UPDATE: According to the official MSFS Forums, the recent Live Weather bug has been fixed on the server-side. Remember, to avoid the “Live Weather not loading at all” bug, always load your flight with Clear Skies weather preset, and after the flight has loaded and you’re sitting in the cockpit, activate the Live Weather from the upper custom toolbar.
The default Live Weather that comes with the latest Microsoft Flight Simulator utilizes the internal weather simulation means in full capacity, providing local wind, temperature, and air pressure data from METeorological Aerodrome Reports, METARs. Other data such as all the clouds, upper weather conditions, winds aloft, and prediction services are provided by Meteoblue. Sometimes, the Live Weather seems not to work, or some of the data is missing due to server updates or changes made because of upcoming releases. There are two weather add-on alternatives if searching for real-world weather injection into the sim, freeware Unreal Weather – Live METAR and payware REX Weather Force 2020.
Both Unreal Weather and REX Weather Force are limited to the data model available on the Weather Settings menu. It, for example, cannot recreate different weather zones around the player, so the weather will always appear uniform in every direction. Both add-ons support smooth, user-configurable transitions between weather stations to provide the best experience. In addition, REX Weather Force also provides upper-temperature changes and winds aloft. The cloud data injects from the closest airport METAR data, so there are no upper cloud layers generated. For me, the smooth weather transition feature made a noticeable frames-per-second hit, so I prefer to use the instant weather load instead.
Remember, to avoid the “Live Weather not loading at all” bug, always load your flight with Clear Skies weather preset, and after the flight has loaded and you’re sitting in the cockpit, activate the Live Weather from the upper custom toolbar. Also, if you want the exact correct time into the sim, once in a cockpit, you need to click the LIVE button below the clock time slider. For a non-live weather condition add-on, I do recommend the SoFly Weather Preset Pro containing dozens of new and different weather presets from a hurricane to sandstorms. For example, land at difficult airports in almost zero visibility or test out your skills with gusty winds sweeping your aircraft from side to side.