Coastal regions of Otago are subject to the alternating warm and dry/cool and wet weather patterns common to the interannual Southern oscillation. The Southern Hemisphere storm track produces an irregular short cycle of weather which repeats roughly every week, with three or four days of fine weather followed by three or four days of cooler, damp conditions. Drier conditions are often the result of the northwesterly föhn wind, which dries as it crosses the Southern Alps. Wetter air is the result of approaching low-pressure systems which sweep fronts over the country from the southwest. A common variant in this pattern is the centring of a stationary low-pressure zone to the southeast of the country, resulting in long-lasting cool, wet conditions. These have been responsible for several notable historical floods, such as the "hundred year floods" of October 1878 and October 1978.