We often see weather forecasters predicting snowstorms that don't materialise.

Unlike predictions of Storm Emma today forecasts of snow often amount to less than one flake of the white stuff.

It's not because meteorologists are incompetent - they're not - nor is it because they like to frighten us unnecessarily.

It's because snow cannot accurately be predicted more than three days in advance, reports WalesOnline .

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Meteorology is after all an inexact science; a very educated art of guesswork. That's why qualified weather folk always talk of chances of certain types of weather rather than absolutes.

Channel 4 weatherman and presenter Liam Dutton said: "I’ve seen a weather computer model predict six inches of snow five days away for southern England, only six hours later to predict the same area to have nothing – showing just how finely balanced and volatile snow predictions can be."

He added: "The bottom line is that you should never believe a detailed UK snow forecast more than three days ahead.

"Predicting snow in the UK is difficult and weather computer models rarely get it right more than a few days ahead. In some cases, they still get it wrong the day before it happens!"

Snow on roofs in Huddersfield town centre.

Liam points to several conditions, often seemingly minimal, which can make a big difference to how much snow we get. They are:

  • Altitude
  • Air temperature
  • Urban heat
  • Distance from the coast
  • Wind strength and precipitation intensity

"Temperature is probably one of the most crucial factors. As a general rule of thumb, snow in the UK tends to fall when the temperature is 2°C or less."

But, a temperature marginally above 2°C can make sleet or rain more likely. Altitude is also very important. The higher you go, the colder it gets, so snow is much more likely over hills and mountains.

Meanwhile, towns and cities can be slightly warmer than rural areas - so again, the slight difference in air temperature can influence what falls - sleet or snow. With temperatures on the coast also slightly higher than those inland (thanks to the relatively warm water around the UK), snow is also less likely in coastal areas than inland.