According to Wikipedia, orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it quickly cools down adiabatically (its pressure and temperature both decrease without the gain or loss of heat), which can raise the relative humidity to 100%. Precipitation can then occur from this orographic effect. Here's the weather bureau's summary for the month (lightly edited for brevity):
National Weather Service's monthly weather summary for August 2015 for Fairbanks, Alaska
August 2015 was the third consecutive month of below normal temperatures for Fairbanks. The warmest temperature of the month occurred on the 4th when the temperature soared to 80 degrees; this was the 11th 80 degree or warmer day of the summer.
An unseasonably cold low pressure system brought heavy rain to much of the interior and boosted the monthly rainfall to 2.58 inches...which was 0.70 inches above the normal of 1.88 inches.
The average high temperature was 62.0 degrees, which was 3.9 degrees below the normal high of 65.9 degrees. The average low temperature was 47.1 degrees...which was 0.7 degrees above the normal low temperature of 46.4 degrees.
The average temperature for the month was 54.6 degrees, which was 1.5 degrees below the average temperature of 56.1 degrees and ranks as the 37th coldest of 109 years of record.
A very fall like storm moved into the interior on the 25th and 26th and ushered in unseasonably cold temperatures that continued through the end of the month. Although snow was not reported at Fairbanks there were reports of snow in the hills north and east of town.
A frost advisory was issued for the morning of the 31st with the temperature at the airport dropping to 33 degrees, that was the coldest temperature recorded during the month. Many of the local cold spots in the area dropped into the upper 20s and lower 30s.
Looking forward to September...possible sunshine continues to decrease by 6 and a half minutes per day with day light hours decreasing from 14 hours and 38 minutes on the 1st to 11 hours and 25 minutes on the 30th. The average daily high temperature decreases from 60.5 degrees on the 1st to 46.2 degrees on the 30th. The average daily low temperature decreases from 41.3 degrees on the 1st to 30.1 degrees on the 30th. The average rainfall is 1.1 inches and the average snowfall is 1.8 inches.
Source: NWS, Fairbanks Forecast Office, 9/2/15.