A key factor that will affect your trip to the park in any season is weather. Because of the park's high elevation and its extreme range of elevations, you'll find that temperatures and other weather conditions will vary greatly. Essentially, the higher into the mountains you go, the cooler and wetter it gets. Rangers say that for every 1,000 feet in elevation gain, you can expect a climate change equivalent to that of traveling 600 miles north, and an accompanying temperature drop of 3°F.
The tree line in the park -- the elevation at which trees can no longer grow -- varies somewhat but is generally set at about 11,500 feet. Also complicating the weather picture is the Continental Divide, which runs northwest to southeast through the park. It accounts for markedly different weather patterns -- one on the east side near Estes Park and the other on the west side in the Grand Lake area. Usually the east side is somewhat drier and warmer than the west side.
Particularly at the higher elevations, windchill factors can be extreme. Hypothermia can be a problem at any time, even in summer, when afternoon thunderstorms occur without warning, causing temperatures to drop dramatically and suddenly. Winds of 200 mph are possible in the higher mountain areas at any time of year, and wind speeds of 150 mph have been recorded along Trail Ridge Road.
In summer, temperatures typically climb into the 70s and low 80s (20s Celsius) during the day and drop into the 40s and even 30s (single digits and below 0° Celsius) at night. July is the warmest month and usually sees an inch or more of rain, whereas August is the wettest month of the year, with about 2 inches of rain. Afternoon thunderstorms occur throughout the summer and pose a danger to people on unprotected ridges and in other open places.
Winters usually see high temperatures in the 20s and 30s Fahrenheit (-6°C to 4°C) and lows from 10° below zero to 20° above (-23°C to -7°C). January is the coldest month, although February may feel colder because of gusty winds that seem to cut right through you. November and December usually have only light snow, but the amount of snowfall increases through January, February, and March. Spring and fall temperatures can vary greatly, from pleasantly warm to bitterly cold and snowy. For this reason, spring and fall are when you need to be the most flexible and ready to adjust your itinerary to suit current conditions.
