For a person who lives at a latitude of +40 degrees (ukiah for example), when is the sun directly overhead at noon

The answer is - Never.

40 degrees of latitude, be it on the southern or northern part of the Earth, never gets direct sunlight throughout the year. This is due to the fact that the Earth's inclination is not that big so that the sunlight can fall directly on this latitude, in fact, the inclination of the Earth allows the sunlight to fall directly on the surface only to the lines of 23.5 degrees north and south of the Equator.

Where are they though?