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Why forecasting snow is so difficult in the UK

Why forecasting snow is so difficult in the UK
Credit: AI-generated image

Cold winter weather in the UK almost always brings with it talk of snow.

British people tend to approach of snow with a combination of excitement and trepidation. Who doesn't like the sight of unspoiled snow glittering over the rooftops like a Christmas card? But not many people enjoy the aftermath—an ice slush nightmare, soaking up the dirt from our streets and roads.

Forecasting snow is tricky in Britain though. And predictions tend to be uncertain. By the time British people reach adulthood, particularly those who live in southern England, a lot learn to treat forecasts of snow with cynicism. You might go to bed delighted by forecasts of snow only to wake the next day greeted by rain.

The UK's erratic winter is caused by two things: its location and the fact that small differences in can cause dramatic changes to the .

The UK is located right where a number of different global weather systems converge. Unlike many places in the world, freezing weather in Britain is generally accompanied by northerly or easterly winds. But (liquid or frozen water) is usually from the west. Colder weather in the UK makes precipitation less likely. Which is why if we see snow, it often arrives as a light shower or flurry.

Thick snow usually happens when precipitation from the west hits cold air from the east or north.

Don't shoot the messenger

Weather forecasting has come a long way over the last four decades. Improved computing, satellites, transformed communication and have made weather forecasting much more accurate. In 2022, storm Eunice and the summer 40 degrees Celsius heatwave are both examples of how much forecasting has improved. It is not only able to accurately predict "normal" weather, but also when will occur.

Forecasters today can predict widespread precipitation down to the hour. So mapping out is not the problem. The issue is that British winters make it a lot harder to tell what form precipitation will take when it reaches us.

This means predicting whether we will get sleet, freezing rain, snow or just rain. If you watch weather forecasts on a regular basis you will probably have heard the vague phrase "wintry precipitation". This is the forecaster wrangling with an uncertain forecast as the term covers everything from rain to snow.

A lot of the rain that we see in the UK, at all times of year, was snow when it started falling, but has fallen into air that is warmer than 0⁰C and melted. That means when forecasters predict rain, they are often predicting melted snow. If it's 20⁰C in the summer, there is no doubt that by the time the snow reaches the ground it will have turned to rain.

For many places in the world the reverse is true. If the temperature is going to be -10⁰C, it will settle on the ground as snow. Back in 2018, in the UK the Beast from the East brought with it temperatures so low the meteorologists could confidently predict snow.

A headache for weather forecasters

Most of the time, however, UK weather forecasters are working with expected temperatures close to 0 degrees Celsius. In this case a very small change to the temperature totally changes the weather. Weather forecasts tend to be accurate down to a couple of degrees Celsius. But when your baseline is 0 degrees Celsius then a rise of 2⁰C will mean the snow melts and we get rain. But 2⁰C colder and it's just snow. Somewhere in the middle creates sleet.

And this is the other main reason why predicting snow is so hard in the UK. A small difference in temperature makes a really big difference to the outcome.

Precipitation lowers the air temperature. Heavier drops the temperature even more. Heavier sleet turns to . This means that even if the temperature of the system is predicted correctly, the fine details of the rate of precipitation will affect the form. It just so happens that much of the wintry weather in the UK falls at the temperature that makes the outcome sensitive to tiny changes. So, I'm afraid the phrase "wintery " is here to stay.

Provided by The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.The Conversation

Citation: Why forecasting snow is so difficult in the UK (2023, January 24) retrieved 8 December 2023 from
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