If you were planning for a dry weekend this past weekend and instead found yourself dodging raindrops, you’re not alone, and you’re not crazy. It was supposed to be mostly dry across much of Missouri and southern Illinois. But as every seasoned meteorologist knows, the atmosphere likes to keep us humble. Enter one of the more frustrating patterns in the jet stream: the Omega Block.
The Omega Block gets its name from the shape it forms on the upper-level jet stream, resembling the Greek letter Ω. It’s a classic high-pressure ridge “blocked” by low-pressure systems on both sides. When this pattern sets up, everything in the atmosphere stalls. Storm systems slow down or get trapped, and weather that should move out… doesn’t. In our case, models originally placed the high-pressure ridge right over our region, which would have delivered sunny, warm, and dry weather. But the ridge nudged just a bit east, allowing an upper-level low to settle in over the Mississippi/ Ohio River confluence. This meant the dry air got pushed away, and the circulation around the low began pulling in moisture, leading to more cloud cover and on-and-off showers, especially across southeast Missouri and southern Illinois.
This pattern is notoriously difficult to break. While the central high-pressure ridge remains dominant, the low on either side keeps spinning, reinforcing the block. That’s why many locations along and east of I-55 ended up with several days of drizzle or rain despite earlier dry forecasts.
Omega Blocks aren’t rare, but they have a high impact on our weather forecast, not because they cause extreme weather directly, but because they freeze the forecast in place. Whether it’s sunny and dry or wet and unsettled, the pattern doesn’t budge for days. And that’s exactly what happened to us.
So, next time your sunny forecast turns cloudy without much warning, remember it might not be your meteorologist’s fault; rather, it might just be the Omega Block holding us hostage in the atmosphere.
Until next time, take care of yourself!
