Frost and cracked coverings
Water entering small cracks can freeze and enlarge them. Older tiles and mortar are more vulnerable where the surface is already weathered.
Blocked gutters in prolonged rain
Leaves and moss left from autumn can reduce gutter capacity just when rainfall is persistent. Overflow at eaves is easily mistaken for a leak through the roof covering.
Condensation in the loft
Cold roof surfaces can collect moisture from warm air escaping the house. Damp underlay and droplets on nail points may be condensation rather than rain penetration. Ventilation and indoor moisture levels need looking at alongside the roof.
After snow
Melting snow can reveal blocked outlets or defects that ordinary showers did not. If a leak starts during thawing, mention that sequence when the roof is inspected.