Fall Weather in Zion National Park Utah, United States

Daily high temperatures decrease by 37°F, from 92°F to 54°F, rarely falling below 44°F or exceeding 98°F.

Daily low temperatures decrease by 31°F, from 64°F to 33°F, rarely falling below 24°F or exceeding 70°F.

For reference, on July 12, the hottest day of the year, temperatures in Zion National Park typically range from 69°F to 98°F, while on January 5, the coldest day of the year, they range from 28°F to 49°F.

The figure below shows you a compact characterization of the hourly average fall temperatures. 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.

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The fall in Zion National Park experiences very rapidly increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 19% to 37%. The lowest chance of overcast or mostly cloudy conditions is 15% on September 20.

The clearest day of the fall is September 20, with clear, mostly clear, or partly cloudy conditions 85% of the time.

For reference, on February 13, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 44%, while on September 20, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 85%.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Zion National Park, the chance of a wet day over the course of the fall is rapidly decreasing, starting the season at 15% and ending it at 8%.

For reference, the year's highest daily chance of a wet day is 18% on August 11, and its lowest chance is 4% on June 19.

Rainfall

To show variation within the season and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during the fall in Zion National Park is essentially constant, remaining about 0.8 inches throughout, and rarely exceeding 2.0 inches.

The lowest average 31-day accumulation is 0.7 inches on November 28.

Over the course of the fall in Zion National Park, the length of the day is very rapidly decreasing. From the start to the end of the season, the length of the day decreases by 3 hours, 10 minutes, implying an average daily decrease of 2 minutes, 7 seconds, and weekly decrease of 14 minutes, 47 seconds.

The shortest day of the fall is November 30, with 9 hours, 48 minutes of daylight and the longest day is September 1, with 12 hours, 58 minutes of daylight.

The latest sunrise of the fall in Zion National Park is 7:59 AM on November 4 and the earliest sunrise is 59 minutes earlier at 7:00 AM on November 5.

The latest sunset is 8:01 PM on September 1 and the earliest sunset is 2 hours, 46 minutes earlier at 5:14 PM on November 30.

Daylight saving time (DST) ends at 1:00 AM on November 5, 2023, shifting sunrise and sunset to be an hour earlier.

For reference, on June 21, the longest day of the year, the Sun rises at 6:11 AM and sets 14 hours, 44 minutes later, at 8:55 PM, while on December 22, the shortest day of the year, it rises at 7:42 AM and sets 9 hours, 36 minutes later, at 5:18 PM.

The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.

The figure below presents a compact representation of key lunar data for the fall of 2023. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.

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 Zion National Park is essentially constant during the fall, remaining around 0% throughout.

For reference, on July 24, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, the least muggy day of the year, there are muggy conditions 0% of the time.

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 Zion National Park is gradually increasing during the fall, increasing from 6.7 miles per hour to 7.7 miles per hour over the course of the season.

For reference, on April 11, the windiest day of the year, the daily average wind speed is 9.1 miles per hour, while on August 3, the calmest day of the year, the daily average wind speed is 6.4 miles per hour.

The wind direction in Zion National Park during the fall is predominantly out of the south from September 1 to October 3 and the east from October 3 to November 30.

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 Zion National Park typically lasts for 7.4 months (226 days), from around March 28 to around November 9, rarely starting before March 2 or after April 18, and rarely ending before October 21 or after November 27.

During the fall in Zion National Park, the chance that a given day is within the growing season is very rapidly decreasing falling from 100% to 7% over the course of the season.

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 Zion National Park are very rapidly increasing during the fall, increasing by 1,080°F, from 3,586°F to 4,666°F, over the course of the season.

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 Zion National Park is very rapidly decreasing during the fall, falling by 3.5 kWh, from 6.6 kWh to 3.0 kWh, over the course of the season.

For the purposes of this report, the geographical coordinates of Zion National Park are 37.298 deg latitude, -113.026 deg longitude, and 0 ft elevation.

The topography within 2 miles of Zion National Park is essentially flat, with a maximum elevation change of 0 feet and an average elevation above sea level of 0 feet. Within 10 miles is also essentially flat (0 feet). Within 50 miles is also essentially flat (0 feet).

The area within 2 miles of Zion National Park is covered by shrubs (85%) and grassland (11%), within 10 miles by shrubs (68%) and trees (28%), and within 50 miles by shrubs (76%) and trees (19%).