Any signs of a cold snap on the way?
During the last week or so, I’ve had quite a few people asking me on Twitter if there is a cold spell on the way. Interest in this topic always tends to increase at this time of year – largely due to speculative headlines in newspapers and the fact that Christmas is drawing ever closer.
What this blog isn’t going to do is look at the weather for the whole winter, the reasons for which I’ll come to a bit later. However, what it will do is look at the coming weeks and give an idea of the most likely weather that we can expect.
As always, November is a time of year that can experience a huge range of weather as the transitional season autumn takes place, where the northern hemisphere slides from summer into the depths of winter.
November can therefore experience bursts of warmth, often referred to as an Indian summer, or deep cold with the first snows of the season.
However, November this year has been neither so far, with the weather fairly benign for a month that often proves one of the most entertaining in the calendar.
For the next seven to ten days, the jet stream will generally remain to the south of the UK. At first, it won’t be moving very quickly, but it will tend to pick up speed as next week progresses.
As well as picking up speed, it will move even further southwards, so that by the end of next week, it will be sitting across southern parts of Spain and Portugal.
These factors mean that our weather for the next week or so will remain unsettled, with low pressure sitting over us, bringing showers or longer spells of rain.
In fact the same area of low pressure could be over the UK for quite some time. This is because the jet stream that would normally act as a conveyor belt and move it along leaves it behind as it dives southwards across Spain and Portugal.
As a result, area of low pressure will just sit over us and spin around, giving unsettled weather until it slowly weakens.
The following week will then see the jet stream move to the north of the UK, which will encourage high pressure to build and give a change to more settled weather.
However, at the moment, there is some uncertainty as to the orientation of the area of high pressure, which would in turn affect the wind direction and the warmth of the air drawn towards the UK.
With low pressure expected to be the dominant weather feature for the next seven to ten days, all parts of the UK will see outbreaks of rain at times – some of which could be heavy with a risk of localised flooding.
However, as high pressure builds the following week, amounts of rainfall are expected to fall considerably, with many places largely dry with no more than a few showers.
For the next seven to ten days, temperatures generally look to be close to where they should be for this time of year at around 7-12C.
Whilst there is a trend to something a little bit colder that this at the end of this month and into December, at this stage, nothing extreme looks likely – so chilly rather than very cold.
However, as I mentioned a little earlier, there is some uncertainty with the orientation of the high pressure which makes the expected temperatures open to some uncertainty.
Seasonal winter forecasts
Seasonal forecasting is still in its infancy in terms of confidence and reliability. That is why when seasonal predictions are made they often come with a percentage chance of each particular outcome happening, as well as some accompanying comments.
Unfortunately, when these seasonal forecasts are mentioned in the media, these accompanying comments aren’t always included. Therefore, they are easily misunderstood and can given a wrong impression when things don’t turn out as people expect.
Also, seasonal forecasts aim to give a trend of the bigger picture of whether it’s likely to be wetter, drier, colder or warm than normal over a period of three months.
What they don’t set out to do is say that on a particular day in January, it will be 3C with snow showers, which is where the common misconception can lie.
If you think about it, you could have a month where the first two weeks are wetter and milder than normal and the last two weeks colder and drier than normal.
So, although the weather may have been considered extreme when taking each two week period separately, when taking the month as a whole, the extremes would cancel each other out and it would appear to be an average month statistically.