The climate of the area often varies significantly due to the abundance of microclimates characterizing the region. San Diego–Tijuana's topography, bays, coastal hills, mountains, canyons and gorges maintain their own climates while being relatively near to each other. During the May gray and June gloom seasons, a dense cloak of coastal clouds, known as marine layer, covers the coastal areas, keeping the area cool and moist to up to inland. This coastal cloud cover is frequently observed reaching as far inland as Poway and in some cases, San Diego Country Estates. Yet once outside this cloud, the weather in sharp contrast can be warm and sunny. In some cases, June gloom lasts into July, creating cloudy skies over the coastal regions for entire days.