Yellowstone National Park sits at over 7,000 feet elevation in the Rocky Mountains, making its weather more extreme and unpredictable than most parks. Using Perfect Weather Index (PWI) scores calculated from daily National Weather Service forecast data, this page shows exactly when conditions are most comfortable for wildlife viewing, geyser watching, and hiking — and when winter closes most of the park entirely.
Current Perfect Weather Index scores for the next 7 days at Yellowstone National Park. Higher scores indicate more comfortable outdoor conditions. Updated daily using National Weather Service forecast data.
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How to use this: Days with higher scores are generally better for hiking and outdoor activities, with more comfortable temperatures, lighter winds, and fewer weather impacts. → View official National Weather Service forecast for Yellowstone
July offers the most consistently comfortable weather at Yellowstone National Park, while June and August provide excellent conditions during the peak summer season.
Based on 2025 Perfect Weather Index (PWI) data from the Old Faithful area (elevation ~7,300 ft), Yellowstone shows a classic high-altitude Rocky Mountain pattern: a long, cold winter with limited park access, a rapid spring thaw with variable conditions, an excellent summer window, and a quick descent into fall cold from October onward.
Raw monthly totals were normalized into monthly PWI scores (percent of possible points) and paired with the number of rare Perfect 10 days.
Monthly PWI scores reflect the percentage of possible comfort points earned at Yellowstone across all days in each month, based on 2025 National Weather Service forecast data. Perfect 10 days are days scoring a full 10 out of 10 on the PWI scale.
| Month | Monthly PWI Score | Perfect 10 Days | What It Means | Verdict |
|---|---|---|---|---|
| January | ~50% | 0 | Deep winter, extreme cold | Avoid |
| February | ~44% | 0 | Coldest, least comfortable | Avoid |
| March | ~50% | 0 | Winter lingers | Avoid |
| April | ~59% | 0 | Slow thaw, limited access | Caution |
| May | ~70% | 2 | Improving but variable | Good |
| June | ~81% | 2 | Excellent early-summer weather | Excellent |
| July ⭐ | ~87% | 2 | Peak comfort, most reliable | Excellent |
| August | ~84% | 2 | Warm days, cool nights | Excellent |
| September | ~79% | 2 | Crisp, stable fall weather | Very Good |
| October | ~60% | 0 | Rapid cooling, early snow | Caution |
| November | ~55% | 0 | Cold returns quickly | Avoid |
| December | ~45% | 0 | Harsh winter conditions | Avoid |
PWI scores based on 2025 NWS forecast data at Furnace Creek. Scores at higher elevations within the park will differ.
Monthly visitor counts at Yellowstone National Park (2024, source: NPS). July is both the most visited and the highest-scoring PWI month — but September offers nearly identical wildlife viewing opportunities with 140,000 fewer visitors and strong weather scores.
| Month | % of Annual Visitors | Avg Visitors | Crowd Level |
|---|---|---|---|
| January | 1% | 42,740 | Very Low |
| February | 1% | 49,291 | Very Low |
| March | 1% | 32,862 | Very Low |
| April | 2% | 71,784 | Low |
| May | 11% | 522,450 | Moderate |
| June | 19% | 914,612 | High |
| July ⭐ | 21% | 992,352 | Peak |
| August | 18% | 868,259 | Peak |
| September | 18% | 852,435 | High |
| October | 7% | 346,025 | Moderate |
| November | <1% | 21,133 | Very Low |
| December | 1% | 30,410 | Very Low |
Source: National Park Service visitor use statistics, 2019–2023 average.
July is Yellowstone's top-scoring month at 87% PWI, with the most reliable conditions for hiking, wildlife viewing, and geyser watching. All roads are open, temperatures at the 7,000-foot elevation are comfortable rather than hot, and afternoon thunderstorms — while common — are typically brief. July is also the most visited month, so popular areas like Old Faithful and Grand Prismatic Spring see the heaviest crowds. Book accommodation 6–12 months in advance for July visits.
August scores 84% PWI and sees slightly fewer visitors than July while maintaining excellent conditions. Wildflower season is winding down but wildlife activity remains high. Bison rut begins in late August, creating some of the most dramatic wildlife viewing opportunities of the year. Evenings cool noticeably at elevation, making for comfortable camping and stargazing conditions.
June scored 81% PWI in 2025 — the strongest early-summer month. Wildflowers are at their peak, snowmelt fills the rivers and waterfalls to impressive levels, and most roads reopen from their winter closure by late May or early June. Visitor numbers are high but somewhat lower than peak July. Wildlife with newborn young is common in June, making it one of the best months for animal sightings.
September scored 79% PWI with 2 perfect days — excellent conditions with significantly fewer crowds than summer. Bull elk rut peaks in September, with bugling audible throughout the park and spectacular wildlife viewing opportunities. Fall colors begin in late September at higher elevations. September is widely considered the best month for visitors who want excellent weather and wildlife without peak summer crowds.
May scored 70% PWI with 2 perfect days — a solid shoulder month as spring arrives. Roads reopen progressively through May as snowpack melts. Wildlife is highly active with newborn animals. Weather is variable and snow is possible at any point, but comfortable days are increasingly common by mid-month. Visitor numbers are significantly lower than summer, making May a good option for those who don't mind unpredictable conditions.
Most Yellowstone roads close to regular vehicles from early November through late April. The park transitions to oversnow vehicle access only (snowcoaches and snowmobiles) from mid-December through mid-March — a unique and genuinely spectacular winter experience, but not a casual visit. PWI scores drop sharply from October (60%) through February (44%) as high-altitude cold sets in. October can still offer comfortable days but early snow is common and conditions change rapidly.
Yellowstone sits on a high plateau averaging 7,000–8,000 feet elevation, which means weather is cooler, snowfall heavier, and summer shorter than most visitors expect. Conditions vary significantly across the park's 3,472 square miles.
Afternoon thunderstorms are common throughout summer at Yellowstone's elevation — typically building after midday and clearing by evening. Lightning risk on exposed ridges and boardwalks is real; most visitors plan higher-elevation activities for morning and return to valley areas in the afternoon. Snow is possible in every month of the year at Yellowstone, even in July at higher elevations.
What is the best time to visit Acadia National Park?
September is the best month to visit Acadia based on Perfect Weather Index scores — peak comfort, crisp air, easing crowds, and early fall foliage. August is the best summer month, with the most stable warm conditions. If avoiding crowds is the priority, late May and early October offer respectable weather with significantly fewer visitors.
How cold does Acadia get in winter?
Winters at Acadia are cold and windy. January and February average highs in the low 30s°F (0°C) with lows regularly below 20°F (-7°C). Wind chill on Cadillac Mountain can make conditions feel significantly colder. PWI scores in winter drop to around 49–50%, reflecting genuinely uncomfortable outdoor conditions for casual visitors.
Does Acadia get fog?
Yes — coastal fog is a defining feature of Acadia's summer weather, particularly in June and early July. It typically forms when warm, humid air moves over cold ocean water and most commonly clears by midday. The Schoodic Peninsula on the mainland is often clearer than Mount Desert Island when fog is present. The Perfect Weather Index accounts for cloud cover and visibility in its scoring, so foggy days will score lower than clear days even if temperatures are comfortable.
When does fall foliage peak at Acadia?
Fall foliage at Acadia typically peaks in the first two weeks of October, though timing varies by year. The combination of coastal views, rocky shorelines, and colorful foliage makes early October one of the most visually spectacular times to visit. October also scores well on the PWI (75%), making it a genuinely comfortable month despite the cooler temperatures.
What is the best time to visit Acadia for European visitors?
September is ideal for European visitors — peak weather comfort, fewer crowds than summer, and early fall foliage beginning. July and August are also excellent if summer travel is preferred. Acadia is easily combined with Boston (approximately 5 hours by car) and other New England destinations. Many European visitors fly into Boston and drive up the coast through Portland, Maine on the way to Bar Harbor.
What is the Perfect Weather Index?
The Perfect Weather Index (PWI) is a daily comfort score from 1–10 calculated from National Weather Service forecast data. It combines temperature, sunshine, humidity, wind, and precipitation into a single rating. A score of 8 or higher means genuinely excellent outdoor conditions. Scores below 4 reflect cold, storms, or other conditions that significantly limit outdoor comfort. Learn more about how the PWI works →