Thank you, Mrrzy and Helen!

My auto's warning system has been calibrated, and the tires filled,
so now everything is where it is supposed to be.
The timing of that dashboard warning is telling.
I was reminded by an acquaintance that
the change of seasons brings on a sudden temperature change
which can affect tire pressure equally suddenly.
So, although the tires had enough air in them anyway,
there would have been a sudden overnight change
which might have been enough to trigger the dashboard warning.
Anyway, it's done now.