Summer 2025 will be remembered as a season of extremes across the United States: deadly flash floods inundated communities from the Plains to the Mid-Atlantic. Yet not a single hurricane made landfall.
This apparent paradox puzzled many observers. To atmospheric scientists, the key lies in the unusual behavior of one of the atmosphere’s most powerful features: the polar jet stream.
How the Polar Jet Stream Shapes Our Weather
The polar jet stream is a fast-moving ribbon of air blowing from west to east high in the atmosphere, roughly 30,000 to 40,000 feet above the ground. These winds, often exceeding 100 mph, act as a kind of atmospheric “conveyor belt,” steering storm systems and helping determine where rain, snow, and severe weather will occur.
In a typical summer, the polar jet retreats northward into Canada and weakens. This allows much of the continental U.S. to experience relatively calmer, more stable weather patterns.
In 2025, however, the jet stream did something very different. The consequences were profound.
An Unusual Southward Shift and Weakening
Instead of pulling back to the north as it usually does in summer, the polar jet stream in 2025 shifted unusually far south and weakened. This combination fundamentally reshaped weather patterns across North America.
Because the jet was weaker, it became sluggish, allowing weather systems to move more slowly than normal. Rather than sweeping storms quickly across the country, the atmosphere effectively “stalled” them over the same regions for days at a time.
From Stalled Storms to Catastrophic Flooding
The most direct consequence of this stalled jet pattern was a series of devastating flash floods. When storms linger instead of moving along, rainfall accumulates rapidly over localized areas, overwhelming rivers, drainage systems, and soils that simply cannot absorb water fast enough.
Prolonged Downpours Over the Same Areas
This sluggish jet stream pattern repeatedly parked storm systems over the same states, producing:
These conditions combined to produce catastrophic flooding that claimed hundreds of lives. Extensive infrastructure damage occurred across large swaths of the U.S.
Gulf Moisture Supercharging Rainfall
The jet stream’s exaggerated north–south meanders—large atmospheric “waves”—also played a critical role. The southward dips helped funnel warm, humid air from the Gulf of Mexico far inland.
This moisture-rich air mass acted as fuel for intense rainfall. When that warm, moisture-laden air was lifted along frontal boundaries or storm systems, it condensed into heavy rain and powerful thunderstorms.
The result was supercharged rainfall: storms with higher rain rates than would otherwise occur. This greatly increased flood risk.
The Role of Exceptionally Warm Oceans
Another key factor in the Summer 2025 extremes was the state of the surrounding oceans. Sea surface temperatures in both the Atlantic and the Gulf of Mexico were exceptionally warm, providing extra energy and moisture to the atmosphere.
Warm Waters, More Moisture, Stronger Convection
Warm ocean waters enhance evaporation, loading the lower atmosphere with water vapor. This has two critical effects:
In 2025, this oceanic “boost” intensified the rainfall associated with already slow-moving systems. Many events were pushed from serious to truly catastrophic.
Persistent High-Pressure Systems and Heat Waves
Overlaying all of this was the influence of persistent high-pressure systems. These areas of sinking air effectively “locked” the wavy jet stream in place, preventing it from shifting into a new pattern.
Locked Patterns: Floods in Some Regions, Heat in Others
Where low-pressure systems repeatedly formed and stalled, communities faced round after round of flooding. Meanwhile, under the domes of high pressure, other regions endured intense heat waves.
Clear skies and sinking air led to prolonged, oppressive heat. This kind of blocked pattern—with the jet stream stuck in a highly distorted shape—can produce simultaneous, contrasting extremes: floods in one region, drought or heat in another.
Why No Hurricanes Made U.S. Landfall
At first glance, it seems surprising that a summer with such severe flooding saw no hurricanes strike the U.S. mainland. Yet here again, the jet stream was a central player.
Steering Currents Pushed Hurricanes Away
The same southward dip in the polar jet, combined with unusually weak high pressure over the Atlantic, acted like a steering mechanism that guided all five hurricanes away from the U.S. coast. Instead of being drawn toward the Gulf Coast or Eastern Seaboard, these storms curved out to sea or were diverted toward other regions.
This highlights an important point: extreme impacts do not require hurricane landfalls. In 2025, the combination of jet stream configuration and moisture-laden storms was more than enough to generate a season of devastating hydrologic extremes.
Climate Change and the Future of Stalled Extremes
Underlying these events is a broader, long-term trend associated with human-driven climate change. As the Arctic warms faster than the tropics, the temperature contrast between the equator and the poles is weakening—a key ingredient in the strength of the jet stream.
Weaker, Wavier Jets and Rising Risk
A reduced equator-to-pole temperature gradient tends to produce jet streams that are weaker and more prone to large meanders.
When those meanders become locked in place, the result is an increased likelihood of:
The Summer 2025 flash floods—occurring even in the absence of hurricane landfalls—offer a stark illustration of how a changing climate and a more capricious jet stream can combine to produce deadly, costly weather disasters.
Here is the source article for this story: 2025’s extreme weather brought intense flash flooding, but no hurricane landfalls in the US – the jet stream is a big reason why