UKC

Above or below freezing to snow

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 Russell Lovett 22 Jan 2014
Have heared people say the temps gone up so we might get some snow have also heared on the weather forcast it has to be above freezing for it to snow so l was thinking if it was above freezing surly it would fall as rain also if it has to be above freezing to snow how come it snows in the Arctic or does it all depend on what kind of snow it is the wet suff we get or the gawple they gey abroad. Just wondering im sure someone out there will know
 crayefish 22 Jan 2014
In reply to Russell Lovett:

> heared on the weather forcast it has to be above freezing for it to snow

Seems to be no problem with snow falling in the Antarctic...

 Mike-W-99 22 Jan 2014
In reply to crayefish:

It hardly ever snows in the worlds largest desert.
 crayefish 22 Jan 2014
In reply to Mike_Watson_99:

Little snow in the interior, but plenty around the coast.
 Dan Arkle 22 Jan 2014

There is no clear answer to this, but...

If the air is really really cold there is hardly any moisture in it - so little snow.

If it is just above zero at ground level, then temps up in the clouds are likely to be well below zero, so snow can fall, although it may melt quickly.

When warm(ish) air with lots of moisture in it comes into contact with very cold air, you are likely to get the biggest dumps.
Cold fronts tend to produce more than warm fronts.
 alooker 22 Jan 2014
In reply to Russell Lovett:

Think I read somewhere once that the heaviest UK snowfall is between 0-2degC. Also it doesn't need to be above freezing to snow, was this ITV weather..? It doesn't snow much in Antarctica because the humidity is so low, as you move out to the coast this changes so you get more snow.

Snow can fall above freeing because as it starts to melt it cools the air surrounding it by evaporative cooling (I think that's the term). This means you can get snow to about 4-5degC. Hail is denser and falls much more quickly, that's why hail can sometimes fall in a summer storm higher than 5deg.
 Misha 22 Jan 2014
In reply to Russell Lovett:
Judging by being in a car and going through rain/slush/snow and back a few times, it snows up to about +2C as others have said. Don't think I've ever seen it snow at +4 or 5 C. It does snow below freezing as well but in practice in the UK it normally snows around the zero mark, as others have said.
 nufkin 22 Jan 2014
In reply to Russell Lovett:

I think I read somewhere that almost all rain starts out as snow, then melts on the way down. Not sure if it's true or not, and it doesn't answer your question, but I just thought it was an interesting titbit
 Webster 22 Jan 2014
In reply to nufkin:
> (In reply to Russell Lovett)
>
> I think I read somewhere that almost all rain starts out as snow, then melts on the way down. Not sure if it's true or not, and it doesn't answer your question, but I just thought it was an interesting titbit

at the latitude of the Uk yes you are correct
 crayefish 22 Jan 2014
In reply to Webster:

Even the heaviest of rain? Those drops are pretty large (too large for a snowflake) and I'd be surprised if it was all through coalescence during falling.

Though I am sure the starting mechanism is the same (seed around which ice forms).
 Trangia 22 Jan 2014
In reply to crayefish:

> Seems to be no problem with snow falling in the Antarctic...

Actually the snowfall is low. IIRC is a designated "desert" area. Most of the snow there is wind blown accumulative rather than fresh snow from precipitation.
 crayefish 22 Jan 2014
In reply to Trangia:

> Actually the snowfall is low. IIRC is a designated "desert" area. Most of the snow there is wind blown accumulative rather than fresh snow from precipitation.

Yes I know... I was just making a point that snow CAN form at very cold temperatures. I wasn't commenting on the quantity. And around the coastal regions of the continent the precipitation level (almost all snow) is reasonably high. Something has to feed those glaciers!
 Michael Gordon 22 Jan 2014
In reply to nufkin:

> I think I read somewhere that almost all rain starts out as snow, then melts on the way down.

Clearly nonsense. A lot of the time the clouds are not that high.

 Milesy 22 Jan 2014
In reply to Michael Gordon:

Especially when you're at 3000ft, in the rain clouds and is 10c....
 duchessofmalfi 22 Jan 2014

The temperature often rises when it snows but it isn't magic.

This can occur when clear skies are followed by cloudy skies. The clear skies lead to cold conditions but, obviously, a lack of falling snow. In order to snow there must be clouds and cloud cover can result in warmer temperatures. This gets a bit mixed up in people's memories resulting in the notions "too cold to snow" (no clouds).
 Webster 23 Jan 2014
In reply to crayefish:

Yeh, ok not always but mostly yes, granted not if the cloud is really low, but generally if the cloud base is low ice crystals will still be forming at the top and melting before they leave the cloud, growing in size all the time
 crayefish 23 Jan 2014
In reply to Webster:

> but generally if the cloud base is low ice crystals will still be forming at the top and melting before they leave the cloud, growing in size all the time

Yeah that's a very good point.
Removed User 23 Jan 2014
In reply to Russell Lovett:

Well, if its any help it snowed here at -20 last week but it does generally "warm" up a bit before it snows. It definitely stays below freezing though.

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