Two dominant forces will influence our conditions through the coming days and potentially beyond.
The interplay between these opposing drivers means the forecast is far from straightforward, and many areas are likely to experience a mixture of weather types rather than a single prevailing pattern.
Cold air gathering to the northeast
One of the key players in the forecast is a pool of cold air developing across Scandinavia and extending into the North Sea by the weekend. Although the very coldest air will remain further northeast, the UK will get a taste of it—most notably across northern and eastern areas by early next week. If this were the only factor at play, the outlook would be much simpler: cold easterly winds, snow showers and temperatures well below average. But the broader global picture is exerting an equally influential pull.
A surge of very cold air across North America
While cold air gathers to our northeast, another major outbreak of Arctic air is plunging south across Canada and into parts of the United States. Some areas, including New York state, are expected to see maximum temperatures as low as –7°C by the end of the week. This cold air will not reach the UK directly, but its presence has an important knock‑on effect. When such outbreaks occur, they collide with milder air further south, sharpening the temperature contrast and fuelling a more powerful jet stream. We saw a similar pattern earlier in December, and it is happening again now.
A more powerful but south‑shifted jet stream
As the jet stream strengthens across the North Atlantic, it takes a slightly more southerly track than usual. This shift allows deeper Atlantic low‑pressure systems to move towards the UK, bringing spells of wet and windy weather through the weekend and into next week. These systems then meet the colder, drier air to the northeast. The result is a highly changeable mix—neither straightforwardly mild, wet and windy, nor consistently cold with easterly winds. Different parts of the UK will experience different dominant influences, and these may fluctuate day by day.
READ MORE: What is the jet stream?
Slow‑moving systems and significant rainfall
The clash between a strengthened jet stream and encroaching cold air means weather systems will slow down, increasing the potential for prolonged rainfall. Eastern Scotland is a particular concern, with southeasterly winds forcing moisture‑laden air over the hills. Rainfall totals of 60mm are expected widely, with over 100mm possible on higher ground. Warnings are already in force, and there is a risk of flooding. Elsewhere across the UK, many areas will see 50mm or more of rain up to the end of the week especially in western and southern regions.
An area of low pressure, will bring spells of heavy rain and strong winds across much of southwest England on Friday before easing on Saturday morning. The system is slow-moving but will bring more than 20mm of rain for some which is falling on saturated ground, increasing the chances of impacts. In addition to rain, large waves and gusty winds are likely, especially along southern coasts, with 60mph peaks possible, with 45-50mph inland.
The weekend: colder easterly winds developing
By the weekend, low pressure remains close by but begins to weaken and drift slowly away. This allows an easterly flow to develop, drawing in colder air. Saturday will still bring showers, strong winds and further rain or hill snow in the northeast. Temperatures in eastern areas will struggle at around 5–6°C. Sunday turns even colder, with a mix of showers in the northwest and far south, but many central areas seeing brighter, drier spells. Showers in the northeast may fall increasingly as sleet or snow, especially on hills.
READ MORE: Understanding the Met Office’s WeatherReady preparedness work
Monday and Tuesday: the first clash of air masses
As colder air becomes established, the next Atlantic system approaches on Monday, bringing a band of heavy rain into Northern Ireland, Wales and southwest England. However, as this encounters the colder air, it may turn to snow in places. The exact location depends on the orientation of the low pressure and subtle changes in its track. Some model simulations place the low slightly further south, increasing the chance of snow on its leading edge before turning back to rain. Others suggest a more northerly track with fewer wintry hazards.
Why the forecast remains uncertain
Computer models are run multiple times to account for small variations in starting conditions, which can lead to significantly different outcomes—a reflection of the atmosphere’s chaotic nature. A slightly weaker or stronger cold pool across North America, for instance, could alter jet‑stream strength and shift the balance between easterlies and Atlantic lows over the UK. Some simulations keep the UK in a colder, easterly flow; others bring milder, wetter conditions from the southwest. Both scenarios remain plausible.
Further low‑pressure systems are expected mid‑week, and their latitude and depth will determine whether milder or colder air takes hold. In reality, a blend of both scenarios is likely: wetter, windier weather at times in the southwest; colder and drier conditions in the northeast; and the continued risk of some snow where the two air masses meet.
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