Will January see any cold snaps or snow in Ireland or the UK
In what was a rather mild and settled Christmas period with higher temperatures than normal here in Ireland and the UK that trend continued into 2020 but this weekend the weather will turn much more unsettled and looking ahead that is the general pattern that looks set to last the next 10 days.
The reason for mild and unsettled weather over the months of November and December was due to a strong jet stream which give us a unsettled westerly flow. Even though there was some areas that seen snow this was due to the jet stream briefly dropping southwards allowing colder air to effect us and much of the small amounts of snow was due to weather systems moving in from the Atlantic and mixing with the colder air.
Some parts of Ireland seen above average amounts of rainfall at times with England and Wales also seen large rainfall amounts leading to some severe flooding in places due to the volumes of water and heavily saturated ground.
Even Europe so far this winter has seen more milder weather than colder weather with no major cold snaps but the main reason for this is the strong polar vortex which currently sits over the Arctic
What is the Polar Vortex?
The polar vortex is a circulation of winds high up in the stratosphere, up to 30 miles (50 km) above the earth. It is present in winter, and is not a new phenomenon, scientists have known about it for many years.
The winds regularly exceed 155 miles per hour (250 km per hour) – the strength of the winds in the strongest hurricanes (known as Category 5).
During the winter it can strengthen and weaken. These changes exert an influence lower down in the atmosphere and ultimately on our weather.
How does the Polar Vortex affect our weather?
A strong polar vortex favours a strong jet stream. The jet stream is a fast moving ribbon of air around 5 to 7 miles (8 to 11km) above the earth that drives weather systems from the Atlantic towards the Ireland and the UK.
Conversely, when the polar vortex weakens, the jet stream also tends to weaken and become distorted.
In a typical Ireland and UK winter, the jet stream brings winds from the west giving us our mild, damp climate.
With a stronger jet stream, stormy and very wet weather tends to occur. A weaker jet stream allows more frequent spells of northerly or easterly winds to affect the UK and in winter these bring very cold air from the Arctic and continental Europe.
Sometimes the polar vortex can even break down entirely, in an event called a ‘Sudden Stratospheric Warming’. This has been linked to many spells of cold winter weather in recent years.
So, changes in the polar vortex in the stratosphere can affect the strength of the jet stream and as a result whether we get milder or colder weather in winter.
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With the jet stream between now and just past mid January 2020 showing that is will track north of Ireland and the UK that will lead to unsettled weather with heavy rain at times and windy weather leading to the possible risk of 1 or 2 storms in that period that could bring some severe and damaging winds. The current AO pattern is also positive which also is another factor along with where the strong Jet stream will be positioned.
That does not mean that cold snaps can not occur this January it just mean that any cold snaps that if they do occur will be brief and only last 1 to 2 days but temperatures would not be severe. Any snow would be mainly across high ground areas and likely come from areas of low pressure moving in from the Atlantic and mixing with any colder air which would be quickly moved away again.
Over the last few week much of the severe cold weather has been over Canada and parts of the USA and this is due to the polar vortex.
Looking at the end of January into February there are signs that the strong westerly flow across Ireland and the UK could ease with pressure building across Europe and Scandinavia but this is rather uncertain yet and if it was to occur then is would weaken the normal westerly flow and could allow colder and drier weather from the east or north to develop.
Kenneth from the Donegal Weather Channel
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