This report describes the typical weather at the Allen Army Airfield (Big Delta Army Airfield) (Fort Greely/Delta Junction, Alaska, United States) weather station over the course of an average year. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
Fort Greely/Delta Junction, Alaska has a continental climate with dry winters and short cool summers. The area within 25 mi of this station is covered by forests (78%), tundra (20%), and lakes and rivers (3%).
Over the course of a year, the temperature typically varies from -8°F to 69°F and is rarely below -35°F or above 78°F.
The warm season lasts from May 13 to September 10 with an average daily high temperature above 56°F. The hottest day of the year is July 9, with an average high of 69°F and low of 52°F.
The cold season lasts from November 4 to February 29 with an average daily high temperature below 17°F. The coldest day of the year is January 5, with an average low of -8°F and high of 4°F.
The length of the day varies significantly over the course of the year. The shortest day is December 21 with 4:13 hours of daylight; the longest day is June 20 with 21:00 hours of daylight.
The earliest sunrise is at 3:14am on June 16 and the latest sunset is at 12:16am on June 24. The latest sunrise is at 10:36am on December 24 and the earliest sunset is at 2:46pm on December 17.
Daylight saving time (DST) is observed in this location during 2012, starting in the spring on March 11 and ending in the fall on November 4.
The median cloud cover ranges from 55% (partly cloudy) to 84% (mostly cloudy). The sky is cloudiest on July 27 and clearest on March 12. The clearer part of the year begins around December 5. The cloudier part of the year begins around May 2.
On March 12, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 38% of the time, and overcast or mostly cloudy 38% of the time.
On July 27, the cloudiest day of the year, the sky is overcast, mostly cloudy, or partly cloudy 66% of the time, and clear or mostly clear 11% of the time.
The probability that precipitation will be observed at this location varies throughout the year. Precipitation is most likely around July 14, occurring in 45% of days. Precipitation is least likely around March 30, occurring in 25% of days.
Over the entire year, the most common forms of precipitation are light snow and light rain.
Light snow is the most severe precipitation observed during 51% of those days with precipitation. It is most likely around November 6, when it is observed during 38% of all days.
Light rain is the most severe precipitation observed during 31% of those days with precipitation. It is most likely around August 3, when it is observed during 31% of all days.
During the warm season, which lasts from May 13 to September 10, there is a 41% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of light rain (67% of days with precipitation have at worst light rain), moderate rain (15%), and thunderstorms (10%).
During the cold season, which lasts from November 4 to February 29, there is a 37% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of light snow (89% of days with precipitation have at worst light snow) and moderate snow (8%).
The likelihood of snow falling is highest around November 6, occurring in 42% of days. The season in which it is relatively likely for snow to fall spans from September 16 to April 29.
Either snow rarely accumulates at this location or snow depth measurements are unavailable or unreliable.
The relative humidity typically ranges from 31% (comfortable) to 90% (very humid) over the course of the year, rarely dropping below 18% (dry) and reaching as high as 100% (very humid).
The air is driest around May 16, at which time the relative humidity drops below 37% (comfortable) three days out of four; it is most humid around October 18, exceeding 86% (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 year, the dew point typically varies from -15°F (dry) to 51°F (very comfortable) and is rarely below -39°F (dry) or above 56°F (comfortable).
The time of the year between July 6 and July 31 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of the year typical wind speeds vary from 0 mph to 22 mph (calm to fresh breeze), rarely exceeding 35 mph (high wind).
The highest average wind speed of 12 mph (moderate breeze) occurs around January 18, at which time the average daily maximum wind speed is 22 mph (fresh breeze).
The lowest average wind speed of 6 mph (light breeze) occurs around July 10, at which time the average daily maximum wind speed is 11 mph (gentle breeze).