September Weather in Anchorage Alaska, United States

Daily high temperatures decrease by 11°F, from 62°F to 50°F, rarely falling below 44°F or exceeding 66°F.

Daily low temperatures decrease by 10°F, from 49°F to 39°F, rarely falling below 30°F or exceeding 53°F.

For reference, on July 19, the hottest day of the year, temperatures in Anchorage typically range from 55°F to 68°F, while on January 17, the coldest day of the year, they range from 13°F to 23°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.

Lena, Norway (3,957 miles away) and Petrozavodsk, Russia (3,939 miles) are the far-away foreign places with temperatures most similar to Anchorage (view comparison).

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The month of September in Anchorage experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 59% throughout the month. The highest chance of overcast or mostly cloudy conditions is 60% on September 18.

The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 41% of the time.

For reference, on December 17, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 63%, while on March 15, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 48%.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Anchorage, the chance of a wet day over the course of September is essentially constant, remaining around 38% throughout.

For reference, the year's highest daily chance of a wet day is 39% on September 26, and its lowest chance is 13% on March 27.

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 Anchorage is gradually decreasing, starting the month at 3.1 inches, when it rarely exceeds 5.0 inches or falls below 1.5 inches, and ending the month at 2.7 inches, when it rarely exceeds 4.8 inches or falls below 1.2 inches.

The highest average 31-day accumulation is 3.1 inches on September 4.

Over the course of September in Anchorage, 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, 44 minutes, implying an average daily decrease of 5 minutes, 40 seconds, and weekly decrease of 39 minutes, 39 seconds.

The shortest day of the month is September 30, with 11 hours, 26 minutes of daylight and the longest day is September 1, with 14 hours, 10 minutes of daylight.

The earliest sunrise of the month in Anchorage is 6:53 AM on September 1 and the latest sunrise is 1 hour, 12 minutes later at 8:05 AM on September 30.

The latest sunset is 9:03 PM on September 1 and the earliest sunset is 1 hour, 32 minutes earlier at 7:31 PM on September 30.

Daylight saving time is observed in Anchorage 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 4:20 AM and sets 19 hours, 23 minutes later, at 11:42 PM, while on December 21, the shortest day of the year, it rises at 10:14 AM and sets 5 hours, 27 minutes later, at 3:41 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 Anchorage is essentially constant during September, remaining around 0% throughout.

For reference, on June 18, 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 Anchorage is gradually increasing during September, increasing from 4.9 miles per hour to 5.7 miles per hour over the course of the month.

For reference, on January 8, the windiest day of the year, the daily average wind speed is 6.6 miles per hour, while on July 5, the calmest day of the year, the daily average wind speed is 4.2 miles per hour.

The highest daily average wind speed during September is 5.7 miles per hour on September 27.

The wind direction in Anchorage during September is predominantly out of the south from September 1 to September 10 and the east from September 10 to September 30.

Anchorage 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 in Anchorage is decreasing during September, falling by 5°F, from 54°F to 49°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 in Anchorage typically lasts for 5.1 months (156 days), from around April 24 to around September 28, rarely starting before April 9 or after May 11, and rarely ending before September 10 or after October 14.

During September in Anchorage, the chance that a given day is within the growing season is very rapidly decreasing falling from 98% to 44% 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 Anchorage are gradually increasing during September, increasing by 74°F, from 896°F to 970°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 Anchorage is decreasing during September, falling by 1.4 kWh, from 3.3 kWh to 1.9 kWh, over the course of the month.

For the purposes of this report, the geographical coordinates of Anchorage are 61.218 deg latitude, -149.900 deg longitude, and 98 ft elevation.

The topography within 2 miles of Anchorage contains only modest variations in elevation, with a maximum elevation change of 177 feet and an average elevation above sea level of 48 feet. Within 10 miles contains only modest variations in elevation (3,212 feet). Within 50 miles contains large variations in elevation (7,936 feet).

The area within 2 miles of Anchorage is covered by artificial surfaces (79%) and sparse vegetation (14%), within 10 miles by water (29%) and trees (22%), and within 50 miles by trees (32%) and shrubs (21%).