Storms That Linger in a Warming World
A new study warns that a warming climate will bring high-intensity, prolonged rainfall, floods, and ozone transport to the Northern Hemisphere.
Breaking the Ice:
A new study offers a stark new forecast: intense, long-lasting Cut-Off Lows (COLs) are likely to become more frequent across the Northern Hemisphere, especially during spring. COLs are mid- to upper-tropospheric storms that detach from the jet stream and meander slowly across regions—often unleashing prolonged and heavy rainfall.
Until now, there has been no comprehensive climate model-based projection for COLs. The authors analyzed 18 global climate models under the high-emissions SSP5-8.5 scenario—essentially a worst-case future. Their findings? Up to 80% of these models show that long-lasting and intense COLs will increase significantly over land regions, particularly in Europe, North America, and East Asia during spring. This shift represents not only a change in storm frequency, but potentially a major uptick in climate-related hazards.
Quick Melt:
The slow, erratic paths of COLs make them particularly hazardous. Their ability to linger means more time for rainfall to accumulate, overwhelming natural and built drainage systems. The study finds that while some projected increases in propagation speed might marginally mitigate their hazards, the overall trend remains clear: more frequent, more intense, and longer-lasting COLs are likely.
For Europe in particular, the study predicts the traditional summer “COL season” will begin earlier—shifting into spring and bringing with it heavier, potentially catastrophic rainfall. North America and East Asia are expected to see similar seasonal shifts. Alarmingly, it's the COLs that linger beyond three days—often the most destructive—that are projected to increase the most. These long-lived systems also have stronger vorticity, meaning they're not just persistent—they’re powerful.
COLs are also known to transport ozone from the stratosphere into the troposphere. This has profound implications beyond rain and flooding: tropospheric ozone is a greenhouse gas, a pollutant, and a threat to human and ecological health. An uptick in these systems could enhance surface ozone concentrations and disrupt agriculture and public health outcomes in regions already strained by heat and pollution.
Yet there’s a faint silver lining. The study notes that faster-moving COLs in some seasons may reduce the duration of rainfall, and by extension, the severity of flooding. But this offset isn’t guaranteed, and model uncertainties—particularly over jet stream dynamics and atmospheric blocking—underscore the complexity of predicting these systems with precision. Still, the trend is unmistakable: intense COLs are becoming a bigger part of our climate future.
The Thaw:
Don’t Understand the Atmospheric Mechanics of Cut-Off Lows? AccumulationZone Explains.
COLs are upper-level low-pressure systems that become detached from the main jet stream. This separation occurs when the jet—normally a coherent west-to-east flow of high-altitude winds—undulates to such a degree that a pocket of cold air gets isolated and stalls over a region. This process, known as Rossby wave breaking, effectively “cuts off” the low from the dominant atmospheric circulation.
The result is a slow-moving system with the potential for days of sustained precipitation. Unlike fast-moving frontal storms, COLs tend to remain nearly stationary, creating localized, high-impact weather—flooding, landslides, and in some cases, stratospheric ozone intrusions that can degrade air quality and affect radiative forcing.
What makes COLs particularly sensitive to climate change is their dependence on jet stream dynamics. As the Arctic warms more rapidly than mid-latitudes, the temperature gradient that powers the jet stream weakens. This leads to a more meandering and sometimes sluggish jet, increasing the likelihood of wave breaking and the formation of COLs. Moreover, projections indicate a poleward shift and seasonal change in jet behavior, which may explain the increasing frequency of springtime COLs over Europe and North America.
The study’s finding that long-lasting and intense COLs will become more common suggests not only a change in storm patterns, but also a shift in how and when extreme rainfall events occur. And while some increases in propagation speed may help reduce storm duration, this dynamic appears insufficient to offset the broader rise in hazard potential.
Final Thoughts
For communities across the Northern Hemisphere, this research is both a warning and a call to prepare. More frequent, long-lasting COLs mean more infrastructure stress, more crop damage, and heightened flood risks. Understanding the dynamics behind these storms—how they form, why they intensify, and where they're likely to strike—can help shape better forecasting, urban planning, and climate adaptation strategies.