Roof Failures and Winter Storms
In normal circumstances, water ingress is a slow seeping build up of dampness over a long period of time and for that reason often continues, unnoticed, until there is a rot outbreak or structural failure.
High winds and driving rain will release a sudden deluge of wet that is immediately obvious. This has the benefit of alerting the property owner of a problem and speeding the remedial work.
Lead flashings, gutters and valleys are all vulnerable areas.