Much colder and unsettled weather on the way, with a risk of snow and frost

It's been unusually dry, mild and dull so far this November, thanks to high pressure nearby or over the UK bringing anticyclonic gloom. The first 13 days of this month have been very sunless, with only 16% of the whole month average across SE England and East Anglia with more than a third of the month already gone, the average would be around 35%. Also the UK has also had its driest start to the month on record, in a series which dates back to 1891, with only around 3% of the long-term average for the whole of the month having fallen, some places 1 to 2%. 

% of the monthly average sunshine so far (data from Starling Roost Weather)

% of montly average rainfall so far (data from Starling Roost Weather)

High pressure continues to dominate this week, so it will remain mostly dry and settled with many places seeing more in the way of sunshine this week, with temperatures remaining mild. But it is expected to turn significantly colder at the beginning of next week, as winds turn northerly, bringing cold arctic air across all of the UK, with temperatures remaining well-below-average through much of next week.

The change to colder but also more unsettled conditions takes place this weekend, as a ridge of high pressure over southern Britain to end this week gets squeezed away by an upper trough moving southeast from Greenland into Scandinavia and northern mainland Europe over the weekend and into next week, while a blocking high builds in over Greenland.

This means winds will turn northwesterly or northerly intially across Scotland on Sunday and Monday, then all parts from Tuesday bringing cold air in from the arctic, the air becoming cold enough for snow to fall from increasingly wintry showers over higher ground initially, but increasingly to low-levels through the week.

Cold air from the arctic arrives on Sunday across Scotland, sleet and snow showers arriving too across the north, though settling confined to high ground initially, before falling increasingly to lower levels overnight and further south through Monday as the cold air digs in further south. Most of the showers affecting windwards coasts, drier and sunnier inland. 

Further south, a milder, cloudier and damper picture with outbreaks of rain at times across England and Wales on Sunday, as Atlantic fronts move southeast. Then on Monday, a great deal of uncertainty over the potential for an area of low pressure to cross England and Wales later in the day. Cold arctic air will start to filter down from Scotland during the day following a cold front clearing southeast, so colder and brighter for a time, but GFS and ECMWF show a deepening area of low pressure moving southeast off the Atlantic across England and Wales later in the day. As the rain associated with the low bumps into the cold arctic air spreading down from the north Monday evening and night, it will likely to turn to snow, more especially over higher ground, but perhaps to lower levels after dark if precipitation is heavy enough. But there is a great deal of uncertainty over the track and depth of this low, as is usual at 5+ days out. Any snow falling in association with this low will be transitory, with accumulations temporary away from higher ground in the north. But we will keep an eye on the track of this low on Monday into early Tuesday and update on where may see snow when the models settle on the track.

4 models mslp for Tueday 00z

The low that moves southeast across the UK later on Monday develops in quite complex interactions of jet stream and cold air adevction along a baroclinic zone upstream over the far north Atlantic just south of Greenland. A split strong jet stream moving southeast and shortwave cold trough moving off southern Greenland will help a low to develop along the baroclinic zone separating cold arctic air and milder tropical maritime air to the south. The low moves southeast into the left exit of a strengthening jet streak that moves around an increasingly diffluent upper trough extending southeast into northern Europe, so the low will deepen as it approaches the UK on Monday. But when and how much it deepens is open to question. ICON deepens it earlier than the other models, so the low tracks further north over northern Britain, while GFS and ECMWF deepen the low later, so the low tracks further south over southern Britain.

Then from Tuesday, rain, sleet and snow looks to clear east over the North Sea and near continent first thing Tuesday, followed by a bitterly cold northerly wind for much of the rest of the week, which will blow in wintry showers across northern Scotland and down across windwards coastal areas of the east and west. Mostly dry and sunny inland, though the odd wintry shower may make it through from the north. Snow may fall in heavier showers, even to lower levels, but settling confined to high ground above 250m during the day, but snow may settle at lower levels after dark. Widespread overnight frost is likely where skies clear, which will be likely away from showers near coasts.

There is potential for one or two troughs moving south to bring more organised sleet and snow for the rest of the week, but these can't be pin-pointed with any accuracy this far out. Also, there is potential for a second low to move in off the Atlantic later in the week, which could bring snow on its northern flank somewhere across the south, as it bumps into the cold air, but again a great deal of uncertainty, with models suggesting the idea one run only to drop it the next run.