How cold does it have to be for it to snow? The thought that it might be “too cold” also explains when snow forms.

Temperatures will drop to -10 degrees by the end of the week, with snow expected in parts of the country.

This comes after the Met Office and the UK Health Security Agency (UKHSA) issued a severe cold snap warning for England, one notch below a national emergency, and warned that falling temperatures could increase health risks for vulnerable people and disrupt supplies. .

Snow fell in Scotland on Tuesday and is likely to move further south by the end of the week.

Rebecca Sherwin, Deputy Chief Meteorologist for the Met Office, said: “We can expect snow and winter rain throughout the week, especially in coastal areas or higher elevations.

“By the end of the week, there will be severe frosts in some places, and the temperature will drop to -10 degrees at night.”

How cold does it have to be for it to snow?

Many people believe that temperatures must be below freezing for snow to fall, but the Met Office says that’s not the case.

“Precipitation falls like snow when the air temperature is below 2°C. It’s a myth that snow has to be below freezing.”

“The heaviest snow falls here in Germany, even when the air temperature is between 0 and 2°C. Falling snow begins to melt as soon as the temperature rises above freezing, but when the melting process begins, the air around the snowflake cools.”

When the temperature is above 2°C, the snowflake melts and instead of snow falls sleet, and when it is even warmer, it rains.

However, sometimes it can be too cold for snow – or at least too cold for snow to be a possibility.

Matt Perutka, a meteorologist at the US National Weather Service Engineering Lab in Maryland, explains: Scientific American: “For snow to form, there must be moisture in the atmosphere, and very cold air contains very little moisture.

“Once ground temperatures drop below about -20°C, snowfall is unlikely in most places. Therefore, significant snowfalls at such low temperatures rarely occur.

What do we need to make it snow in Britain?

The main components of snowfall are adequate cold air and moisture.

The Met Office explains: “In order for cold air to blow across the UK, we need winds from the north or east. North winds (i.e. air flowing from north to south) carry air directly from the Arctic across the cold sea to Britain. In winter, easterly winds (that is, those that blow from east to west) are cold because they blow from the cold continental hinterland of continental Europe.

“However, the most common wind direction in Britain is the southwest, so we mostly get relatively soft air from the Atlantic, which brings rain, rather than cold air from the north and east, which often turns rain into snow. “

However, there is another way that requires very light winds – high pressure, which lasts a long time in the winter in the UK.

When the skies are clear, temperatures can gradually drop from day to day as the sun is weak and little cloud cover keeps the heat in at night.

The weather bureau adds: “What about humidity? With cold easterly winds and air blowing over such a large area of ​​land, there is often very little moisture to form snow, and instead we get crisp winter sun.

“Either we need cold air to get into the rainy weather front and turn it into snow, or the cold air needs to absorb enough moisture during its short journey across the North Sea to form showers.”

Consideration should also be given to the effect of rising air in hills and mountains. Since it is generally colder higher in the atmosphere, as the air rises up the hill and condenses to form clouds and precipitation, the air becomes colder.

This precipitation will be in the form of rain or snow, depending on how cold the air is and where the “freezing point” is.

This is the part of the atmosphere where the air temperature is 0°C. The meteorological service explains that on some days it can reach 60 meters above sea level.

What is the weather forecast for this week?

Here is the weather forecast for the rest of the week:

Wednesday

Winter showers in northern Scotland, Northern Ireland, Wales and eastern England, snow on northern hills. The rest is mostly sunny but cold.

Wednesday evening

Widespread frost with some icy surfaces. Snow and snow showers are most common in northern Scotland but occasionally affect parts of Northern Ireland, North Wales and East Anglia.

Thursday

Frequent snow showers in northern Scotland could spread to other parts of northern Britain and there is also a risk of winter rain in the far west. Elsewhere it is fresh and cold.

Friday to Sunday

Constantly very cold, in places severe night frosts and in places supercooled fog. Winter showers will mostly hit the coast while many inland areas are dry and sunny.