A white Christmas here means at least an inch of snow on the ground on Christmas morning — the National Weather Service’s definition. Chester County has had one in 30 of the 121 years with a reading, about one in four, and the most recent was 2012.

Measure widens that in two steps — snow on the ground on Christmas Eve or Christmas Day (36 years), then any day in the ten days before Christmas (62 years) — or switches to a different question: whether snow actually fell over the 24th and 25th (40 years). Counts when sets how much of the county has to agree.

Snow season totals are on Snow Seasons, the snowiest winters on Top Snowfalls by Season, and the biggest individual storms on Top Snowfalls by Month.