New York is cool, Texas is frying. Blame this strange jet stream jam

• An Omega Block weather pattern is causing varied weather across the United States this week.
• This pattern creates a high-pressure zone in the center of the country, bringing heat, and low-pressure zones on the coasts, causing storms.
• Severe thunderstorms are expected in the Central Plains and Mississippi Valley, with rain along the East Coast.
• The Omega Block is forecast to persist through the weekend before conditions normalize next week.

This story has been updated to include additional information.

If you’re in New York, you might be reaching for a jacket. In Texas, the air conditioner is running nonstop. Meanwhile, one part of the U.S. is stuck in early spring chill, and another faces brutal storms.

The reason isn’t random — it’s a stalled pattern high above the country that’s locking weather into place.

A large-scale atmospheric pattern known as an Omega Block is helping organize a busy and highly divided weather setup across the United States this week, supporting severe thunderstorms in the Plains, mountain snow in the West and steady rain along parts of the East Coast.

The pattern, named for its resemblance to the Greek letter Ω in the jet stream, is slowing the typical west-to-east movement of weather systems. That slowdown is allowing multiple fronts and storm systems to linger and repeatedly impact the same regions.

Here's what it means for weather across the U.S.

What is an Omega Block?

An Omega Block is a large-scale weather pattern in the jet stream that slows the atmosphere down and locks weather in place for several days, according to the National Oceanic and Atmospheric Administration.

It forms when the jet stream bends into a big loop shaped like the Greek letter “Ω.” In the middle of that loop is a strong area of high pressure. On both sides are areas of low pressure.

That setup splits the country into three zones. In the center, under the high pressure, skies are usually clear and sinking air allows heat to build and stay put — often bringing a long stretch of hot weather across the Plains and into the South, with widespread 80s and 90s.

On the edges of the pattern, the low-pressure systems take over. Those areas are cooler and cloudier, with rain and thunderstorms that can linger because the pattern is slow to move.

The result is a stuck weather pattern: heat trapped in the middle, and stormier, cooler conditions on either side.

Where storms are expected

The highest severe weather risk is centered on parts of the Central Plains Thursday, expanding into the Middle Mississippi Valley Friday into early Saturday, according to the Weather Prediction Center.

Storms that develop along the front could organize into clusters or lines, increasing the risk for damaging winds and large hail. Forecasters also note a small tornado threat, especially where instability and wind shear overlap. Rainfall could become more widespread and locally heavy as storms repeat along the boundary.

In the Northeast and Southeast, rain and thunderstorms will continue along the Eastern Seaboard through Friday morning before the system moves offshore, according to the Weather Prediction Center.

Farther south, a lingering front over Florida will keep showers and thunderstorms in place through Saturday, though widespread severe weather is not expected at this time.

How long does an Omega Block last?

Omega Blocks typically persist for several days to about one to two weeks, depending on how strongly the jet stream pattern is locked in.

The key factor is whether surrounding weather systems are strong enough to dislodge the ridge in the middle. If they are not, the pattern can remain stagnant, prolonging heat in some areas and repeated storm chances in others.

Once the block breaks down, the transition can be relatively quick — allowing the jet stream to return to a more typical west-to-east flow and shifting storm tracks again.

For this week, forecast models suggest the block will remain in place long enough to support multiple rounds of severe weather through the weekend, but conditions are set to return to normal for much of the U.S. early next week.

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Brandi D. Addison covers weather across the United States as the Weather Connect Reporter for the USA TODAY Network. She can be reached at [email protected]. Find her on Facebook here.