Polar lows are intense and short-lived cyclones unique to the polar regions. They can have fatal consequences and do great damage. Normally there are between 10 and 20 events in the Atlantic sector during the season from October to April.
Who is affected?
Polar lows typically form over sea in the polar regions, but have been observed as far south as Denmark and the UK. They have a diameter of 100 to 600 km, moving at a speed of 25-50 km / h. The coastal fishing fleet is most vulnerable to the associated strong winds and heavy precipitation, but also land-based activities and aviation in northern Norway may be affected.
The future is uncertain
Forecasting polar lows has traditionally been difficult. The atmosphere is a chaotic system and the ability to predict weather vary with the atmospheric conditions. During unstable weather conditions the forecast uncertainty increases quickly, while in more stable situations the weather can be accurately forecast many days ahead . Many Arctic phenomena are, however, typically unstable.
The current numerical weather prediction models are able to represent with great detail the physical and dynamical processes of the arctic phenomena. Forecasts of polar lows have so far only been based on one single model realization. The latest procurement of a new supercomputer makes it possible to simultaneously run several realizations of these high-resolution forecasts, accounting for the atmospheric uncertainty. Such an ensemble of forecasts provides both the most reliable forecasts and the possibility to calculate the probability of strong winds and heavy precipitation, information that enables users to take action on the basis of their own judgment of risks, costs and damages.
How to forecast - strike probability
By tracking the positions of the forecast polar lows, so-called strike-probability maps are made. The tracking can help to identify polar lows that may otherwise be missed in an analysis of the full atmospheric fields. The strike-probability maps show the likelihood of a polar low occurring at a given location together with its strong winds and heavy precipitation.