Snow can fall in any month, but it doesn't usually stay on the ground until September. By June 1, the snow has begun to melt, but the active layer remains frozen. The sun remains above the horizon for 24 hours each day, and plants are producing new growth. Autumn has come to the tundra. The air is cooler, and plants are finishing their growth for the year.
Air temperatures are now below freezing, and the soil surface begins to refreeze.
The soil surface continues to freeze down into the active layer. The soil above it is refreezing rapidly. By November 1, there is just a narrow region above the base of the active layer that is not frozen. By November 15, the active layer has completely frozen, and will remain this way until early summer.