An alternator problem?
This does not sound to me like an alternator problem.
The usual alternator problem is a failure to charge, followed by the starter turning over too slowly and then not starting at all.
This sounds to me like a bad spark plug wire problem (dampness and cold could affect a with a crack in the insulation) or a fuel delivery problem.
Perhaps by some mystical system the alternator is affecting the computer somehow, but this sounds like a lack of spark or a lack of fuel problem.
To find an arcing sparkplug wire, start the car at night in the dark and look for sparks along the wires. Rev the car up (watch out for that fan and don't touch a wire with an ungloved hand).
One easy fix might be to replace the fuel filter. They are cheap and pretty easily changed.
If your car is a Diesel, pay no heed to the sparkplug wires: Diesels are spark-free since 1892. No plugs, no wires, ignition is handled by compression alone once the glowplugs have done their part.
I am not a professional mechanic, but this sort of problem I have fixed myself before with new wires and/or a new filter.
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
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