For weather forecasts, crop planning, and heating bills, winter starts on December 1st —a full three weeks before the solstice.

The start of winter can vary significantly depending on the region:

Ultimately, winter isn’t just a date on a clock or a line on a map. It’s a feeling—the first time you see your breath in the air, the first flake that sticks to the ground, or the first night you have to scrape frost off your windshield. By that measure, winter starts exactly when it arrives at your front door.

Frustrated by the astronomical calendar’s shifting dates (which made climate data messy to compare), meteorologists and climatologists created a simpler system based on the annual temperature cycle.