Weather Insider: Blocking patterns
Most weather patterns are quite transient and don't stick around for very long. But sometimes a weather pattern can form which serves as a block and can stick around for a few days or more. There are three main types of blocking patterns.
The first is called a blocking high and is most common in the summer. It happens when a large area of high pressure dominates an area. This high pressure can cause air to sink and can lead to prolonged heat waves.
An omega block can occur when two low pressure systems become detached from the jetstream and an area of high pressure is sandwiched between the two. It is called an omega block because of the way the air flows around these systems in the shape of a capital omega.
A Rex block occurs when an area of high pressure forms poleward of an area of low pressure. This can cause cooler and wetter weather around the low pressure and warmer and drier weather around the high pressure.
