An aging roof
A roof rarely fails on a single day. It gets close over several years, and then one storm finds the weakest point.
Granules in the gutters
The mineral surface on an asphalt shingle protects the asphalt from ultraviolet light. A new roof sheds a little loose material in its first months. A roof that is filling the bottom of a downspout with granules year after year is losing its protection, and the asphalt underneath hardens and cracks once it is exposed.
Curling, cupping and cracking
Edges lifting away from the roof, corners turning up, or shingles that look wavy across a whole slope all indicate the mat has lost flexibility. A shingle in that state cannot seal to the one below it, which means the next wind event has something to catch.
Uniformity matters. Damage in one area is a repair. The same appearance across an entire slope is the roof telling you its age.
Whole streets come due together
In developments built out in a single phase — much of Fairfax, Ashburn, Nottingham, Bel Air — the roofs went on within a couple of years of each other and reach the end of their life within a couple of years of each other. One neighbour replacing a roof is frequently followed by several more on the same block within a season, and it is a reasonable prompt to have your own looked at.