September Weather in Arches National Park Utah, United StatesDaily high temperatures decrease by 11°F, from 88°F to 77°F, rarely falling below 65°F or exceeding 94°F. Daily low temperatures decrease by 11°F, from 62°F to 51°F, rarely falling below 42°F or exceeding 68°F. For reference, on July 7, the hottest day of the year, temperatures in Arches National Park typically range from 68°F to 95°F, while on January 4, the coldest day of the year, they range from 20°F to 38°F. The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on September. 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. CloudsThe month of September in Arches National Park experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 22% throughout the month. The lowest chance of overcast or mostly cloudy conditions is 20% on September 18. The clearest day of the month is September 18, with clear, mostly clear, or partly cloudy conditions 80% of the time. For reference, on March 2, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 45%, while on September 18, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 80%. PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Arches National Park, the chance of a wet day over the course of September is essentially constant, remaining around 17% throughout. For reference, the year's highest daily chance of a wet day is 18% on July 31, and its lowest chance is 5% on June 13. RainfallTo 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 September in Arches National Park is essentially constant, remaining about 1.0 inches throughout, and rarely exceeding 2.1 inches or falling below 0.2 inches. SunOver the course of September in Arches National Park, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1 hour, 12 minutes, implying an average daily decrease of 2 minutes, 28 seconds, and weekly decrease of 17 minutes, 19 seconds. The shortest day of the month is September 30, with 11 hours, 48 minutes of daylight and the longest day is September 1, with 12 hours, 59 minutes of daylight. The earliest sunrise of the month in Arches National Park is 6:48 AM on September 1 and the latest sunrise is 26 minutes later at 7:13 AM on September 30. The latest sunset is 7:47 PM on September 1 and the earliest sunset is 46 minutes earlier at 7:01 PM on September 30. Daylight saving time is observed in Arches National Park during 2024, but it neither starts nor ends during September, so the entire month is in daylight saving time. For reference, on June 20, the longest day of the year, the Sun rises at 5:53 AM and sets 14 hours, 53 minutes later, at 8:46 PM, while on December 21, the shortest day of the year, it rises at 7:33 AM and sets 9 hours, 27 minutes later, at 5:00 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. MoonThe figure below presents a compact representation of key lunar data for September 2024. 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.
HumidityWe 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 Arches National Park is essentially constant during September, remaining around 0% throughout. For reference, on July 30, 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. WindThis 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 Arches National Park is essentially constant during September, remaining within 0.2 miles per hour of 6.9 miles per hour throughout. For reference, on April 10, the windiest day of the year, the daily average wind speed is 8.8 miles per hour, while on January 7, the calmest day of the year, the daily average wind speed is 6.1 miles per hour. The highest daily average wind speed during September is 7.1 miles per hour on September 27. The hourly average wind direction in Arches National Park throughout September is predominantly from the south, with a peak proportion of 48% on September 1. Growing SeasonDefinitions 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 Arches National Park typically lasts for 6.5 months (201 days), from around April 11 to around October 28, rarely starting before March 19 or after May 1, and rarely ending before October 10 or after November 14. The month of September in Arches National Park is very likely fully within the growing season, with the chance that a given day is in the growing season gradually decreasing from 100% to 97% over the course of the month. 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 Arches National Park are rapidly increasing during September, increasing by 544°F, from 3,312°F to 3,856°F, over the course of the month. Solar EnergyThis 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 Arches National Park is decreasing during September, falling by 1.0 kWh, from 6.4 kWh to 5.3 kWh, over the course of the month. TopographyFor the purposes of this report, the geographical coordinates of Arches National Park are 38.723 deg latitude, -109.586 deg longitude, and 4,022 ft elevation. The topography within 2 miles of Arches National Park contains significant variations in elevation, with a maximum elevation change of 771 feet and an average elevation above sea level of 4,808 feet. Within 10 miles contains significant variations in elevation (2,149 feet). Within 50 miles contains large variations in elevation (8,921 feet). The area within 2 miles of Arches National Park is covered by shrubs (100%), within 10 miles by shrubs (99%), and within 50 miles by shrubs (82%) and trees (10%). Data SourcesThis report illustrates the typical weather in Arches National Park, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016. The details of the data sources used for this report can be found on the Moab page. DisclaimerThe 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. 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