´óÏó´«Ã½

It may have warmed-up recently but we're not completely out of the woods yet as far as snow is concerned.

More rain is on the way this week but Wednesday is a bit more tricky with a mixture of rain and snow expected. Deciding on who gets the snow and how much is the difficult bit.

I don't think everywhere will get snow, and I'm not expecting as much as last week but it's worth keeping an eye on the forecast

So the battle lines between the cold and warm air are being drawn again.

At the moment, we have warm air over us but the cold air isn't too far away over northern Europe and Scandinavia and it's going to move westwards flowing into Britain by the middle of this week.

At the same time, a front will move in from the Atlantic on Wednesday and as it bumps up against the cold air it brings the risk of some snow.

You often here forecasters (including me) talking of rain turning to snow but technically this is wrong. Rain never turns to snow but snow often turns to rain.

In fact much of the rain that falls in Britain starts off as snow, even in the summer, because the temperature at cloud-level is often below freezing.

As the snow falls through the air beneath the cloud the temperature rises, so the snowflakes begin to melt and turn to raindrops.

When we think of rain turning to snow it is because the air under the cloud is getting colder for one reason or another.

So instead of the snow turning to rain as it falls, it remains as snow all the way down from cloud to ground. This can happen in three ways:

1. By colder air flowing in from elsewhere lowering the temperature
2. By raindrops evaporating. This causes cooling as they change from liquid to vapour
3. By snow melting. This causes cooling as the snowflakes change from solid to liquid

So on a winter's day if may be raining with a temperature of 6 Celsius but if the precipitation is heavy and prolonged enough with light winds this can lower the freezing level with more and more snow flakes appearing as the temperature drops.

This will be the case tomorrow with some colder air being imported into Wales helping the process along.

Based on the latest information, it looks like most of the snow on Wednesday will fall in Mid, South and East Wales. Mainly on the higher ground but some low ground could also see a little snow.

As far as amounts are concerned, the latest ideas are 2 to 5 cm in places, 1 to 2 inches. 10cm on high ground above about 200 metres or 650 feet which includes the South Wales Valleys.

Mostly rain on the coast. The rain and snow easing and dying out on Wednesday afternoon.

Beyond that, the cold snap looks like being short-lived. Milder air will take control again later on Thursday with a spell of heavy rain rain and strong winds bringing a risk of localised flooding.

However, I wouldn't be surprised if the cold air has another swipe at us next week and in February with further snowfalls.

We may have see the worst of the white stuff for now but I have a feeling that this winter could be one many of us remember for many years to come...

Derek