This report describes the typical weather at the Fairbanks International Airport (Fairbanks, Alaska, United States) weather station over the course of an average September. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
Fairbanks, Alaska has a humid subarctic continental climate with cool summers and no dry season. The area within 25 mi of this station is covered by forests (96%) and lakes and rivers (3%).
The month of September is characterized by very rapidly falling daily high temperatures, with daily highs decreasing from 61°F to 45°F over the course of the month, exceeding 70°F or dropping below 35°F only one day in ten.
Over the course of September, 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 3:14 hours, implying an average day-over-day decrease of 6.5 minutes.
The shortest day of the month is September 30 with 11:20 hours of daylight; the longest day is September 1 with 14:35 hours of daylight.
The earliest sunrise is at 6:33am on September 1; the latest sunset is at 9:07pm on September 1; the latest sunrise is at 8:01am on September 30; the earliest sunset is at 7:21pm on September 30.
Daylight savings time is observed in 2012 but it neither starts nor ends in September, so the entire month is in daylight time.
The median cloud cover is 92% (mostly cloudy) and does not vary substantially over the course of the month.
On September 15, a representative day, the sky is clear or mostly clear 19% of the time, partly cloudy 16% of the time, and mostly cloudy or overcast 65% of the time.
The average probability that some form of precipitation will be observed in a given day is 53%, with little variation over the course of the month.
Throughout September, the most common forms of precipitation are light rain, light snow, and moderate rain.
Light rain is the most severe precipitation observed during 48% of those days with precipitation. It is most likely around September 1, when it is observed during 32% of all days.
Light snow is the most severe precipitation observed during 26% of those days with precipitation. It is most likely around September 30, when it is observed during 24% of all days.
Moderate rain is the most severe precipitation observed during 17% of those days with precipitation. It is most likely around September 1, when it is observed during 13% of all days.
The likelihood of snow falling is highest around September 30, occurring in 30% of days.
Accumulation at this location in September is unlikely. The chances of there being snow on the ground are highest around September 30, occurring 13% of the time.
The snow is typically at its deepest on September 15, with a median depth of 6.4"; the depth exceeds 7.7" only one year out of ten.
The relative humidity typically ranges from 48% (comfortable) to 92% (very humid) over the course of a typical September, rarely dropping below 32% (comfortable) and reaching as high as 99% (very humid).
The air is driest around September 1, at which time the relative humidity drops below 57% (mildly humid) three days out of four; it is most humid around September 3, rising above 89% (very humid) three days out of four.
Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
Over the course of a typical September, the dew point typically varies from 24°F (dry) to 46°F (dry) and is rarely below 15°F (dry) or above 52°F (very comfortable).
Over the course of September typical wind speeds vary from 0 mph to 11 mph (calm to gentle breeze), rarely exceeding 17 mph (moderate breeze).
The highest average wind speed of 6 mph (light breeze) occurs around September 26, at which time the average daily maximum wind speed is 11 mph (gentle breeze).
The lowest average wind speed of 5 mph (light breeze) occurs around September 5, at which time the average daily maximum wind speed is 10 mph (gentle breeze).