Winds: the sea breeze and the 'halny'
The main pressure systems that affect the weather are the Icelandic low (stronger in winter) and the Azores anticyclone (more active in summer) as well as the changing atmospheric fronts from Asia: the East Asian high in winter and the South Asian low in summer. For a major part of the year Poland has predominantly west circulation of winds, caused by the eastward movement of barometric lows from the Atlantic. As a result, on 60 percent of all windy days the winds are from the west, blowing mainly from the area stretching between the Czech Republic and Scandinavia. In the eastern part of the country, the percentage of easterly winds is higher, while in the mountains, southerly winds occur more frequently.
The wind pattern is not uniform throughout the year. In summer months, that is from July to September, the winds are mainly westerly, whereas in winter, notably in December and January, easterly winds prevail. In the transitory seasons, both winds occur roughly with the same frequency.
The winds in Poland are typically weak to moderate, their speed ranging from 2 to 10 m/s. Strong and very strong winds occur at the seaside, causing storms, and in the mountains, where their speed may exceed 30 m/s. Hurricanes that uproot trees and blow off roofs are rather unusual.
With its diversified topography, Poland also has local winds. Along the Baltic coast, on a cloudless summer day you can experience a pleasant, invigorating sea breeze which occurs during the day and is felt about 10km inland. At night its direction reverses: the air moves from the cooler land towards the warmer sea, causing the land breeze.
In the mountains, there are mountain-valley winds. The best-known one is the halny, which blows in the Tatras and has been the subject of many poems and paintings. This kind of wind is not unique to Poland, though; it occurs in all mountains around the world and is called the föhn.
The halny is strong and gusty and its effects are higher temperature and lower air humidity on the leeward slopes. It develops when moving air is stopped by a mountain range and forced to rise. The halny is a nuisance for people as it lowers their mental and physical fitness and makes them irritable. It is strong enough to break trees, sometimes over large areas, blow off roofs and knock over fences. In winter it causes sudden thaws leading to floods.
