This text was initially printed at The Conversation. The publication contributed the article to Area.com’s Knowledgeable Voices: Op-Ed & Insights.
The summer time of 2025 introduced unprecedented flash flooding throughout the U.S., with the central and japanese areas hit significantly onerous. These storms claimed hundreds of lives across Texas, Kentucky and several other different states and triggered widespread destruction.
Each eventualities have been uncommon – and so they have been largely directed by the polar jet stream.
What is a jet stream?
Jet streams are narrow bands of high-speed winds within the higher troposphere, round 4 to eight miles (seven to 13 kilometers) above the floor of the Earth, flowing west to east across the whole planet. They kind the place sturdy temperature contrasts exist.
Every hemisphere hosts two main jet streams:
The polar jet stream is often discovered close to 50 to 60 levels latitude, throughout Canada within the Northern Hemisphere, the place chilly polar air meets hotter midlatitude air. It performs a serious position in modulating climate programs within the midlatitudes, together with the continental U.S. With winds as much as 200 mph, it is also the standard steering pressure that brings these bitter cold storms down from Canada.
The subtropical jet stream is often nearer to 30 levels latitude, which within the Northern Hemisphere crosses Florida. It follows the boundary between tropical air lots and subtropical air lots. It’s typically the weaker and steadier of the 2 jet streams.
These jet streams act like atmospheric conveyor belts, steering storm programs throughout continents.
Stronger (quicker) jet streams can intensify storm programs, whereas weaker (slower) jet streams can stall storm programs, resulting in extended rainfall and flooding.
2025’s intense summer of flooding
Most summers, the polar jet stream retreats northward into Canada and weakens significantly, leaving the continental U.S. with calmer climate. When rainstorms pop up, they’re sometimes attributable to localized convection due to uneven heating of the land – image afternoon pop-up thunderstorms.
Through the summer time of 2025, nevertheless, the polar jet stream shifted unusually far south and steered bigger storm programs into the midlatitudes of the U.S. On the identical time, the jet stream weakened, with two crucial penalties.
First, as a substitute of shifting storms shortly eastward, the sluggish jet stream stalled storm programs in place, inflicting extended downpours and flash flooding.
Second, a weak jet stream tends to meander extra dramatically. Its broad north-south swings in summer time 2025 funneled humid air from the Gulf of Mexico deep into the inside, supplying storm programs with considerable moisture and intensifying rainfall.
This moisture surge was amplified by unusually heat situations over the Atlantic and Gulf areas. A hotter ocean evaporates extra water, and hotter air holds a better quantity of moisture. Because of this, extraordinary ranges of atmospheric moisture have been directed into storm programs, fueling stronger convection and heavier precipitation.
Lastly, the wavy jet stream grew to become locked in place by persistent high-pressure programs, anchoring storm tracks over the identical areas. This led to repeated episodes of heavy rainfall and catastrophic flooding throughout a lot of the continental U.S. The identical conduct can go away different areas dealing with days of unrelenting heat waves.
The jet stream buffered US in hurricane season
The jet stream also played a role in the 2025 hurricane season.
Given its west-to-east wind direction, the southward dip of the jet stream – along with a weak high pressure system over the Atlantic – helped steer all five hurricanes away from the U.S. mainland.
Most of the year’s 13 tropical storms and hurricanes veered off into the Atlantic earlier than even reaching the Caribbean.
Climate change plays a role in these shifts
So, how does climate change influence the jet stream?
The strength of jet streams is controlled by the temperature contrast between the equatorial and polar areas.
A better temperature distinction results in stronger jet streams. Because the planet warms, the Arctic is heating up at more than twice the worldwide common fee, and that’s decreasing the equator-to-pole temperature distinction. As that temperature gradient weakens, jet streams lose their power and turn into extra vulnerable to stalling.
This will increase the danger of persistent excessive rainfall occasions.
Weaker jet streams also meander more, producing bigger waves and extra erratic conduct. This will increase the chance of bizarre shifts, such because the southward swing of the jet stream in the summertime of 2025.
A current examine discovered that amplified planetary waves in the jet streams, which might trigger climate programs to remain in place for days or perhaps weeks, are occurring thrice extra ceaselessly than within the Nineteen Fifties.
What’s ahead?
As the global climate continues to warm, extreme weather events driven by erratic behavior of jet streams are expected to become more common. Mixed with further moisture that hotter oceans and air lots provide, these occasions will intensify, producing storms which are extra frequent and extra harmful to societies and ecosystems.
Within the quick time period, the polar jet stream can be shaping the winter forward. It’s strongest in winter, when it dips southward into the central and even southern U.S., driving frequent storm programs, blizzards and cold air outbreaks.
