-Plane 10.50, these are GLOBAL winds-aloft files that are also downloaded so you can get winds anywhere on Earth. As with winds.rwx, these files loads winds 10,000 ft and 34,000 ft into X-Plane, so you have winds aloft for both light planes and airliners, with interpolation for turboprops that fly in between.
Modifying the Files
Now, you can make your own METAR.rwx file and winds.rwx file. First turn off the download option in the weather screen so X-Plane does not over-write your file.
To test the files that you make, tie command “sim/operation/load_real_weather” to a joystick button or key to test loading the weather at any moment to scan the files you made, or issue the command via plugin. Or just hit the “read right now” button right there in the real-weather screen.
For global weather coverage of any level of detail you like, add your own entries into the METAR.rwx file. Enter an airport ID of MDEG, followed by the longitude, latitude, and elevation in meters of the imaginary airport you just created for the purposes of setting weather at this location.
For example, if we wanted to change the weather for the South Carolina area, we would specify the area in the METAR.rwx file as: “MDEG -81.235425 34.5647 80.0”. After that we’d enter the information for our weather, such as “24031KT 2SM CLR 10/M10 A3011”.
Let’s parse the first few items in our example above. Note that X-Plane uses longitude first, then latitude; thus the location is 81.235425 degrees West, 34.5647 degrees North. Altitude is 80 meters. The wind direction is 240, with a speed of 31 knots. The visibility is 2 statue miles and the sky is clear (no ceiling). The temperature is 10 degrees Celsius and the dew point is minus 10. The altimeter setting is 30.11inHg. Continue on in this manner when you are adding custom winds or interpreting the report.
You can enter all the MDEG airports you like in a single file, to set the weather anywhere you like. If you put an MDEG airport every degree of longitude and every half degree of latitude, you will be entering about the right number of MDEG airports to get all the detail you can out of the X-Plane weather engine.
Note that if you are customizing weather for an airport that is already listed in the METAR file you will need to delete all other instances aside from your MDEG entry.
For global coverage of any level of detail you like, you can add your own entries into a winds.rwx file. If you do not have one from an older version of X-Plane 10, you can simply start a new text file. Make sure to remove the global_turbulence.grib & global_winds.grib files to avoid conflicts.
In winds.rwx, enter a wind reporting-station ID of DEG (NOT MDEG! These are 3-letter IDs!), followed by the longitude, latitude, and winds aloft, then X-Plane will set the winds aloft at this location as you enter.
Each of the numbers after the latitude represent the direction, speed and temperature. Each column of wind information corresponds to a specific altitude: 3000, 6000, 9000, 12000, 18000, 24000, 30000, 34000, and 39,000 feet. Note that you may leave a lower altitude column blank if the location is already above that altitude.
DEG -82.235 34.345 2910 3117+14 2925+08 2934+04 2924-07 2836-20 284436 284946
Let’s parse the first few items in our example above. Note that X-Plane uses longitude first, then latitude; thus the location is 82.235 degrees West, 34.345 degrees North. At 3000 feet, the wind direction is 290, with a speed of 10 knots. At 6000 feet, the wind direction is 310, speed 17 knots, and a temperature of +14 degrees Celsius. Continue on in this manner when you are adding custom winds or interpreting the report.
Enter all the DEG wind-reporting station you like in a single file, to set the weather anywhere you like. If you put DEG wind-reporting station every degree of longitude and every half degree of latitude, you will be entering about the right number of wind-reporting station to get all the detail you can out of the X-Plane weather engine.
NOTE: YOU MUST ENTER A FULL WINDS-ALOFT REPORT AT ALL THE ALTITUDES YOU SEE IN THE DOWNLOADED WINDS.RWX FILE FOR IT TO BE READ!
X-Plane will only USE the data at 12,000 ft and 34,000 ft (with interpolation in between them) but you have to ENTER all altitudes for the wind file to be scanned properly. (It’s valid to use a dummy value such as 0 for all data at all altitudes that are not 12,000 ft and 34,000 ft.)