イエローストーン国立公園の月別の天気

The weather in Yellowstone National Park can change very rapidly from sunny and warm to cold and rainy, so it's important to bring along extra layers of clothing which can be used as needed. Snow can fall in Yellowstone at any time of the year. * Summer: Daytime temperatures are often in the 70s F (25 °C) and occasionally in the 80s F (30 °C) in lower elevations. Nights are usually cool and temperatures may drop below freezing at higher elevations. Thunderstorms are common in the afternoons. * Winter: Temperatures often range from zero to 20 °F (-20 to -5 °C) throughout the day. Sub-zero temperatures over-night are common. The record low temperature is . Snowfall is highly variable. While the average is per year, it is not uncommon for higher elevations to get twice that amount. * Spring & Fall: Daytime temperatures range from the 30s to the 60s (0 to 20 °C) with overnight lows in the teens to single digits (-5 to -20 °C).…

Yellowstone forum threads describe January as extremely cold, with posters citing temperatures well below 0F at times and consistently warning it's an unforgiving combination of deep snow, bitter cold and wind. Road access is dramatically reduced this time of year - only the route from Mammoth to Cooke City stays open to wheeled vehicles, reached via the north entrance at Gardiner, with the rest of the park accessible only by snowcoach or similar. Posters were clear this is a genuinely different park in winter, with different wildlife visible than in summer, and repeatedly recommended a snowcoach day trip to Old Faithful or the Canyon as a standout way to experience it despite the harsh conditions.

Yellowstone-forum threads on February describe this as genuinely one of the most scenic months for a winter visit, posters calling the geothermal features dramatically more striking with steam rising against snow and ice. Regulars call most roads closed to regular vehicles this time of year, a snow coach the standard way to reach Old Faithful and Norris Geyser Basin. Regulars describe wildlife as considerably more visible in February, animals pushed into lower valleys like Lamar making sightings genuinely easier than in summer. Posters call this the start of wolf mating season, pack activity and territorial behavior both more observable now. Regulars recommend a proper expedition-grade coat and real layers regardless of how short outdoor stops are, wind chill genuinely severe. Posters call a guided snow coach tour worth the cost for anyone unfamiliar with winter logistics. The record: -2.6C days feeling like -8C, -15.4C nights, 70.5mm across nearly 12 days and 80 percent humidity.

Yellowstone forum regulars are direct that March is close to the worst month to plan a visit around, not a shoulder-season bargain: nearly all interior roads close March 15, and the park sits in the gap between the winter snowcoach/snowmobile season and the summer driving season. The only major site reachable this time of year is Mammoth Hot Springs near the North entrance — Old Faithful, the geyser basins, and the Grand Canyon of the Yellowstone all sit in the closed zone. Roads that stay open get plowed daily against drifting snow, and posters recommend snow tires as close to mandatory. Regulars steer March visitors toward Zion or Bryce Canyon instead if the calendar is flexible. Our record: -1.2°C days, -8.6°C nights and 61.9cm of snow — genuinely brutal winter conditions, backing the “wrong month, most of the park is shut” read completely.

Yellowstone-forum threads on an April visit describe interior roads as genuinely opening on a staggered basis, posters naming the third Friday of the month as the historical start. Regulars call Mammoth Hotel and Cabins along with Old Faithful Snow Lodge as typically opening around the twenty-fourth, several posters naming this the real point when more lodging becomes available. Posters call the Lamar Valley road between Mammoth and Cooke City the real standout for wildlife, several regulars naming it the best route for wolf viewing alongside bears, bison, bighorn sheep, elk and coyotes. Regulars call the park genuinely not fully open in April, several threads naming closed gates, lodging and visitor centers as real limitations this early. Posters recommend May instead if bear sightings matter most, several regulars calling this the honest tradeoff for visiting in April rather than waiting. The record: 6.6C days, -9.3C nights, 57.4mm across over 11 days and 73 percent humidity.

Yellowstone-forum threads on a May visit describe the stretch from the third Friday of April through most of May as genuinely cold, posters calling not all roads and sights open yet during this window. Regulars recommend avoiding anything much earlier than May 20 for a spring trip, real risk of snow on roads and trails before that point. Regulars call lodging inside the park a genuine advantage for anyone touring multiple areas, cutting down drive time between geyser basins and wildlife-viewing stretches. Posters recommend planning a loop that balances lodges rather than backtracking, several forum regulars offering specific route suggestions based on which roads have reopened. Regulars call real layers essential regardless of a sunny afternoon, May mornings here still capable of a hard freeze. The record: 11.5C days feeling like 10C, -4C nights, an extraordinarily high 58.3mm across over 12 days and 58 percent humidity.

Yellowstone-forum threads on July weather call it the most reliable stretch of the year here, warm, sunny days that regulars still pair with a genuine overnight chill - temperatures can drop right near freezing after dark even as the afternoon runs comfortably warm. Posters describe a fairly common daily arc: a clear, mild morning, a warm midday, an afternoon thunderstorm that can drop hail with little warning, then a cool evening. The standing packing advice across threads is real layers regardless of the forecast - shorts and a t-shirt for the hike, a proper jacket for camp once the sun drops. July is also repeatedly named the best-weather month of the surrounding season, ahead of both June's lingering snowmelt and August's afternoon smoke risk some years. The record: 23.8C days feeling like 21C, 4.1C nights, just 22mm across 5.9 days, 47 percent humidity and 13.5 hours of sun.

August in Yellowstone starts at the hottest the park gets and cools steadily from there - warm days, nights that drop hard, and, regulars are careful to add, snow flurries and freezing nights entirely possible in mid-August. Our row backs them: a 22.3C day against a 4.4C night that feels like 2C, and 0.3cm of snow inside the monthly normal. The crowd shape is the other reason to read the month in halves. The first three weeks are very busy with families; the crowds thin from mid-month as school and college start, and the last week sees roughly 100,000 fewer visitors than July. The wildlife follows the same curve, animals coming back down as the high country cools. The record: 7 precipitation days carrying 37.3mm, humidity 51 percent and 12 hours of sun.

Yellowstone in September splits in two, and the forum is precise about where the line falls. Through roughly the first three weeks the crowds are barely different from summer and the days are pleasant — highs near 17°C with cold nights around 5°C, and the elk rut still running. From about the third week visitor numbers drop away properly, but so do the services: park lodges start closing after Labor Day, and wintry weather can arrive with road closures behind it. Snow is not the September norm, but the park does average some each September, so it is a real possibility rather than a freak event.