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This text was initially printed at The Dialog. The publication contributed the article to House.com’s Skilled Voices: Op-Ed & Insights.
The summer time of 2025 introduced unprecedented flash flooding throughout the U.S., with the central and jap areas hit notably exhausting. These storms claimed a whole lot of lives throughout Texas, Kentucky and a number of other different states and precipitated widespread destruction.
Each eventualities have been uncommon – and so they have been largely directed by the polar jet stream.
What’s a jet stream?
Jet streams are slim 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 major jet streams:
The polar jet stream is usually 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 chilly storms down from Canada.
The subtropical jet stream is usually nearer to 30 levels latitude, which within the Northern Hemisphere crosses Florida. It follows the boundary between tropical air plenty and subtropical air plenty. 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 (sooner) 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 time 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 usually attributable to localized convection because of uneven heating of the land – image afternoon pop-up thunderstorms.
Throughout 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 essential penalties.
First, as a substitute of shifting storms rapidly 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 plentiful 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 larger 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 turned 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 warmth waves.
The jet stream buffered US in hurricane season
The jet stream additionally performed a task within the 2025 hurricane season.
Given its west-to-east wind course, the southward dip of the jet stream – together with a weak excessive stress system over the Atlantic – helped steer all 5 hurricanes away from the U.S. mainland.
Many of the 12 months’s 13 tropical storms and hurricanes veered off into the Atlantic earlier than even reaching the Caribbean.
Local weather change performs a task in these shifts
So, how does local weather change affect the jet stream?
The energy of jet streams is managed by the temperature distinction 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 greater than twice the worldwide common fee, and that’s lowering the equator-to-pole temperature distinction. As that temperature gradient weakens, jet streams lose their energy and turn into extra susceptible to stalling.
This will increase the chance of persistent excessive rainfall occasions.
Weaker jet streams additionally meander extra, producing bigger waves and extra erratic conduct. This will increase the chance of surprising shifts, such because the southward swing of the jet stream in the summertime of 2025.
A latest research discovered that amplified planetary waves within the jet streams, which might trigger climate programs to remain in place for days or perhaps weeks, are occurring thrice extra continuously than within the Fifties.
What’s forward?
As the worldwide local weather continues to heat, excessive climate occasions pushed by erratic conduct of jet streams are anticipated to turn into extra widespread. Mixed with extra moisture that hotter oceans and air plenty provide, these occasions will intensify, producing storms which are extra frequent and extra damaging to societies and ecosystems.
Within the quick time period, the polar jet stream will likely 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 chilly air outbreaks.
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