A weather phenomenon has been impacting central and eastern Iowa Saturday in the form of persistent cloud cover. This pattern is called an “omega block”.

An omega block is a weather setup in the upper atmosphere that looks like the Greek letter omega (Ω) (see image). Shown is a big area of high pressure parked in the atmosphere, with two low-pressure systems spinning on either side.

It’s caused by the jet stream buckling into a sharp ridge of high pressure, flanked by deep troughs. This pattern is like a stubborn roadblock in the sky—it can stall out for days or even weeks.

Where that high pressure sits, you’re looking at clear skies and dry, warm weather. But those lows on the sides? They’re churning up storms, rain, or cooler temps.

So, if an omega block sets up, get could be in for some persistent weather: lots of sunshine or relentless rain, depending on where you are!