Winter — November through March — is the classic time to visit for the aurora, and January is the most likely month for clear, dark skies. Temperatures regularly reach −36°C, occasionally lower; the wind off Russia makes it feel colder. This is not a drawback if you are prepared, but it is not a place to improvise cold-weather gear.
Summer, particularly around the solstice in June, offers the opposite phenomenon: very short nights, a sky that barely fully darkens, and long evening light over the Amur. The mosquitoes in this season are the serious obstacle — the boreal forest in summer produces insects of a dedication and quantity that most travelers find memorable for the wrong reasons. Autumn is perhaps the most balanced season: the colours of the taiga are excellent, the insects are gone, and the first aurora windows are opening.