For the last few weeks we have been bounced from unseasonal warmth to unexpected snow, then back again to warm conditions. It's all a question of where our weather is coming from.

Unseasonably mild weather has been affecting almost all of the country, with only north-west Scotland and Northern Ireland experiencing proper winter chill (though even there it is mainly high winds that are making it feel colder than it is).

The reason our weather is often so unsettled is because of our position between an ocean and a continental land mass. There's always liable to be a battle between Atlantic air and European air to decide which brings us our weather. The recent mild spells have usually been associated with a south-westerly wind, bringing air currents warmed by the waters of the South Atlantic - and they may be even warmer than usual because of El Nino.

The snows of a week or two ago came from arctic winds arriving from the north or over Scandinavia. That gave way to the current warm period as the south-west winds took control again. Now, however, it looks as though westerly winds over the Atlantic will bring a front of cold air, arriving over Britain towards the end of the week. Then we'll get back to the usual December cold and frosty mornings.