For flights under 60 minutes to destination then meters must be considered, the lowest is controlling. So no you still can’t launch with TAF under mins.
If you’re going to argue that “unforeseen circumstances” weren’t unforeseen because charts showed this WX was forecast then I think you will lose that every time. Circumstance had to have been known in time for a schedule change to avoid. Schedules come out the month prior.
In short, WX, MECH, ATC, you can be extended, you may opt out, your options for that vary with airlines.

Found it, thanks to the guy that posted the site with the legal interpretations.

https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/Data/interps/2014/Yu-Southwest%20Airlines%20Pilots%20Assoc%20-%20(2014)%20Legal%20Interpretation.pdf

It says it all right there about "automatic extensions." I was talking to my CA during my trip here at PSA, and it is a common belief that extensions are automatic here. Absolutely not true and here's the document that says as much. Spread the good word.

At 9e, our FOM says we automatically accept the 30 minute extension when we sign the release. Seems to match what that letter says.

Yeah the 30 minute extension is automatic and holds no caveats, longer than 30 minutes and they will contact the pic to see if they'll accept the extension. My experience with PSA is that they usually only check with the Captain then assume the rest of the crew falls in with his or her decision.

That being said the only way to not accept the extension without talking to a chief is to call fatigued which is a pretty simple and painless process in my experience.

How is that legal, unless you're already aware of the delay which requires an extension? It's not. Be careful out there.

No, it does not. It specifically says the concurrence may not be prospective. The only time a 117 duty time signature on the release may be used for the 30 minute extension is when the need for the extension is known at the time of signature.

You’re welcome. When I was at the regional level where they played games with extension rules I used to carry a few printouts of the more important interpretations in my kitbag. Now they’re all on pdf, but thankfully my carrier is even more conservative than I am.

What you just described is not a legal extension.

Then your FOM needs to go back to the POI with a copy of the interpretation attached. 14 CFR 121.135(a)(4) says the manual may “not be contrary to any applicable Federal regulation...”

The real question is, who is the brave soul that’s going to risk their career over it?