Guest Post by Alma #Weathercat

Northern Blocking in the UK

Northern blocking is one of the most influential drivers of UK weather. High pressure building interrupts the jet stream’s usual westward flow in the high latitudes of Greenland, Iceland, or Scandinavia. This “block” forces weather systems to divert around it, often locking the UK into a particular pattern for days or even weeks.

Although blocking can occur at any time of year, its effects in winter and spring are dramatically different.

For snow lovers like mummy, northern blocking is a key hope for winter months in the UK and to be in the correct position to bring in winds and snow. 

Northerly flows bring snow showers to Scotland, Northern Ireland, and the eastern coasts.

Easterly flows can produce widespread snow, especially when North Sea convection is strong. People know this weather phenomenon as the Beast from the East.

How winter blocking forms

In winter, the jet stream is stronger and more active. When a northern block forms, it forces the jet to buckle southwards, often sending it through Spain or the Mediterranean. This opens the door for Arctic or continental air to spill into the UK.

The most common winter blocking positions are:

*Greenland High (Greenland block) drives cold north‑westerlies or northerlies into the UK.
*The Scandinavian High (Scandi block) pulls in cold easterlies from Siberia and western Russia.
*Energy demand spikes. Prolonged cold spells increase heating demand and can strain infrastructure.

Why winter blocking is so impactful

Cold air masses are dense and persistent. Once they settle over the UK, they can be very difficult to shift without a major change in the jet stream. That’s why winter blocking often leads to memorable cold spells—think 2010 or the “Beast from the East” in 2018.

Northern Blocking in Spring:

Spring is a transitional season, and blocking behaves differently because the atmosphere is warming, the jet stream weakens, and the contrast between polar and tropical air reduces.

How spring blocking forms

Spring blocks often develop over:

*Greenland
*Iceland
*Scandinavia
*The North Atlantic

But the key difference is that the air masses involved are no longer cold. Instead, the block’s position determines whether the UK gets warmth, chill, or dry settled weather.

It can bring cold, grey days, though, and chilly spring nights. Can also mean a lot of dry weather, which is not welcome in spring for nature, wildlife, and farmers.

The same blocking pattern that brings snow in February might bring sunshine and warmth in May. The key is the temperature of the source air and the strength of the sun. By late spring, even an easterly flow can feel pleasant rather than bitter.