What We Need for a Classic Winter

One of the quirks of UK winter is the “blocking high”. that stubborn ridge of high pressure which parks itself over Greenland or Scandinavia and funnels icy Arctic air towards us. When one of these blocks settles in, we get the sort of winter weather people still get misty-eyed about: crisp days, deep frosts, frozen ponds, maybe even some snow that sticks around long enough to matter.

Why Blocking Highs May Be Harder to Form

There’s a growing theory that these winter blocks are becoming harder to form, and climate change may be the reason why. A warmer planet may be strengthening the jet stream, and that’s bad news for anyone holding out hope for a picture-postcard winter.

As global temperatures rise, the atmosphere gains energy. In the North Atlantic especially, warmer sea surface temperatures can sharpen the contrast between mid-latitude air and the colder air over the Arctic. That contrast acts like fuel for the jet stream. The bigger it is, the more powerful the jet becomes. Instead of drifting in lazy loops, it straightens out into a fast, west-to-east conveyor belt of mild Atlantic air.

Blocking Highs Don’t Stand a Chance

Blocking highs need a slow, wavy jet to form. If the jet is ripping along like a motorway tailwind, any developing block simply gets shunted away before it can anchor itself.

This winter is proving to be a perfect example. Back in early November, many long-range computer models suggested that a blocking high was set to develop next week. This would be the kind of setup winter enthusiasts cling to like a lottery ticket.

The ingredients were there on paper. But every time the atmosphere hinted at forming a block, the real-world jet stream muscled in and flattened it. The models often don’t fully account for how consistently strong the jet has become, so they keep dangling the promise of cold spells that never materialise. The same thing can happen in wet summers, with the Azores High getting crushed along with our spirits.

Cold Winters Aren’t Gone — Just Harder to Achieve

We’ll still see the occasional year where the jet weakens or buckles enough for high pressure to settle in the right place. But if the broader trend is toward a more energetic jet stream in a warming climate, the window for those classic cold setups becomes narrower and easier to spoil.

Climate change may not have cancelled winter, but it is making it harder to pin down. The jet stream is increasingly acting like a winter party-crasher — barrelling in, sweeping away blocking highs, and replacing our hopes of snow with yet another dose of mild, windy rain.

Christmas cards featuring robins sat on a snow covered are becoming little more than a charming myth.