In recent days, a so-called omega situation has set in. This is characterized by a great consistency and longevity. But what exactly is an omega situation and how long does it last? More about this below.
Current omega high or blocking high
Sun, sun and above all in the height exceptionally high temperatures. This is how the weather report reads since a few days. The reason for the current good weather phase is a so-called omega high. In this large-scale weather situation, a stable high-pressure area is flanked by two low-pressure areas. The resulting pressure formation is reminiscent of the Greek letter omega , hence its name. Such a weather situation is extremely stable and can therefore last for several days or even weeks. At the moment, the high pressure area is located over Central Europe and the lows over the Atlantic and the eastern Mediterranean (see Fig. 1).
Fig. 1: Weather situation today Tuesday: Omega-shaped high over Central Europe (European weather model ECMWF); Source: MeteoNews, UBIMET
As long as the low pressure area over the Atlantic does not lose intensity, it supports the high pressure area with warm air advection on its front. Thus, the weather situation often regenerates itself and can remain in equilibrium for several days to weeks (typically 4 to 10 days). In this process, the Atlantic low pressure areas are guided around Central Europe, so that the westward drift is blocked. Depending on the location of these areas, there are both longer dry periods and warmth or in winter cold (in the high), but on the other hand also longer wet and cool weather periods (within the flanking lows). In the area of the two low pressure areas, however, the omegas – in summer and winter – always leads to heavy precipitation and storms. While it is currently sunny and exceptionally warm in central Europe, the eastern flanking low in Greece is currently leading to extremely large rainfall amounts with a high risk of flooding (more about this tomorrow, see Figs. 2 and 3).
Fig. 2: What a contrast: Weather currently in Zurich...; Source: roundshot
Fig. 3: ... and in Sparta (Greece); Source: skyline webcams
Omega layers are stable, but not completely stationary. As a result, a long period of good weather can be followed by a long period of bad weather, and vice versa, if the pressure formations shift.
When does it end?
The omega situation and with it the sunny and late summer warm weather in our region will last all week and will continue into the coming week. In the first half of next week, however, the high pressure will slowly shift to the northeast, so that towards the middle of next week Atlantic lows in Central Europe should gain some influence. However, the exact weather pattern is still unclear, it could also be that we stay connected to the high until well past the middle of next week.
Examples of previous omegas
There are many examples of past omegas. One of the most famous might be the 2003 heat summer triggered by an omega high named Michaela. An omega high was also responsible for the sun-drenched World Cup in Germany in June 2006. In English-speaking countries, this is also referred to as a heat dome. This summer, for example, such a heat dome led to new absolute heat records in places in the U.S. states of Nevada, Arizona and California.