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Your interview: Will Lang, chief forecaster at the Met Office
6:00am Saturday 11th January 2014 in News
Q: Are the winds getting stronger and is the rain becoming more frequent?
Will Lang (WL): The jet stream has been particularly strong over the past few weeks – partly due to particularly warm and cold air being squeezed together in the mid-latitudes, where the UK sits.
This could be due to nothing more than the natural variability which governs Atlantic weather.
However, looking at the broader picture, there is one factor which could increase the risk of a stormy start to winter and this is called the |quasi-biennial oscillation (QBO for short).
This is a cycle, discovered by the Met Office in 1959, which involves a narrow band of fast moving winds (much like our jet stream) which sits about 15 miles up over the equator.
The cycle sees these winds flip from easterly to westerly roughly every 14 months.
In 1975 Met Office researchers discovered that when the QBO is in its westerly phase, it tends to increase the westerlies in our own jet stream – meaning there’s a higher risk of a stronger, more persistent jet stream with more vigorous Atlantic storms.
It has been in its westerly phase since early 2013 and we expect it to decline over the next few months.
There has been an overall increase in the average rainfall for Sussex over the past 50 years.
The 30-year average between 1961 and 1990 was 88.2mm annually but the 30-year average between 1981 and 2010 was 94.6mm annually.
However there is a huge variability in UK rainfall so this could be an indication of nothing more than this.
Q: When is it going to stop raining?
WL: We’ll see further rain at times over the next few days, but nothing like what we’ve seen recently.
It’s looking much more like fairly normal winter weather, with some drier, sunnier spells too and some colder nights.
Q: Are long term forecasts really reliable?
WL: At the Met Office we are constantly researching and improving our long range forecasting capacity, |and research has shown great improvements over recent |years.
However, the science does not currently exist when it comes to making |detailed predictions of what the weather will be months |ahead.
In terms of our five-day forecast, we have seen great improvements in accuracy over recent decades – today our forecasts out to four days ahead are as accurate as our one day forecast was 30 years ago.
Q: What is the climate going to be like in Sussex in 20 years time?
WL: There is a resource where you can explore what will happen to the climate in your area. UK Climate Projects gives future climate projections for UK regions and can be found at ukclimateprojections.metoffice.gov.uk/
Q: What’s the difference between a weather event and a climate event? I ask as those who support global warming say the wild weather is evidence but I also heard someone say that the cold snap in the USA was a “weather event” and thus did not contradict global warming.
WL: “Climate” refers to long term averages and trends. If the frequency of “wild” weather events increases over time, then this may be seen as evidence for a longer term climatic change.
But you really have to make this calculation over a very long period of time – usually decades or more – to spot this trend.
It’s really difficult to prove that a single “event”, such as the cold weather in the USA, is directly the result of climate change, but we do expect such unusual weather to become more frequent.
Q: How far in advance can we predict the weather nowadays? What is technology bringing to long-range forecasts?
WL: These days we can usually tell you the weather at your location at a given time, to some accuracy, up to a couple of days ahead.
Beyond that we can probably identify the likely weather for your region, and whether it’ll happen in the morning, afternoon or overnight out to around five days.
Looking further ahead still, things get less certain, and we usually talk in terms of what may happen, rather than what will happen.
It all depends on the weather itself though; some conditions are easier to predict than others.
For longer range forecasting, technology is everything.
And computing power and the sophistication of our weather prediction models is the main reason we’ve seen large advances in forecasting on extended timescales – from a month ahead to decades ahead – in recent years.
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