The frost/snow is where it is the coldest. In
other words, all of the roof is colder than the
are where the frost is. The area where the frost
is either the area of best insulation or most
ventilation. Your neighbor should wish that all
of his roof look like what you call wet spots.

It *is* a wet spot when it's not below feezing. It is obvious that the
shingles are wet in this one spot in the morning. They dry durig the
day, but the next morning they are wet again.

Angie