Average Weather in May in Big Sky Montana, United States
Daily high temperatures increase by 8°F, from 47°F to 56°F, rarely falling below 35°F or exceeding 68°F.
Daily low temperatures increase by 8°F, from 24°F to 32°F, rarely falling below 16°F or exceeding 39°F.
For reference, on July 27, the hottest day of the year, temperatures in Big Sky typically range from 41°F to 72°F, while on December 30, the coldest day of the year, they range from 3°F to 20°F.
Average High and Low Temperature in May
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on May. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature in May
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The month of May in Big Sky experiences gradually decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 56% to 51%.
The clearest day of the month is May 31, with clear, mostly clear, or partly cloudy conditions 49% of the time.
For reference, on March 19, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 64%, while on July 26, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 78%.
Cloud Cover Categories in May
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Big Sky, the chance of a wet day over the course of May is rapidly increasing, starting the month at 32% and ending it at 39%.
For reference, the year's highest daily chance of a wet day is 39% on June 1, and its lowest chance is 13% on January 28.
Over the course of May in Big Sky, the chance of a day with only rain increases from 13% to 30%, the chance of a day with mixed snow and rain decreases from 11% to 7%, and the chance of a day with only snow decreases from 8% to 1%.
Probability of Precipitation in May
To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day rainfall during May in Big Sky is rapidly increasing, starting the month at 0.9 inches, when it rarely exceeds 1.5 inches or falls below 0.3 inches, and ending the month at 2.0 inches, when it rarely exceeds 3.4 inches or falls below 0.9 inches.
Average Monthly Rainfall in May
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. As with rainfall, we consider the liquid-equivalent snowfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day liquid-equivalent snowfall during May in Big Sky is gradually decreasing, starting the month at 0.9 inches, when it rarely exceeds 1.7 inches or falls below 0.2 inches, and ending the month at 0.4 inches, when it rarely exceeds 1.0 inches.
Average Monthly Liquid-Equivalent Snowfall in May
Over the course of May in Big Sky, the length of the day is rapidly increasing. From the start to the end of the month, the length of the day increases by 1 hour, 6 minutes, implying an average daily increase of 2 minutes, 12 seconds, and weekly increase of 15 minutes, 27 seconds.
The shortest day of the month is May 1, with 14 hours, 17 minutes of daylight and the longest day is May 31, with 15 hours, 24 minutes of daylight.
Hours of Daylight and Twilight in May
The latest sunrise of the month in Big Sky is 6:14 AM on May 1 and the earliest sunrise is 33 minutes earlier at 5:41 AM on May 31.
The earliest sunset is 8:31 PM on May 1 and the latest sunset is 34 minutes later at 9:05 PM on May 31.
Daylight saving time is observed in Big Sky during 2019, but it neither starts nor ends during May, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 5:37 AM and sets 15 hours, 39 minutes later, at 9:16 PM, while on December 22, the shortest day of the year, it rises at 8:02 AM and sets 8 hours, 44 minutes later, at 4:45 PM.
Sunrise & Sunset with Twilight in May
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
The chance that a given day will be muggy in Big Sky is essentially constant during May, remaining around 0% throughout.
Humidity Comfort Levels in May
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in Big Sky is gradually decreasing during May, decreasing from 5.6 miles per hour to 5.1 miles per hour over the course of the month.
For reference, on January 10, the windiest day of the year, the daily average wind speed is 7.6 miles per hour, while on August 4, the calmest day of the year, the daily average wind speed is 4.5 miles per hour.
Average Wind Speed in May
Wind Direction in May
Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).
The growing season in Big Sky typically lasts for 1.5 months (48 days), from around July 3 to around August 20, rarely starting before June 13, or ending after September 10.
The month of May in Big Sky is reliably fully outside of the growing season.
Time Spent in Various Temperature Bands and the Growing Season in May
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.
The average accumulated growing degree days in Big Sky are gradually increasing during May, increasing by 38°F, from 12°F to 50°F, over the course of the month.
Growing Degree Days in May
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy in Big Sky is gradually increasing during May, rising by 0.8 kWh, from 6.1 kWh to 6.9 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in May
For the purposes of this report, the geographical coordinates of Big Sky are 45.285 deg latitude, -111.368 deg longitude, and 7,772 ft elevation.
The topography within 2 miles of Big Sky contains large variations in elevation, with a maximum elevation change of 2,260 feet and an average elevation above sea level of 7,556 feet. Within 10 miles contains large variations in elevation (5,367 feet). Within 50 miles also contains extreme variations in elevation (7,267 feet).
The area within 2 miles of Big Sky is covered by trees (68%) and shrubs (31%), within 10 miles by trees (60%) and shrubs (30%), and within 50 miles by trees (36%) and shrubs (29%).
This report illustrates the typical weather in Big Sky year round, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 4 weather stations near enough to contribute to our estimation of the temperature and dew point in Big Sky.
For each station, the records are corrected for the elevation difference between that station and Big Sky according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at Big Sky is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Big Sky and a given station.
The stations contributing to this reconstruction are: Gallatin Field Airport (26%, 58 kilometers, north); Dillon Airport (25%, 93 kilometers, west); West Yellowstone (28%, 111 kilometers, southeast); and Bert Mooney Airport (21%, 116 kilometers, northwest).
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.
The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.
We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.
We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.