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.





Healthy Outlook® – helping patients with COPD this winter.

1 11 2012

Alongside our Cold Weather Alert Service this winter, the Met Office is working with the NHS and Primary Care Trusts (PCTs) to help keep people well at times of severe cold weather with our specially produced Healthy Outlook® service. The service helps patients suffering with Chronic Obstructive Pulmonary Disease (COPD) stay informed about any potential adverse cold weather periods that may have an effect on their well-being. Healthy Outlook® also gives professionals and patients the opportunity to take action by giving them advance warning of colder weather and circulating infections.

COPD is the term used to describe a number of conditions, including chronic bronchitis and emphysema, where people have difficulty breathing because of long-term damage to their lungs. Poor weather conditions, such as extreme cold in winter can exacerbate COPD symptoms and contribute to breathing difficulties which often leads to a spell in hospital for the patient. There are around 30,000 COPD-related deaths each year in the UK and it is the second highest cause of emergency hospital admissions.

Katie Russell, Met Office Business Manager for Health, said: “We are excited to be working with the NHS and GPs surgeries again this year. The Met Office has been involved in COPD Health forecasting for a number of years and feedback from patients shows that 82% found Healthy Outlook® helped them manage their COPD better during periods of cold weather.”

This winter, Healthy Outlook® is also being trialled in-store in selected retail pharmacies to give those suffering from COPD a more flexible method of managing their condition. By signing up to the service through the retail outlets, patients can benefit from COPD forecast alerts even if their local PCT is not involved.

As with the standard service, patients will receive a pack containing advice and tools that can help them to manage their condition.  An automated telephone call to a number of their choice will also alert them to conditions in the environment which are expected to increase the risk of symptoms of COPD becoming worse.

The latest information about the weather and warnings can be found on the Met Office website, iPhone and Android apps and on twitter. Further information on Healthy Outlook can be found on the Met Office’s Cold weather and health web pages.





Coldest temperatures of winter so far

11 02 2012

Last night and today have seen some of the lowest temperatures of the winter so far.

Official observations show Holbeach in Lincolnshire dropped to -15.6 °C overnight, beating the previous coldest temperature of this winter of -12.4 °C at South Newington in Oxfordshire overnight on 3-4 February.

Today has seen also the lowest day-time maximum temperature for the UK so far this winter, with Coningsby in Lincolnshire only getting up to -5.3 °C. The previous record for this winter was -2.8 °C, set at Cassley in Scotland on 15 January.

It’s worth noting that some even lower temperatures have been quoted in the media. However, these are not official Met Office observations.

Our official observation sites conform to rigorous standards set by the World Meteorological Organization (WMO). This includes observation equipment undergoing regular checks and calibration, as well as meeting requirements about the location of the observation site to ensure readings aren’t affected by other factors.

This doesn’t mean readings from non-official sites are wrong, just that they cannot be officially recognised because they are not part of our WMO-approved network.

The reason last night and today have seen these low temperatures comes down to a combination of factors. Cold air from the east is still flooding over parts of the UK. Snow is also still lying in some places, and this can keep temperatures down by acting like an ice pack – as well as reflecting back energy from the Sun. Clear skies and light winds have also played a part, as these factors mean heat can radiate away into the sky.

Looking ahead, tonight is expected to be cold, although it is unlikely to be quite as cold as last night. As we move through next week, temperatures are expected to move closer to or even slightly above average. You can stay up to date with the latest outlook with our forecasts and warnings.

 

Coldest overnight temperatures for 10-11 February

-15.6 °C Holbeach, Lincolnshire

-15.5 °C Cavendish, Suffolk

-15.3 °C Cambridge, Cambridgeshire

-15.2 °C Wainfleet, Lincolnshire

-14.6 °C Santon Downham, Suffolk





Snow brings disruption in the east as ice becomes hazard into next week

5 02 2012
Credit: Marco Anderson

As forecast, an Atlantic weather front pushed across the UK through yesterday and overnight bringing snowfall to many parts of the UK. As expected the worst of the conditions were across the east of the UK, where the cold air from the continent was able to hold on, leading to significant snowfall, especially across South East England, East Anglia, Lincolnshire, parts of the Midlands, Yorkshire, the North East and the southern uplands of Scotland.

Further west, although there was some snow for a time, the milder air, associated with the weather front soon turned the snow to rain, leaving a grey rather than a white start to Sunday.

As the snow and rain moved away, skies cleared allowing it to turn cold again with widespread ice in many conditions. The Met Office still have an Amber warning for icy roads in force at the moment valid until midday today. Overnight lows got to -9.8C at Bramham, -8.9C at Church Fenton, -8.4C at Topcliffe, Dishforth and Leeming, -7.3C at Church Fenton. -7.2C at Linton-on-Ouse and -6.2C at Ravensworth.

The table below shows snow depths recorded at 9 am this morning.

Location Snow Depth ( CM)
Church Fenton 15
Wattisham 15
Marham 14
Conningsby 12
Cranwell 12
Leek, Thorncliffe 11
Herstmonceux 11
Northolt 10
Bingley 10
High Wycombe 9
Wittering 9
Eskdalemuir 8
Waddington 8
Coleshill 7
Heathrow 7
Nottingham, Watnall 7
Charlwood 6
Leconfield 6
Brize Norton 4
Woodford 4
Leeming 4
Loftus 4
Benson 3
Odiham 3
Albemarle 3
Odiham 3
Larkhill 3
Sennybridge 3
Andrewsfield 2
Hereford, Credenhill 2
Middle Wallop 2
Shawbury 1
Manston 1

The band of snow has now cleared the far southeast of England and for the rest of the day it will remain largely dry, but cold in the east, Further west it will turn cloudier with some outbreaks of rain, with some sleet or snow on higher ground. Overnight, cloud and a little rain will slowly spread to many places, although eastern Scotland will probably remain dry. Cold and foggy, especially in areas with lying snow and frosty in the east.

Heading into next week there is only a little snow in the forecast at the moment. Monday will be rather cold with ice likely to be a hazard especially in the southeast. It will then be generally cloudy with only occasional brighter intervals. Patchy rain will affect many areas, this mainly light. It will stay very cold in the east and southeast, but will be less cold elsewhere.





Colder weather on the way

18 11 2010

Following recent spells of wet and windy weather, forecasters at the Met Office are predicting a change to colder conditions as we head through the weekend and into next week.

The change will see the return of overnight frosts and showery rain in many eastern regions of the UK, with a wintry mix over the hills.

Met Office Chief Forecaster, Richard Young said: “Temperatures are expected fall during next week, with eastern parts of the country the most likely to see any wintry weather.”

You can check out the latest weather forecast on our website.








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