September Weather in Shenandoah National Park United States

Daily high temperatures decrease by 10°F, from 83°F to 73°F, rarely falling below 63°F or exceeding 91°F.

Daily low temperatures decrease by 10°F, from 61°F to 51°F, rarely falling below 38°F or exceeding 69°F.

For reference, on July 20, the hottest day of the year, temperatures in Shenandoah National Park typically range from 66°F to 87°F, while on January 30, the coldest day of the year, they range from 25°F to 45°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.

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The month of September in Shenandoah National Park experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 35% throughout the month. The lowest chance of overcast or mostly cloudy conditions is 34% on September 22.

The clearest day of the month is September 22, with clear, mostly clear, or partly cloudy conditions 66% of the time.

For reference, on December 23, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 52%, while on September 22, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 66%.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Shenandoah National Park, the chance of a wet day over the course of September is decreasing, starting the month at 28% and ending it at 23%.

For reference, the year's highest daily chance of a wet day is 41% on July 13, and its lowest chance is 19% on October 19.

Rainfall

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 September in Shenandoah National Park is essentially constant, remaining about 3.2 inches throughout, and rarely exceeding 7.1 inches or falling below 0.8 inches.

The highest average 31-day accumulation is 3.2 inches on September 26.

Over the course of September in Shenandoah 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, 11 minutes, implying an average daily decrease of 2 minutes, 27 seconds, and weekly decrease of 17 minutes, 10 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 Shenandoah National Park is 6:43 AM on September 1 and the latest sunrise is 26 minutes later at 7:09 AM on September 30.

The latest sunset is 7:42 PM on September 1 and the earliest sunset is 46 minutes earlier at 6:57 PM on September 30.

Daylight saving time is observed in Shenandoah National Park during 2024, but it neither starts nor ends during September, so the entire month is in standard time.

For reference, on June 20, the longest day of the year, the Sun rises at 5:49 AM and sets 14 hours, 51 minutes later, at 8:41 PM, while on December 21, the shortest day of the year, it rises at 7:27 AM and sets 9 hours, 29 minutes later, at 4:56 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 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.

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 Shenandoah National Park is very rapidly decreasing during September, falling from 38% to 10% over the course of the month.

For reference, on July 23, the muggiest day of the year, there are muggy conditions 63% of the time, while on January 24, 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 Shenandoah National Park is gradually increasing during September, increasing from 4.0 miles per hour to 4.6 miles per hour over the course of the month.

For reference, on February 26, the windiest day of the year, the daily average wind speed is 6.6 miles per hour, while on August 12, the calmest day of the year, the daily average wind speed is 3.8 miles per hour.

The hourly average wind direction in Shenandoah National Park throughout September is predominantly from the west, with a peak proportion of 33% on September 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 Shenandoah National Park typically lasts for 6.2 months (189 days), from around April 13 to around October 19, rarely starting before March 27 or after May 2, and rarely ending before September 30 or after November 6.

The month of September in Shenandoah National Park is more likely than not fully within the growing season, with the chance that a given day is in the growing season decreasing from 100% to 89% 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 Shenandoah National Park are rapidly increasing during September, increasing by 499°F, from 3,060°F to 3,559°F, over the course of the month.

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 Shenandoah National Park is decreasing during September, falling by 1.2 kWh, from 5.8 kWh to 4.6 kWh, over the course of the month.

For the purposes of this report, the geographical coordinates of Shenandoah National Park are 38.492 deg latitude, -78.469 deg longitude, and 0 ft elevation.

The topography within 2 miles of Shenandoah 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 Shenandoah National Park is covered by trees (100%), within 10 miles by trees (76%) and cropland (24%), and within 50 miles by trees (69%) and cropland (29%).