It's usually raining in Napa during the winter. The vineyards are bare,
the tourists are gone, and the hot springs are empty (of people). It
may not sound like it, but this is a great opportunity to take pictures!
Why? Because since grapes only grow in the spring and summer, the ground
is cultivated by planting mustard flowers along the rows between the
grape vines, which makes for wonderful scenery. There's also usully some
low fog and rains which can add mood and character to your pictures,
not to mention aid in color saturation.
Why do they plant mustard flowers in grape vineyards, you ask?
The plants help stimulate the soil, helping the grapes grow better
in the summer. This is much the same principle behind why the White
House needs interns. You may not like it, but you get better grapes
in the end.