An Omega Block Pattern - 47 ABC - Delmarva's Choice

An Omega Block Pattern


Have you ever heard of an Omega Block? Well, it's actually a type of weather pattern. It's called an Omega Block because the height lines in the upper-levels of the atmosphere resemble the shape of the Greek letter Ω (Omega).

Attached is an image of today's upper-level chart at 500 millibars, which shows the current conditions miles high in the sky. The 500 millibar weather chart shows both height lines and also sea level pressure lines. The height lines are also known as the steering winds of the atmosphere, steering our weather systems. It's these height lines we look at to see where storms may move and also to help us determine if we are in an Omega Block.

Based on today's chart, it appears an Omega Block is currently set up across the eastern half of the country. It's not a classic block, but it is close. An Omega Block is a type of blocking pattern where an area of high pressure is between two areas of low pressure.

The high pressure in the middle pushes the jet stream north into Canada. This moves Pacific air north over the high pressure system and then south again into the U.S around the high. This ultimately blocks or protects areas within the high pressure from bad weather. Areas under the high pressure typically experience dry weather while areas under the low pressure experience wetter weather. These blocks can last for days, if not weeks, and can dump lots of rain on places underneath the low pressures.

This explains the sunny and dry weather we experienced this past weekend. Unfortunately this block is breaking down. The high pressure is heading east away from us and the low near Oklahoma is heading towards us, meaning it's our turn to experience cloudy and rainy weather for a few days.

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