Breakdown: What is an ‘Omega Block’ and why it can last a while

MEMPHIS, Tenn. (WMC) - The bulk of our weather is driven by the movement of high and low pressure systems across the U.S. from west to east.

The omega block pattern that has been over the U.S. this past week has featured lower pressure over the western U.S., high pressure over the central plains, and lower pressure once again over the eastern U.S. just to our south.

An Omega Block is a weather pattern in the upper levels that, when plotted on a map, resembles the Greek letter Ω (Omega).

Omega blocks are named due to pattern they form which resembles the uppercase Greek letter... — Omega blocks are named due to pattern they form which resembles the uppercase Greek letter omega, Ω.(WMC)

An Omega Block forms when an area of high pressure becomes sandwiched between two areas of low pressure. Warm and dry air is found under the high, while cool and stormy weather is found on either side of the block.

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.

Omega blocks are known to persist for several days at a time, which is where the “block” terms dervives from as these patterns can be stubborn to move.

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