CLIMATE The climate of any part of the world is due to many forces—but basically to the amount of energy received from the sun. In mountainous areas, such as Rocky Mountain National Park, the climate is made more variable by the different altitudes, slopes, and exposure to solar radiation. Like all midlatitude regions, too, the park experiences invasions of different air masses with their varying qualities and the storms associated with their fronts. Few frontal storms are experienced in summer. Most of the frequent thunderstorms are produced by the elevation and cooling warm air from the Gulf of Mexico as it streams into the mountains from the southeast. This season provides the great cumulus clouds that delight the photographer. During autumn, winter, and early spring the weather is determined by alternate invasions of cold Canadian air and cool Pacific air. The latter brings much snow to the western side of the park, but usually results in favorable weather on the eastern slope; the warm chinook winds are associated with these conditions. The Canadian air—usually heralded by blizzards on the plains below the mountains—brings snow and below-zero temperatures to the east slope. The winter weather at the village of Estes Park is often milder than in most of the plains country to the east, because of the protection afforded by the mountains from the full forces of these air movements. In general, the weather is ideal for summer vacations, with cool, clear nights and sunny days. The frequent afternoon showers are mere refreshing interludes in an otherwise delightful season. The winter weather, although often rigorous, is relatively mild for the region’s altitude, and, although the high Trail Ridge Road is snow-blocked, scarcely ever is it a problem to drive from Estes Park village to Denver or other plains communities. It is always cool at night, even in midsummer, so bring warm clothes; western garb is always socially acceptable. The region is noted for its friendly informality. For hiking on trails and camping, old field clothes are desirable, and stout, comfortable shoes are a necessity. A slicker is important, since afternoon showers may be expected. PARK SEASON Although the park is officially open to travel all year, summer—June through September—is the “regular” season. From October until May, high-altitude roads are blocked by snow, as are most park trails in winter. All but one of the visitor centers are closed, and naturalist hikes and other activities are not scheduled after September 15. Camping is difficult from September to May because of adverse weather and limited facilities. However, the roads to both Estes Park and Grand Lake are usually open throughout winter, and accommodations are available in both gateway towns during the off-season. WHAT TO DO