Winter Pressure Systems and Ice Fog in Fairbanks, Alaska

Abstract

The production of the low temperatures which are responsible for ice fog in inhabited areas of interior Alaska would appear to be a classic example of clear sky radiative cooling under nearly polar night conditions. However, examination of the meteorological conditions associated with 15 periods of dense ice fog at Fairbanks indicates that local radiative cooling is important only in producing the observed steep ground inversion. The most rapid decreases in temperature at heights >1 km occurred with cloud cover and cold air advection preceding the cold weather at the ground. The most common synoptic pattern (observed for the 12 shortest events) consisted of the migration of a small high from Siberia across Alaska. Rapid growth of the high was common, and the resulting subsidence was strong enough to counterbalance not only radiative cooling, but further cold air advection as well. This resulted in an observed warming aloft during all but the first 12?24 hr of the clear, cold weather observed at the ground. Three of the 15 events did not follow this pattern. Two long and very cold events were associated with warm highs in northeastern Siberia, continuous belts of moderately high pressure extending from Siberia across the Bering Strait into Alaska, and advection from Siberia and the Arctic Ocean. The remaining long but relatively mild event was associated with a warm high north of Alaska and advection from Canada and the Arctic Ocean.