Omega Block

Sources: Various internet sites

The Omega Block is a specific blocking pattern that exists when an area of high pressure is sandwiched between two areas of lower pressure. They typically consist of a low-high-low pattern from west to east. When viewing this pattern in the upper levels of the atmosphere it resembles the Greek letter omega, hence where it gets its name.


The bulk of our weather is driven by the movement of high and low pressure systems across the U.S. from west to east. Air flows counterclockwise around the lows and clockwise around the high, resulting in the huge "ridge" between the lows. This ridge forces the jet stream up and around it which means air doesn't flow from west to east like normal. Instead it flows north and south.

Warm and dry air is found under the high, while cool and stormy weather is found on either side of the block. Depending on your location, it could give you really beautiful weather, or dismal and potentially dangerous weather. Under those mid level lows, the weather is yucky. Under the influence of the high, the weather is great.

Omega blocks are known to persist for several days at a time, which is where the "block" term derives from as these patterns can be stubborn to move.