Run in the midday.
Cold: average high 34°F, low 28°F. Layering becomes the workout. Humidity averages 87% — the limiting factor on most runs. Expect 18 rain days — plan around the radar. Subfreezing mornings mean midday is the only reliably runnable window. Layer up and watch for wind chill.
What December feels like in Helsinki
Sunrise
10:16
Mid-month average
Sunset
16:14
Mid-month average
Time-of-day breakdown
Coolest, driest air of the day. The window before sunrise is the most reliable comfortable hour.
Often the warmest few hours of a cold day. If you can only run once, midday gives you the most temperate window.
Cold drops back in fast after sunset. Tight window — done before headlamp territory.
What to wear running in Helsinki in December
The kit for December in Helsinki: cold-weather layers, gloves, and ear coverage on most mornings, a wind-blocking layer for exposed routes, a water-resistant cap or jacket on standby.