Visible satellite image of triple lows over the UK

14 05 2013

This visible satellite and rainfall radar image shows the three areas of low pressure affecting the UK today.

satellite and rain 14 May 2013

We can see three low pressure areas showing up as swirls of cloud to the north of Scotland near Shetland, north of Northern Ireland and off south-west England. The centre of the lows show up as cloud free areas.

The low to the south west has developed quickly through today and will bring strong winds this evening to parts of Cornwall.

Keep up to date with forecasts and warnings for your local area on our website.





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.





Nacreous or ‘mother of pearl’ cloud sightings

10 12 2012

Yesterday there was several sightings of an iridescent cloud in Scotland shared with us on Twitter and Facebook.

As we did not observe the cloud ourselves and are only seeing the pictures, it’s not possible to be 100% certain, however it is most likely that these are nacreous clouds, also known as mother of pearl clouds.

This eye-catching cloud is rarely seen, and has only been sighted in polar regions (such as Scotland and Norway) in the winter months, especially when there is a low over northern Scandinavia with a strong west/north-westerly wind blowing over Scotland. They only form in the lower stratosphere – around 15 miles up – when temperatures here are below -78 °C.

Although nacreous clouds are brightest when the sun is just below the horizon, illuminating them from below, they can also still be seen several hours after the sun has gone down.

Have you seen any interesting weather phenomenons lately? Add your pictures to our Facebook page or tweet them to us @metoffice.

Visit our website for more information on cloud spotting.





Cloud spotting infographic and video

17 01 2012

Having trouble telling a cumulus from a stratus cloud? In our video James Chubb explains how clouds form and how this can help you can tell one cloud from another. We’ve also put together a guide to identifying all the different cloud types and how clouds form on the Met Office website.

To help with observing clouds we’ve created this infographic. Feel free to share and use on your own website or blog, you can get the embed code and a printable version from our cloud spotting page.

Met Office guide to cloud types and pronunciations
Source: metoffice.gov.uk

If you spot any interesting clouds, why not take a picture and add them to our Flickr clouds group.








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