Peter wrote:


These sources may be "authorised" but is there anything in the FARs
which makes the sourcing of weather data from other providers illegal?

This is particularly relevant to N-reg aircraft flying outside the
USA... they do that sometimes

No one cares unless there is an accident or serious incident. If there
is, which involves weather, and there is no record of an official
briefing, the FAA can reasonable conclude that you failed to obtain the
necessary preflight information. The burden is upon the pilot (or his
estate~) to prove compliance when there is no FAA or approved vendor record.

The biz jets that often fly outside the U.S. invaribly use one of the
approved vendors on that FAA list.

The U.S. air carriers have their own approved weather services so they
are always covered.