September Weather at Juneau International Airport United States

Daily high temperatures decrease by 8°F, from 59°F to 51°F, rarely falling below 47°F or exceeding 66°F.

Daily low temperatures decrease by 5°F, from 48°F to 43°F, rarely falling below 34°F or exceeding 52°F.

For reference, on July 29, the hottest day of the year, temperatures at Juneau International Airport typically range from 51°F to 65°F, while on December 30, the coldest day of the year, they range from 25°F to 32°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.

Trondheim, Norway (3,825 miles away) is the far-away foreign place with temperatures most similar to Juneau International Airport (view comparison).

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The month of September at Juneau International Airport experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 74% to 79%.

The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 26% of the time.

For reference, on October 4, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 81%, while on May 25, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 32%.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. At Juneau International Airport, the chance of a wet day over the course of September is rapidly increasing, starting the month at 64% and ending it at 70%.

For reference, the year's highest daily chance of a wet day is 74% on October 9, and its lowest chance is 42% on May 26.

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 at Juneau International Airport is very rapidly increasing, starting the month at 11.3 inches, when it rarely exceeds 16.3 inches or falls below 6.0 inches, and ending the month at 15.0 inches, when it rarely exceeds 19.7 inches or falls below 10.6 inches.

Over the course of September at Juneau International Airport, the length of the day is very rapidly decreasing. From the start to the end of the month, the length of the day decreases by 2 hours, 26 minutes, implying an average daily decrease of 5 minutes, 2 seconds, and weekly decrease of 35 minutes, 16 seconds.

The shortest day of the month is September 30, with 11 hours, 30 minutes of daylight and the longest day is September 1, with 13 hours, 57 minutes of daylight.

The earliest sunrise of the month at Juneau International Airport is 5:59 AM on September 1 and the latest sunrise is 1 hour, 3 minutes later at 7:02 AM on September 30.

The latest sunset is 7:55 PM on September 1 and the earliest sunset is 1 hour, 23 minutes earlier at 6:32 PM on September 30.

Daylight saving time is observed at Juneau International Airport 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 3:51 AM and sets 18 hours, 18 minutes later, at 10:08 PM, while on December 21, the shortest day of the year, it rises at 8:46 AM and sets 6 hours, 22 minutes later, at 3:07 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 at Juneau International Airport is essentially constant during September, remaining around 0% throughout.

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 at Juneau International Airport is increasing during September, increasing from 5.9 miles per hour to 7.4 miles per hour over the course of the month.

For reference, on January 1, the windiest day of the year, the daily average wind speed is 10.9 miles per hour, while on July 3, the calmest day of the year, the daily average wind speed is 4.7 miles per hour.

The hourly average wind direction at Juneau International Airport throughout September is predominantly from the south, with a peak proportion of 45% on September 16.

Juneau International Airport is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average surface water temperature at Juneau International Airport is gradually decreasing during September, falling by 3°F, from 54°F to 51°F, over the course of the month.

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 at Juneau International Airport typically lasts for 5.3 months (161 days), from around April 30 to around October 8, rarely starting before April 11 or after May 20, and rarely ending before September 18 or after October 31.

The month of September at Juneau International Airport is more likely than not fully within the growing season, with the chance that a given day is in the growing season rapidly decreasing from 99% to 69% 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 at Juneau International Airport are gradually increasing during September, increasing by 54°F, from 626°F to 679°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 at Juneau International Airport is decreasing during September, falling by 1.3 kWh, from 2.8 kWh to 1.6 kWh, over the course of the month.

For the purposes of this report, the geographical coordinates of Juneau International Airport are 58.355 deg latitude, -134.576 deg longitude, and 13 ft elevation.

The topography within 2 miles of Juneau International Airport contains very significant variations in elevation, with a maximum elevation change of 1,765 feet and an average elevation above sea level of 133 feet. Within 10 miles contains very significant variations in elevation (5,820 feet). Within 50 miles also contains extreme variations in elevation (8,451 feet).

The area within 2 miles of Juneau International Airport is covered by trees (30%), sparse vegetation (29%), and water (21%), within 10 miles by trees (35%) and water (26%), and within 50 miles by trees (28%) and water (24%).