I never used custom weather. Always fly with live weather. So I’m actually no expert on this. But I can tell you, that you can switch the settings of the weather source in the EFB to MSFS weather. Which should be the weather current in MSFS (and it should be your custom weather). So you can read the weather from the EFB main page and fill in the MCDU.
See here for more:
https://docs.flybywiresim.com/fbw-a32nx/feature-guides/flypados3/settings/#atsuaoc
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