What have February and the winter been like so far?

27 02 2013

Provisional figures from the Met Office show that February so far (1 – 25) has been colder and drier than average, while the winter as a whole (December 1 to February 25) looks set to be pretty average.

For February, everywhere is set to have been colder than average with the UK mean temperature currently standing at 2.7 °C. Northern parts have seen the best of the sunshine with Scotland recording 13 % more sunshine than average at 71 hours.

EARLY

mean temperature

sunshine duration

precipitation

1-25 Feb 2013

Actual

Difference from 1981-2010 average

Actual

% of 1981-2010 average

Actual

% of 1981-2010 average

degC

degC

hours

%

mm

%

UK

2.7

-0.9

66.1

95

58.0

65

England

2.9

-1.2

62.9

85

41.0

68

Wales

3.0

-1.0

66.9

95

79.0

71

Scotland

2.2

-0.5

71.0

113

78.2

60

N Ireland

4.0

-0.3

67.1

101

68.9

82

For the winter as a whole, the UK mean temperature of 3.3 °C makes it milder than 2008/09 (3.2 °C), 2009/10 (1.6 °C) and 2010/11 (2.4 °C), but colder than 2011/12 (4.6 °C).

However looking further back 2006/07 and 2007/08 were two very mild winters with UK mean temperatures of 5.6 °C and 4.9 °C respectively. The 2006/07 winter was the second warmest on the national record going back to 1910, behind 1988/89 when the UK mean temperature was 5.8 °C.

EARLY

mean temperature

sunshine duration

precipitation

Winter 2012/2013
(3 days to go)

Actual

Difference from 1981-2010 average

Actual

Percentage of 1981-2010 average

Actual

Percentage of 1981-2010 average

degC

degC

hours

%

mm

%

UK

3.3

-0.4

152.2

96

345.9

105

England

3.6

-0.6

166.9

95

267.4

116

Wales

3.8

-0.4

154.4

96

501.4

116

Scotland

2.5

-0.2

128.7

100

436.5

93

N Ireland

4.2

-0.1

144.3

97

332.3

106

This winter has once again demonstrated how variable the weather in the UK can be. Starting with some mild and wet weather in December and a mild start to January it turned cold from the middle of January with snow affecting many areas at times. The cold weather continued through February which was a dry month.





It’s cold but why is there no frost?

25 02 2013

There’s no denying that we have seen some cold weather this winter with plenty of frost, ice and in many cases, snow. However, the last week has been cold – arguably perhaps feeling colder than any other time this winter – but we haven’t seen any evidence of this on the ground in the way of frost. So how is this possible?

For a classic frosty night we need a few ingredients: low temperatures, clear skies, calm winds and moisture. A clear, calm night gives excellent radiation conditions – by this we mean that the heat absorbed by the Earth’s surface during the day escapes readily back into space and allows temperatures to fall. If the temperature falls to the dew point (the temperature to which air must cool for it to become saturated with water vapour) moisture will condense and form droplets on the ground’s surface. When temperatures fall below freezing the droplets freeze and we get frost.

So what about the last few days? They have been cold but there hasn’t really been any prolonged or hard frost. How come? Well, much of Scotland and Northern Ireland has had the required ingredients and been frosty, but the rest of the UK has only had low temperatures. Much of England and Wales have seen a fair amount of cloud and some brisk winds.

25th Feb 2013 crop

Surface pressure chart from 25 February 2013

Cloud acts as a blanket and although temperatures have fallen during the night-time, cloud cover has stopped them falling well below freezing and therefore made it difficult for a thick frost to form. The wind is also important as it mixes the lower part of our atmosphere. Rather than having cold air pooling in one place and causing low temperatures, the wind can bring less cold air from another location or even bring it down from the upper atmosphere. This also helps to keep temperatures from falling too low. However, easterly winds this week have certainly made it feel very cold indeed!

25 Feb vis pic

Visible satellite image from 25 February 2013

Lastly, the air near the surface has been relatively dry. This is important because it means the temperature of the air must fall very low in order to reach its dew point. The cloud and wind has stopped this from happening easily and therefore reduced the risk of frost.

Cold weather, then, brings lots of different tastes of winter, especially to the UK, and we have seen nearly all of them this season. More information on all types of weather can be found here.





Why does it feel so cold? A guide to ‘feels like’ temperatures

24 02 2013

With bitterly cold conditions across parts of the UK just now, have you been asking yourself why it can feel so much colder in the wind?

The temperatures that you normally see on our website represent the temperature of the air, but this takes no account of how we actually experience the temperature. It is our ‘feels like’ temperature that gives you a better idea about how the weather will actually feel when you step outdoors.

Our ‘feels like’ temperature takes into account wind speeds and humidity to assess how the human body actually feels temperature.  For example in winter a strong wind can feel much colder than the measured temperature would indicate. The impacts of the temperature and wind combined can be much greater  than each on their own and the feels like temperature allows users to make a better assessment of conditions outdoors.

But how do you actually calculate the ‘feels like’ temperature?

We calculate a ‘feels like temperature by taking into account the expected air temperature, relative humidity and the strength of the wind at around 5 feet (the typical height of an human face) combined with our understanding of how heat is lost from the human body during cold and windy days.

On windy days the speed of moisture evaporation from your skin increases and serves to move heat away from your body making it feel colder than it actually is. The exception to this rule, however, is when higher temperatures are concerned. At higher temperatures, wind chill is considered far less significant. Instead humidity plays a greater role. When a human being perspires, the water in his or her sweat evaporates. This results in the cooling of the body as heat is carried away from it. When humidity is high, the rate of evaporation and cooling is reduced, resulting in it feeling hotter than it actually is.

Using these facts we use a formula to adjust the air temperature based on our understanding of wind chill at lower temperatures, heat index at higher temperatures and a combination of the two in between.

You can get ‘feels like’ temperatures on our five day forecast and on our Android, iPhone and Windows Phone apps.





Cold weather across UK

22 02 2013

The start of this week was relatively mild and sunny but we have seen a change to colder and cloudier weather during the course of the week.

20081219_frost_fog

High pressure became established to the north-east of the UK and this dragged in colder air from Scandinavia. It took some time for the cold air to filter across the whole of the UK but over the last couple of days daytime temperatures struggled to rise to 3 °C in some places. Brisk winds across England and Wales made it feel much colder, and we saw a few snow showers across eastern parts of the country.

Will Lang, Met Office Chief Forecaster, said: “This is a different taste of winter to the snow and ice we have seen of late. These largely dry, settled and cold conditions may not be as disruptive to travel but they do present concerns surrounding the health and well being of the elderly and vulnerable.”

The Met Office issued a level 3 Cold Weather Alert in light of the widespread and prolonged cold conditions. These alerts give advance warning of adverse weather conditions, which enable people to take extra precautions to keep safe and well.

A Department of Health spokesperson said: “Severe cold weather can be dangerous, especially for the very young or very old or those with chronic disease. You can find advice on how to reduce your risk or that of somebody you know on the NHS Choices website, ringing NHS Direct on 0845 46 47 or contacting your local GP or pharmacist.

“The NHS is well prepared for the winter and we are providing an extra £330 million to the NHS and social care services to help cope with the added pressure that the winter brings.”

With high pressure remaining in place, cold and largely settled weather looks set to remain across the UK until the end of February at least, and you can find the latest information from our forecasts and warnings, our mobile apps and through broadcasts on TV and radio.





Top ten romantic weather phenomena

12 02 2013

With Valentine’s day this week, we’ve complied the top ten romantic or magical weather conditions.

1. Diamond dust – Diamond dust consists of extremely small ice crystals, usually formed at temperatures below -30 °C. The name diamond dust comes from the sparkling effect created when light reflects on the ice crystals in the air.
2. Sunset – Sunsets are colourful because the light from the setting sun has to travel through more of the atmosphere to reach us. This means more of the blue light from the sun is scattered away from us, so we can see more of the red light.
3. Crepuscular rays – This phenomenon occurs when light from the rising or setting sun is scattered, producing sunbeams.
4. Iridescent clouds – A pretty display of iridescent colours in a cloud is most commonly seen in high level cumulus clouds.
5. Dew – Very small droplets of water which form during calm weather as the air cools. The process of droplets settling is called ‘dew-fall’.
6. FrostFrost forms on still, clear and cold nights. The cool air causes water vapour in the air to condense and form droplets. When the temperature of the ground or surface is below 0 °C the moisture freezes into ice crystals.
7. Double rainbow – Magical as they may seem, a double rainbow occurs when a secondary rainbow forms outside of the brighter, primary rainbow. The colour sequence is reversed because the light has been reflected within each raindrop a second time. As the light has been refracted twice, the secondary rainbow will not be as bright.
8. Snowflakes – Every single snowflake is unique, but because molecules in the ice crystals that make up snowflakes join together in a hexagonal structure they always have six sides.
9. Heart shape cloudsClouds can form in virtually any shape, and sometimes you may see some that look like things, even hearts.
10. Halo – A halo can appear around the sun or the moon, and although they may look angelic, can often signify that a weather front is approaching.





Will the UK see snow this weekend?

8 02 2013

There is potential for some significant amounts of snow over parts of the UK later this weekend. However, the detail of where and when this snow will fall is still uncertain.

So what is happening in the atmosphere? A frontal system that’s been working its way across the Atlantic during the last couple of days will push rather erratically eastwards across the UK this weekend, bringing some persistent and, at times, heavy rain to parts of the country. We also currently have some cold air sitting over the near continent and, as the rain advances eastwards, an area of low pressure will form over southern parts of the UK, causing winds to turn easterly and bring this colder air in from the continent.

How and where this area of low pressure forms will also be critical in determining where and when the heaviest of the snow falls, and exactly where the dividing line between rain, sleet and snow is.

The most likely scenario at present shows the heaviest snow across the Midlands, Wales and northern England with over 10 cm of snow currently forecast.

However, different computer models are currently showing this process taking place in different ways and in different locations, and it is uncertainty within the atmosphere that is making the Chief Forecasters job so difficult. To help us provide the best advice possible to you, the Met Office uses both deterministic forecast and ensemble forecast models.

A deterministic forecast uses current observations of the atmosphere to create a single forecast. In the case of this weekend’s weather it indicated the most likely place to see snow. However, over the last few days the most likely part of the UK has changed each day which in itself generates lower confidence in the detail of the forecast. To help increase confidence, we use an ensemble model which generates a group of forecasts each with slightly different starting conditions. The Met Office ensemble model has 24 solutions and the output of this model shows the spread in probability of where in the UK could see snow. This highest probability is the point where the majority of the 24 solutions are in agreement. This can be combined with the deterministic forecast to help make a final decision on forecasts and warnings.

Met Office forecasters will continue to look at the available evidence with a view to providing the most accurate, timely, warnings and forecasts.





January weather – your pictures

7 02 2013

Thank you for sharing your January weather pictures with us on Twitter. Here’s a selection of our favourites. The January summary video is coming shortly.





Latest snow depths and wind speeds – 5 February

5 02 2013

As forecast, unsettled wintry conditions brought snow and strong winds to parts of the UK overnight and this morning.

Eskdalemuir saw the deepest snow, with 14 cm of snow recorded at 10 am this morning, while Aviemore recorded 12 cm.

Many areas also saw strong winds, with a gust of 78 mph recorded at Culdrose, Cornwall and 99 mph recorded at Cairngorm Summit.

Snow depths at 10 am 5 February

TIME SITE NAME AREA ELEVATION SNOW DEPTH ( CM)
10:00 ESKDALEMUIR DUMFRIESSHIRE 236 14
10:00 AVIEMORE INVERNESS-SHIRE 228 12
10:00 DRUMALBIN LANARKSHIRE 245 10
10:00 GLENANNE ARMAGH 161 9
10:00 TULLOCH BRIDGE INVERNESS-SHIRE 249 7
10:00 REDESDALE CAMP NORTHUMBERLAND 211 7
10:00 BALLYPATRICK FOREST ANTRIM 156 5
10:00 SPADEADAM CUMBRIA 285 5
10:00 THOMASTOWN FERMANAGH 72 3
10:00 BINGLEY WEST YORKSHIRE 262 2
10:00 ALBEMARLE NORTHUMBERLAND 142 2
10:00 WADDINGTON LINCOLNSHIRE 68 1
10:00 SHAWBURY SHROPSHIRE 72 1

Maximum gust speeds 5 February

TIME SITE NAME AREA ELEVATION MAX GUST SPEED (mph)
00:00 CULDROSE CORNWALL 76 78
04:00 SCILLY ST MARYS AIRPORT ISLES OF SCILLY 31 75
00:00 CHIVENOR DEVON 6 67
03:00 ISLE OF PORTLAND DORSET 52 66
04:00 JERSEY AIRPORT JERSEY 84 66
03:00 GUERNSEY AIRPORT GUERNSEY 101 64
00:00 CAMBORNE CORNWALL 86.85 62
02:00 SOUTHAMPTON, OCEANOGRAPHY CENTRE HAMPSHIRE 26 62
01:00 SOUTH UIST RANGE WESTERN ISLES 4 62
00:00 AVONMOUTH AVON 9 62
00:00 CARDINHAM, BODMIN CORNWALL 200 61
01:00 TIREE ARGYLL 9 60
03:00 WIGHT: ST CATHERINES POINT ISLE OF WIGHT 20 60
01:00 WIGHT: NEEDLES OLD BATTERY ISLE OF WIGHT 80 60
02:00 YEOVILTON SOMERSET 20 60
01:00 CAPEL CURIG GWYNEDD 216 59
01:00 ABERDARON GWYNEDD 95 59
04:00 ISLAY: PORT ELLEN ARGYLL 17 58
01:00 LERWICK SHETLAND 82 58
00:00 MUMBLES HEAD WEST GLAMORGAN 43 56
01:00 ODIHAM HAMPSHIRE 118 56

Maximum gust speeds – mountain sites

TIME SITE NAME AREA ELEVATION MAX GUST SPEED (mph)
09:00 CAIRNGORM SUMMIT INVERNESS-SHIRE 1237 99
07:00 CAIRNWELL ABERDEENSHIRE 928 86
08:00 AONACH MOR INVERNESS-SHIRE 1130 75
09:00 BEALACH NA BA ROSS & CROMARTY 773 67
04:00 GREAT DUN FELL CUMBRIA 847 56
10:00 GLEN OGLE PERTHSHIRE 564 54

Warnings for ice, snow and wind remain in place in some areas.








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