Winter weather in the North and Norwegian Seas is dominated by strong low-pressure activity in the Atlantic, with depressions following a north-easterly course. These are usually strongest around Iceland and lose much of their intensity before reaching the Barents Sea. So the far north of the NCS has less wind on average than further south.
Wave conditions largely relate directly to wind forces, but deep and slow-moving depressions can also create high seas in Arctic waters.
Although the big Atlantic depressions do not bring as much wind and waves as in the south, variable conditions with gales and storms can quickly arise.
Polar lows occur when cold air from the ice cap blows across warm seawater and rises. More cold air is drawn in, creating a small but intense depression about 100-500 kilometres across.
Rapid changes are characteristic. Wind strength can rise from breeze to storm in minutes, while wave heights have been seen to increase up to five metres in less than an hour. Thick snow and poor visibility are also usual, and can lead to heavy icing. The actual depressions also move fast, with speeds of about 15-25 knots. Polar lows often disappear as quickly as they arise, and seldom last more than 18 hours on average.
A trough can resemble a Polar low, but consists in reality of thick snow clouds which produce very poor visibility. It forms as the Gulf Stream carries warm water north.
Big temperature differences between sea and air produce “seething” air conditions with much precipitation and thick clouds. Onshore storm winds and thunder often accompany a trough.
The common denominator of Polar lows and troughs is their unpredictability. To provide detailed and reliable forecasts, meteorologists need a lot of data.
Unfortunately, both weather measurements and observations are in short supply on the NCS. These weather phenomena are also relatively small scale, and not easy to detect with existing forecasting models. Satellites and weather radar can be used to predict the course of the weather once it has arisen. Polar lows can be tracked by satellite, since they have a recognisable rotational form. But troughs can be hidden because the Earth’s curvature causes radar beams to overshoot the low-lying snow clouds. The further they are from land, the harder radar detection becomes.
Temperature conditions are reversed during the summer, with the sea colder than the air. When the air flows over the sea, it cools and its relative humidity rises. Fogs occur once the air is saturated with moisture.
The temperature contrasts increase around Bear Island, where very foggy conditions can arise as warm air from the land seeps out over the sea and cools. As a result, visibility of less than a kilometre is experienced on an average of 76 days per year in these waters.