A snapped cable on a torsion or extension system built around 1991 usually announces itself the same way: the door drops hard on one side, or it won't move at all and the opener just strains against it. Sometimes you'll see the cable itself, frayed and sticking out near the bottom bracket, before it fully lets go.
On houses from this era, the more common early warning is a door that runs crooked - one corner higher than the other - for a week or two before the cable actually parts. That's the strand wearing through, not snapping clean. If you catch it at that stage, it's a planned repair instead of an emergency one.
The heat band here runs moderate, not the extreme swings some parts of the country deal with, so cable failure in this area tends to be plain fatigue and corrosion over time rather than sudden metal stress from a hard freeze-thaw cycle. That's worth knowing because it changes what we check first when we get there.