Brief cold snap this weekend

20 11 2015

It will turn cold as we head into the weekend, courtesy of an arctic maritime airmass spreading across the country from the north. Yellow ‘be aware’ National Severe Weather Warnings have been issued for a risk of impacts as a result of both snow and wind. Keep up to date with the weather for your area using our forecast pages.

Cold air spreading southwards during Friday will result in showers turning to snow over high ground in the north of the UK and increasingly to lower levels towards Friday evening as an area of rain, sleet and snow moves southwards. Northern and eastern Scotland and perhaps the northeast of England could see accumulations of 1-4cm in places at low levels, whereas above around 150m 5-10cm could accumulate.

Other areas of the UK could see some snow Friday night into Saturday as the band of rain, sleet and snow transfers southwards with perhaps some small amounts of settling snow over high ground.

The combination of rain, sleet and snow and dropping temperatures will also lead to a risk of ice in places, particularly over high level routes on Saturday morning.

Strong to gale force north or northwesterly winds are also likely Friday night and Saturday which will enhance the cold feel in what will be the coldest air of the season so far. There is a risk of severe gales with gusts of 60-70mph for a time in the most exposed locations over higher routes and along the east and west coasts of the UK.

On Saturday, wintry showers will become confined to parts of Scotland and to eastern and western coastal counties with plenty of sunshine elsewhere. It will feel cold in marked contrast to the recent mild weather and the second mildest start to November on record. Maximum temperatures by day will be 3-7 degrees Celsius but the wind will make it feel much colder. Overnight, minimum temperatures are likely to drop below freezing away from coasts, to give widespread frosts, with the risk of some icy patches where showers have fallen during the day.

Sat Feel 20th Sat Temps 20th










Chief Operational Meteorologist Frank Saunders said: “The Met Office is forecasting strong winds and some snow for this weekend which means there is the likelihood of some difficult driving conditions and possible disruption to transport. With this in mind, if you have travel plans over the weekend, we’d advise that you keep an eye on the forecast and warnings for your area.”

Although this will be the first widespread cold spell of the season, it is fairly typical for mid-late November and it’s not unusual to see snow to lower levels in the north of the UK in late autumn. In recent years the most notable snow event was in late November 2010 when there was lying snow across parts of northern and eastern Britain.

This cold spell will be fairly short-lived with temperatures expected to return to more typical values for the time of year early next week with the weather remaining unsettled.

Why are we now seeing colder weather across the UK?

16 01 2015

Over recent weeks, we have spoken about the very strong jet stream across the Atlantic, driving areas of intense low pressure towards the UK. This has bought spells of very wet, windy but relatively mild conditions to the country.

As many of you would have noticed, although the wind and heavy rain has eased, there is now a colder feel to the weather, both by day and night. But what has caused this change in the weather?

Once again the change is down to the jet stream. It has weakened and its track has moved further south, keeping the deep low pressure systems away from our shores. However, now the UK is to the north of the jet stream we are on its cold side, and this has allowed colder weather to feed in across the country.

Current jet stream

Current jet stream across the Atlantic

So what does this mean for us?

As we look ahead into the weekend and next week, the cold weather looks likely to continue. Daytime temperatures will be near or below average and there will be some frosty nights, as temperatures fall below freezing in many areas. We’ll see some sunny spells around and there will also be showers or longer spells of precipitation in places, giving a mixture of rain, hail, sleet or snow, which may settle in some areas.

Because of the threat of wintry weather over the coming days, we encourage everyone to keep up to date with the latest forecasts and national severe weather warnings and to stay weather aware this winter by following the Met Office on Twitter, Facebook, Google+ and YouTube for the latest weather information. You can find information about how to prepare for every aspect of the winter season at Get Ready for Winter.

As we head towards the latter part of the month, we can see some indications that milder weather may return, but there is considerable uncertainty about this so far in advance.

How do we measure snow?

6 11 2012

Here at the Met Office, we’re already being asked if it’s going to be a White Christmas and there’s always a lot of interest in snow.

It’s too early to give forecasts that far ahead, forecasting snow is – after all – a challenge which requires detailed information. While forecasting snow is one challenge, measuring it when it’s on the ground poses another.

There are several reasons for this. First of all snow is subject to the vagaries of the wind and can be blown into deep drifts, leaving bald patches of earth nearby.

Snow also melts, refreezes, and new snow can fall on top. This makes it difficult to discern how much snow has fallen at different times or on different days.

Another tricky aspect of measuring snow is that it often falls on high ground, away from where the majority of the UK population live – and also away from our observation sites.

Snow often falls on high ground but is less common closer to sea-level.

So what do we do to measure this problematic precipitation? In days gone by a manual observer (ie a human being) would go out with a ruler and measure snow on a flat surface.

But this is time consuming, limits observations (as there were relatively few manual observers) and, apparently, became a tricky operation when snow got particularly deep!

So modern technology has given us automated snow sensors which measure snow depth with a laser signal. A piece of artificial turf is the preferred surface below the laser, as it doesn’t grow and therefore doesn’t complicate readings as grass might.

It’s not all that simple though, as even artificial turf can expand and contract according to temperature, as can the soil below it (which can push the artificial turf up or down). Moles can also cause the same problem! To tackle this, our network is under continual review and calibration to make it as accurate as possible.

These fairly technical pieces of kit can’t be placed everywhere, and until last year there were less than 50 spread out across the UK.

Snow depth sensor

This year we have extended our network with 21 new snow sensors, bringing the total up to 68 – you can see the full network on the map below.

Map showing snow sensor network in 2012

This means we can get snow readings from a wider range of locations, which can help our forecasting and is useful for building records and statistics about UK climate.

It’s worth pointing out that while these additions to our observation network are a valuable step forward, the snow sensor network is still relatively sparse in comparison to our UK land weather observation network, which has 463 stations.

Fortunately this is supplemented by observations supplied to the Weather Observations Website (WOW), where anyone can give an up to date measurement of snow or even upload a picture of how much snow they have.

The very nature of our weather here in the UK means that it’s not possible to give precise information for every location in the country, but our network is being continually improved to provide the most detailed, accurate and up-to-date information available.

You can read more about snow and snow forecasts on our dedicated snow pages.


Get every new post delivered to your Inbox.

Join 7,851 other followers

%d bloggers like this: