Great Western Coffee Shop

From The BBC (http://www.bbc.co.uk/news/uk-england-somerset-43199496)

Is it a sea at Weston? Or the Bristol Channel river mouth?

Definitely salt water (with some silt) and very tidal with salt water at low tide mark so I'd say sea.

Generally accepted to be sea and not river mouth, at Weston Super Mare, though I would expect that the proximity of the river and the freshwater flow therefrom would render this bit of sea less salty and more liable to freeze.

Minehead is not far away and has generally very similar weather to WSM, but I have not observed any significant freezing of the sea  here. There IS the odd patch of frozen spray near the high tide mark, but it would be exaggeration to call that frozen sea.

The wind is blowing from due east, so places on west facing coasts like Weston will be experiencing the coldest ground temperatures. Minehead will be getting a slight warming from the wind coming along the Bristol Channel coast. The difference will be very slight, but may be enough to affect whether freezing takes place.

Shouldn't that make the east coast colder, as the wind comes in uninterrupted over the sea?

The river at Truro has totally frozen over just by the Tesco store.

The sea offshore is well above freezing, due to the gulf stream, even now. Land has a limited heat source from below, but on long cold clear nights it can cool, by radiation into the sky, to below freezing. That rarely happens in Britain, as the air flow is mainly off the Atlantic and brings cloud cover that blocks that radiative heat loss.

An easterly can bring cold air across the (relatively cold) continent from where it can make a quick hop across the channel and make Kent very cold. Kent has always had that reputation, though not among those with too short a memory to have seen it. It takes several days of cold easterly airflow to chill the ground to well below freezing, especially later in spring when the clear sky allows the sun to reheat it during the day.

For really cold conditions, you need to do all the above and then stop the airflow, using a big anticyclone. Then the air just sits over you getting colder, and if you're really lucky you get all-day fog (freezing fog, in this case). That cuts the daytime heating and then it can keep getting even colder for several days, at least in places prone to such fog.

Very well put Sir you don't work for the Met office do you ?.

The sea temperature is warmer than the land temperature at this time of year, so no, though this wind has come over a large frozen landmass and then a short hop over the sea, so the difference in temperatures between our east and west coasts won't be much. But it will feel colder on the east coast, because of the windchill factor, and as stated above, after several days of anticyclone, Kent can become very chilled.

I visited Weston today. Didn't see any frozen sea, but the high tide mark was a mix of snow, scum and detritus.

They're not all bad, in fairness, and make a valuable contribution to the local economy...

Some of my best friends live in Weston, so no, that's not what I meant.  :D

I was thinking that this particular mass of air is cold because it's come from Siberia, or Northern Scandinavia, where it's much colder than the British Isles, so surely it should be warming up as it passes over our warmer land? Also, more wind chill when it hits the East Coast unimpeded by lumpy land? Not saying I'm not wrong, just explaining why!

You should have felt it in the middle of the North Sea!

This one was, I hear from the BBC, straight out of Siberia. Our green and pleasant land will have warmed it, but there's been a lot of cold air to try to make a difference too. Not only that, the nights have been clear, meaning no fluffy blanket to keep any warmth in, and the air over the country has been very dry, because cold air doesn't hold as much water vapour as warm air. The brilliant sunshine we have had can't warm the air at all without water (it doesn't do that much anyway) and can only warm the air by warming the ground first, and by the time it has done that, the wind has taken the slightly less cold air away, to be replaced by fresh cold air. The south of England isn't that lumpy, so doesn't have too much of a sheltering effect in extreme conditions, although the ground applies considerable friction to wind, especially at low levels, slowing it by up to 20%. That is part of the reason why winds at different altitudes move at different speeds and in different directions.

Britain is pretty small east-west-wise, so if the air is still in a hurry that doesn't hav a big effect. But what's more important is the heat flow and what helps and hinders it.

Ground isn't good thermal conductor, so while its heat capacity is higher than air (which is so much thinner) only heat in the very top layer can escape quickly. The air, however, can convect, so heat can move upwards with any warmed air which is replaced by more cold stuff. The wind chill effect on heat loss from your bare skin is often described in terms of the wind removing the warm air that you have heated up and replacing it by cold. The same is true of bare ground, but more ground is covered by at least grass, if not trees, crops, buildings, etc. all of which trap air near the ground and so insulate it.

When the air gets to the sea, however, it meets something that has a higher heat capacity than itself or the ground, but can also convect (at least above 4^o). So the sea has far larger heat reserves available for heating the air, it imports heat from the Caribbean, and it lacks insulting stuff. Of course it has waves, but they just encourage mixing - the wind whips spray off their tops. Even if that water falls back quickly, and it's too cold for it to moisten the air much, drops have a huge surface area to heat the air through.

So the preferred route for importing cold air is via Germany and Flanders, but the fine details will always depend on the actual track. And if you stand on the Esplanade in Aberdeen you'll feel cold - but that's just true in general, even in the summer.

So, technically, it then became an Iceland store?  ;)