weather lacks Rossby waves are part of the planetary circulation and are large-scale wave movements in the atmosphere in the mid-latitudes, including here in Switzerland. They meande and separate the warm subtropical air in the south from the cold polar air in the north. The large-scale waves determine our weather in the westerly wind zone. If the Rossby wave swings northwards, ie the upper air current arches up a ridge, we are in a high pressure area under and just before the ridge. If the Rossby wave swings southwardsnd – in the direction of flow – immediately in front of the trough there is a low pressure influence and thus unstable weather. The decisive factor for the weather character is therefore which side of the Rossby wave you are on.
The number of waves determines the weather pattern
The Rossby waves at altitude control the position of the high and low pressure areas on the ground and thus our weather. The following applies: the more Rossby waves simultaneously spanning a hemisphere, in our case the northern hemisphere, the faster they move eastwards. Many smaller Rossby waves therefore ensure a rapid change between high and low pressure areas in a region and thus constantly changing weather. If the number of waves drops below 5, however, the large Rossby waves, which often meander far north and south, remain stationary or even move backwards to the west.
October weather so far
In the last two weeks of October, the Rossby waves in the northern hemisphere were fairly stationary for a long time (see above). For most of the time, Switzerland was located exactly between a trough (low pressure area) over Western Europe and a ridge (high pressure area) over Eastern Europe. This resulted in a very mild, but at times humid, southwesterly flow over the Alpine region. It brought dense cloud fields and repeated precipitation not only to the create a site with the ai assistant that comes to sitebuilder pro areas of the southern side of the Alps, but also north of the Alps. On most days, the high was too far away in the east for classic Indian summer weather. Accordingly, the monthly sunshine duration is currently below average, regardless of the fog at all altitudes.
In mid-September and early October, the Rossby waves were exactly out of phase and a trough was located over large parts of Central Europe. This was also the reason for the early onset of cold air in September and the cold start to October. The last 14 days, however, were clearly too warm for the time of year with the very mild southwesterly flow and despite the mixed weather.