The San Bernardino Mountains (along with the adjacent San Gabriel and San Jacinto Mountains) are a humid island in the mostly semi-arid southern California coastal plain. Parts of the San Bernardino Mountains have annual precipitation totals in excess of 40 inches (e.g. Lake Arrowhead and Barton Flats areas), and provide an important water resource for the coastal plain below. Most of the precipitation falls between November and March; summers are mostly dry except for infrequent thunderstorms during late summer. During the colder winter storms, snow can fall above 3,000 feet, but most usually falls above 5,000 feet. Ski resorts (mostly in the Big Bear area) capitalize on this snowfall, the most reliable south of the Sierra Nevada Mountains.