The Omega Block: how this blocking pattern has influenced our recent weather

Weather Blog

Our light at the end of the tunnel has brought us a decent stretch of sunny, dry weather over the past several days. A huge reason for this is due to a specific atmospheric blocking pattern called the Omega Block. First, let’s talk about what exactly a “block” is.

Blocking patterns occur when areas of high and low pressure are lined up in such a way that they prevent each other and other surrounding weather systems from moving. They are essentially “blocking” each other and the weather around it. This results in the weather patterns associated with each other to stall and persist in one area for a prolonged period of time, which can result in very different weather patterns to occur from region to region. 

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. 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.

Depending on which end of the stick you get, it could give you really beautiful weather, or dismal and potentially dangerous weather. The image below shows lower level atmospheric water vapor over the Continental U.S. from yesterday, courtesy of (GOES-East) imagery from the College of DuPage

You can pinpoint the everlasting low pressure system swirling just to our south, the blue and white colors indicating moisture at lower levels, bringing heavy rain to areas over the Carolina’s. Here in WNY, our air at lower levels has been dominated by dry air shown by the yellow and orange colors.

Omega blocks are known to persist for several days at a time which often lead to prolonged periods of warm and dry conditions under the high pressure, and cold, rainy conditions under the low pressure. So, while us here in Rochester and WNY have been receiving dry skies and bright sunshine all week long, the folks over the Carolinas and southern Appalachians have been receiving flooding conditions due to the prolonged periods of rainfall. 

The plus side of getting these weather blocking patterns are that it’s much easier for forecasters to pinpoint exactly what type of weather each region will receive, and we can expect it to last over the next several days.

This pattern doesn’t always guarantee the same weather pattern over the same area. The next time we see an omega block, we may not be so lucky in getting the drier side of things. Heading into this weekend, the blocking pattern will begin to break up and end our 100% dry stretch of weather streak.

~Meteorologist Christine Gregory

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