December is shaping up to be a month of two halves, according to current weather projections. Dull and dismal conditions are likely to remain in place for a couple of weeks but there are signs this could be replaced by colder weather in the run-up to Christmas.
A short-lived weakening of the polar vortex has leaked Arctic air across North America but it is having little impact over Europe, where conditions are likely to stay mild and wet until mid-December. What happens from there is still open to debate but there are signs it will get colder.
In its long-range forecast, the Met Office said that, between December 15-29, there is a "greater chance of spells of high pressure". With this comes a greater likelihood of overnight frosts and snow on the hills.
In the coming days, a Scandinavian blocking high might develop. But this is more likely to divert low pressure systems further south rather than usher in freezing air from the east.
Netweather meteorologist Ian Simpson said this could change in the second half of December if the Scandinavian high strengthens.
He said: "With some blocking anticyclones looking set to be in place to the north of Britain towards mid-December, especially around Scandinavia, some of the building blocks will be in place to increase the chances of something colder heading in at some point in the second half of December."
Weather models currently show few signs of a dramatic dip in temperatures before December 17. Beyond this, some runs do indicate a change, with lows of -4C in Wales, but at this range it's difficult to be precise. Join the North Wales Live Whatsapp community now
In its ensemble forecasts for the second half of the month, the Met Office is predicting spells of colder weather interspersed with milder conditions.
"The forecaster said: "There is a greater chance of spells of high pressure during this period, bringing more in the way of dry weather compared to the unsettled patterns we are likely to see through the first couple of weeks of December, which also increases the chances of overnight fog and frost.
"There will probably still be some spells of rain, showers, and stronger winds, especially in the west. Hill snow is also a possibility, mainly in the north.
"Overall, near or slightly above average temperatures are most likely, though some colder spells are also possible, especially should any prolonged settled spells develop."
For the past decade, December has been noticeably dull. Last year the month was mild throughout but it followed two cold Decembers: in 2023 there was widespread snow on December 3.
Usually, December is the third coldest month after January and February - though this hierarchy differed in the 1990s and 2000s when December was often the coldest, according to Netweather's Ian Simpson.
He said: "There was a run of years with cold and sometimes snowy weather recurring especially between Christmas and New Year, with widespread white Christmases in 1995, 2009 and 2010. Some areas also saw a white Christmas in 1993, 1996, 1999 and/or 2004."
The coldest of the lot was December 2010 - the coldest since at least 1890. Since then, all winter months have been running about 1C warmer than prior to the 1990s, he added. Sign up for the North Wales Live newsletter sent twice daily to your inbox