The lowest temperatures usually occur between December and February in all parts of Switzerland. At most measurement sites, January is generally the coldest month of the year. The greatest variability in temperature is found in winter.

Across most of Switzerland, January is consistently the coldest month of the year. During this time, the country is firmly in the grip of winter, with average temperatures in low-lying cities like Zurich, Geneva, and Basel hovering between -2°C and 3°C (28°F to 37°F). In the high-altitude Alpine regions, such as Zermatt or St. Moritz, January temperatures are significantly colder, often dropping to -10°C to -15°C (5°F to 14°F) or lower at night. This month sees the most consistent snowfall, making it the peak season for winter sports but also the time when the "Bise" (a cold, dry wind from the northeast) can make the perceived temperature feel much lower. While December can occasionally be warmer due to the "Föhn" wind, and February is often just as snowy, January remains the statistical "heart" of the Swiss winter. For travelers, this means shorter days and the need for high-quality thermal layers, though the crisp, blue-sky days in the mountains provide some of the most spectacular scenery of the year.