Two forms of block high pressure systems
In the westerly currents that prevail in our mid-latitudes, it sometimes! happens that the upper airflow curves northward more than usual. In such a situation, the jet stream configuration tends to “freeze” and stay in place, rather than forming waves along! its flow that then shift from west to east.
“Omega blocks” are nam because of their pattern! which resembles the Greek capital letter Omega (Ω). The blocking high pressure area is usually! flank by a low pressure area to the east and a second low! pressure area to the west. The high pressure axis often runs north-south, but it can also be tilt to the side.
A split in the easterly flow at the southern ge of the high can also lead to a “diffluent block” (see right graphic below). Flow patterns with a clos high in the north and a clos low in the south often last for a longer period of time.
Schematic representation of a blocking high pressure
ituation «Omega situation» (left) and a «diffluent block» (right) over northwestern Europe.
>Schematic representation of a blocking high pressure saudi arabia phone number library system “Omega position” (left) and a “diffluent block” (right) over northwestern Europe.
It is usually somewhat less active than the flanking lows in the “Omega Block”.
self-preservation of the stable configuration
Another characteristic of “omega blocks” and “diffluent blocks” is that they tend to be self-perpetuating. The central ridge is usually continuously suppli with warm air from the southwest sector at the front of the upstream low. This warm air advection strengthens the high pressure ridge. The opposite occurs with the flanking lows on either side of an “omega block”. They receive cold polar air from a persistent flow from the north. This cold air advection also strengthens the low pressure areas. This largely explains the longevity of these so-call “blocking” configurations.
The flow situation at 500 hPa with geopotential and air temperature on February 6, 2023, 12Z. A self-preservation mechanism works in blocking situations in which warm air (r arrow) supplies the high and cold air (blue arrows) supplies the lows.
The flow situation at 500 hPa with geopotential and selling as a team air temperature on February 6, 2023, 12Z. A self-preservation mechanism works in blocking situations in which warm air (r arrow) supplies the high and cold air (blue arrows) supplies the lows. (Source: MeteoSwiss / ECMWF)
forecast for the coming week
Over the next few days, the strong high already over the nearby Atlantic will slowly shift to Central Europe. On Sunday (5 February) and Monday (6 February), an Omega situation will form over southern England and the North Sea with the axis of the high tilt to the southwest-northeast. Until then, we will still be concern with two cold air germany cell number drops that will move over the Alpine region on the eastern flank of the high.