Why Do Weather Systems Stay in Place for Longer?

Persistent Weather Patterns: Blocking Events

• Meteorological blocks (blocking highs or anticyclones) are large-scale high-pressure systems that remain nearly stationary, stopping or redirecting the usual movement of weather fronts. These blocks can last from several days to weeks, leading to prolonged periods of similar weather for areas underneath or adjacent to them—such as extended droughts, heatwaves, or persistent rain.wikipedia+3

• The jet stream—a fast-flowing ribbon of air high up in the atmosphere—usually transports weather systems from west to east. When this stream develops exaggerated “waves” (is more wavy or slows down), its swings can become persistent, and weather systems get stuck in one place for a longer time. This wavy jet stream pattern is increasingly observed, especially with ongoing Arctic warming.arctic-council+2

Climate Change and Blocking Events

• Evidence suggests that climate change is affecting blocking events. Research indicates that the size of these stalled systems is increasing—up to 17% bigger in the Northern Hemisphere as the century progresses—meaning that persistent weather affects larger areas and potentially exposes more people to extremes. That translates to more severe and widespread impacts, such as deadly heat waves and floods.nsf+1

• While it's unclear if the overall frequency or duration of blocking events is increasing, their extent (how much land they cover) is projected to grow, and the unpredictability of their occurrence may increase due to climate change. Models sometimes underestimate how often these blocks happen, making them a challenge for forecasting and research.carbonbrief+1

Types of Blocking Patterns

• Omega blocks: Area of high pressure trapped between two lows, resembling the Greek letter Ω. Tends to be stubborn and slow-moving.

• Diffluent blocks: Occur when the usual west-to-east flow splits, allowing a stationary high-pressure area to persist.metoffice

Regional Effects and Notable Events

• Notable heat waves and floods in recent decades—such as those in France (2003), Russia (2010), Western North America (2021), and Australia—were driven by blocked weather systems that stalled for days to weeks. These blocks led to record-breaking temperatures, flooding, and drought.theconversation+1

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Key Takeaways

• Weather systems are staying in place longer mainly due to persistent blocking events, often amplified by changes to the jet stream and climate change.

• These persistent blocks can bring extreme, prolonged weather—be it heat, rain, or cold—to affected regions.

• The size of these stalled systems is likely increasing with climate warming, impacting larger regions and populations.nsf+1

1. https://en.wikipedia.org/wiki/Block_(meteorology)
2. https://arctic-council.org/news/shifting-winds-how-a-wavier-polar-jet-stream-causes-extreme-weather-events/
3. https://www.carbonbrief.org/jet-stream-is-climate-change-causing-more-blocking-weather-events/
4. https://www.nsf.gov/news/stalled-weather-patterns-will-get-bigger-due
5. https://theconversation.com/stalled-weather-how-stuck-air-pressure-systems-drive-floods-and-heatwaves-178157
6. https://www.metoffice.gov.uk/weather/learn-about/weather/how-weather-works/high-and-low-pressure/blocks
7. https://icewatch.co.uk/news/understanding-weather-systems/
8. https://www.reddit.com/r/meteorology/comments/uvc9hz/are_high_pressure_systems_always_associated_with/