Wildlife-viewing is generally excellent throughout the year in the Maasai Mara and Ngorongoro Crater. However, game-viewing opportunities peak from January-April in the southern Serengeti and from June-October in the northern Serengeti. This variation is due to the Great Migration of several million wildebeest, zebra and gazelle. The herds gather in the south to feed on the immense grasslands and to give birth to their young. When the food supply is exhausted and the newborns are strong enough to travel, they begin to head north and west, passing through the Grumeti area from May-July. By August, the herds have reached the northern Serengeti, where they cross into Kenya’s contiguous Maasai Mara to enjoy its lush grazing. In November, they begin the 200-mile trek south to the plains of the southern Serengeti, where the grass is once again lush after the seasonal rains. There the epic cycle begins anew. The times to avoid in Kenya and Tanzania are the long rains in April and May and the short rains in November. The rest of the year, you can typically expect cool nights and warm, sunny days broken by occasional afternoon and evening showers. In recent years, however, weather patterns have become notoriously fickle. The Ngorongoro Crater is subject to cool winter nights (45F-55F) from June-September as a result of its 7,300-foot elevation.