Winter is coming

Winter is coming

Tue, 24/11/2020 - 12:07
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The maps above show the UK winter (Dec, Jan, Feb) averages for 1981-2010. The analyses are based on 1 km grid-point data sets which are derived from station data (Source: Met Office)

As we approach the winter season and temperatures start to dip, we take a look at winter weather in the UK – what affects it, seasonal extremes, what an ‘average’ winter looks like and link to some ‘wintry’ articles of interest.

Winter in the UK runs from December to February (although November often suffers very wintry conditions, too). The season is generally cool, wet, windy and cloudy. Temperatures often get as low as freezing point, but rarely much lower than -10°C. This can lead to frost in the mornings and ice on car windscreens, pavements and roads. During the daytime, temperatures rarely rise above 15°C, with coastal areas experiencing milder temperatures due to proximity to the warmer sea.

Precipitation is plentiful throughout winter, however snow is relatively infrequent in most areas, except at higher altitudes such as the Scottish Highlands and the Pennines, where snow can lie for 1-6 months. When it does fall at lower altitudes, it usually affects northern and eastern areas, and higher ground in Wales. Of course, the UK can suffer extreme winters, such as the winter of 1963 and even as recent as December 2010.

The winter months are also unsettled and stormy, especially during the early part of the season. The predominance of storms during this time of the year has led to the Met Office and Met Éireann to define a storm naming system each season.

During periods of light winds and high pressure in winter, frost and fog can become a problem and can pose a major hazard for drivers on the roads.

Since our winters are usually very wet and windy, it is wise to have umbrellas and warm, waterproof clothing to hand!


Winter air mass types

Tropical maritime (Tm)

The source region for this air mass is warm waters of the Atlantic Ocean, between the Azores and Bermuda, with the predominant wind direction being south-westerly. This is a mild air stream and during the winter month it can raise the air temperature several degrees above the average.

Polar continental (Pc)

This air mass originates over the snow fields of Eastern Europe and Russia. It is only considered a winter phenomena. The weather characteristics of this air mass depend on the length of time spent over the sea during its passage from Europe to the British Isles: if the sea track is short, the air is inherently very cold and dry, with weather characterised by clear skies and severe frosts. If the track is longer over the North Sea, the air becomes unstable and moisture is added giving rise to showers of rain or snow, especially near the east coast of Britain. The lowest temperatures across the British Isles usually occur in this air mass, lower than -10 °C at night, and sometimes remaining below freezing all day.

Polar maritime (Pm)

This air mass has its origins over northern Canada and Greenland and reaches the British Isles on a north-westerly air stream. It is the most common air mass to affect the British Isles. This air mass starts very cold and dry but during its long passage over the relatively warm waters of the North Atlantic its temperature rises rapidly and it becomes unstable to a great depth. Pm is characterised by frequent shower, and in the winter months when instability (convection) is most vigorous over the sea, hail and thunder are common across much of the western and northern side of the British Isles.

Arctic maritime (Am)

An arctic maritime air mass originates over the North Pole and the Arctic Ocean. An arctic maritime air mass has similar characteristics to a polar maritime air mass, but because of the shorter sea track the air is colder and less moist. During winter months, the air is cold enough to produce hail showers or snow, and these are most frequent over Scotland and along the coasts exposed to northerly winds. Polar low-pressure systems forming in this air mass can sometimes lead to widespread and heavy snowfall, but otherwise inland areas remain free of cloud in the winter months. In northern Scotland, arctic maritime is usually the coldest air mass, but over the rest of Britain, this air mass is not as cold as polar continental.

Returning polar maritime (rPm)

Returning polar maritime is another version of polar maritime, but this time with a longer seas track which first takes the air southwards over the North-Atlantic, then north-eastwards across the British Isles. During its passage south, the air becomes unstable and moist but on moving north-east it passes over cooler water making it stable in its lowest layers. Although the weather across the British Isles in this air mass is largely dry, there can be extensive Low-level clouds.

Here is a video from the Met Office explaining Air Masses:


Winter statistics

Winter averages (1981-2010):

  • Average Minimum Temperature: 0.8°C
  • Average Maximum Temperatures: 6.6°C
  • Average Mean Temperature: 3.7°C
  • Average Daylight Hours: 158 hours
  • Average Rainfall (mm): 330 mm

Data from 1929 to present can be viewed here >> 

December 2010 was the coldest December in over 100 years with widespread snow across the UK, with snow lying at more than 83% of official weather stations; the highest amount of snow cover ever recorded in the UK.  Overall, winter 1963 was the coldest winter on average.

December has on average 3.9 snow days of 3.9 snow days, followed by 5.3 days, 5.6 days and 4.2 days in January, February and March respectively. 


tWC articles of interest

Dreaming of a white Christmas?

The Big Freeze of 1963: One of the coldest winters on record

Stormy UK Winter 2013 - 2014 most 'energetic' on record

How does hoar frost form?

What causes these beautiful frost patterns?

A traveller’s guide to Reykjavík

‘I tried to catch the fog... but I mist!’ Fog 101

High risk of 'unprecedented' winter rainfall

Biometeorology: Weather and Health

A-Z weather