The UK Met Office has issued an all-day snow warning over East Anglia, Lincolnshire, the Home Counties and even London for Saturday 16th Jan. Further north there is a Snow and Ice warning from midnight and through Saturday day over Scotland, northern England down into the Midlands. The North York Moors look to be the sweet spot for new fresh deep snow but Lincolnshire and Norfolk could also see a decent covering.
But what about this SE warning area, have you got eager children clutching wellies and sledges wanting out after a week of penned in home schooling. Or are you worried about the impacts of this potentially wintry weather for essential travel?
Looking at the various layers through the atmosphere you wouldn’t hold much hope of snow looking at the thickness charts. The higher 500-1000hPa layer and lower 850-1000hPa show how the cold air over eastern Britain today and linked to Thursday’s snowfall, fades. These thickness layers record in metres or tens of metres the distance between two pressure levels. Cold air is more dense so takes up less space. 528dm is often highlighted a key thickness for snow over the UK, you can see that out east on Fridays’ chart.
The colder air over eastern Britain is being squeezed out during early Saturday and that is the trend of the day that milder air will reach over western and southern parts with any snow turning to rain in the south. However, the surface charts give more hope. If all the layers were cold up through the atmosphere then forecasters would be feeling more confident about this weekend forecast. However, this is relying on an undercut of cold air in a southerly flow off the continent. It takes until mid-afternoon to shift from eastern East Anglia and Kent. You can see on the chart below the blue area where precipitation will freeze, so snow is more likely over SE and eastern England tomorrow morning. Also the leap up of the freezing level within the warm sector, the orange area. That's the spoilsport rain area.
The incoming frontal system has a warm front, following cold front and occlusion. As the frontal band of rain continues to occlude out during the early hours of Saturday, that warm sector air is lifted away from the surface with the cold air ahead. The triple point (where various fronts meet) is where there will be heavy precipitation.
There is now an increased signal for snow to low levels over eastern England during Saturday morning. The areas highlighted by the Amber warning as having a higher likelihood of impacts from the snow are East Anglia into Hertfordshire.
East Riding of Yorkshire and the North Yorkshire Moors look to see significant snowfall whilst it is still dark and then Lincolnshire around daybreak.
There should be snow over the higher ground of Surrey and Kent but that will soon turn to rain and be gone. London? Well, it looks at most to be fleeting, slushy. Might get a covering for an Instagram photo. Although forecasting snow is notoriously tricky over the UK and this set up has a lot of bits finely balanced.
There is a lot of water about from recent rain, longer-term soggy ground and with this episode and any snow melting it means that the risk of flooding continues. Conditions on the roads for essential travellers will be poor. Ice, slush and snow. Poor visibility, surface water and spray.