I agree, historic weather is a most essential feature for me.
Being limited to live weather is problematic if
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you want to fly at a certain time of day in the sim and/or in a certain time zone
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you want to fly at a certain time of year in the sim
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you want to practice the same scenario repeatedly several times
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you want to relive the weather you experienced once in real live
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you need to pause the sim (at least if you pause for a prolongued time)
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you use time compression / accelerated sim rate
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you need to save the flight midflight and continue the flight another day
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etc.
In all these cases live weather would just be plain wrong.
If you change the time of day or the time of year in the sim the live weather is completely unrealistic. So now we are forced to bother with manually changing the weather from the user interface which not only takes some effort but also takes away from the immersion a lot (in particular because you can’t even create different weather for different locations). I don’t like flying with scripted weather I created myself, I’d rather have the variety and imponderability of real world weather - but realistically according to the time of day and time of year I chose in-sim.
What I’d like to see is the weather changing according to real world historic weather data in sync with the in-sim time and date. We’ve had that in P3D with Active Sky for years and I used it all the time.
Given that Meteoblue offers a large archive of historic weather data I don’t see why MSFS comes without historic weather.