Parts of the US and Canada are seeing particularly cold weather and heavy snowfall at the moment.
Chart showing the position of the jet stream over North America as at 00:01 on 20 November.
A southward buckle in the jet stream has seen cold polar air flow south to north eastern parts of North America.
In the Buffalo region of New York state, temperatures have fallen as low as -15C and 4-5 ft (about 1.5 metres) of snow has fallen – enhanced by what’s known as the ‘lake effect’. Another 2-4 ft (about 1 metre) is expected through today.
The snowfall is set to ease on Friday with much milder conditions through the weekend giving a rapid and significant thaw – which could bring a risk of flooding.
This risk could increase through the start of next week when some very heavy rain is expected across the area.
What is lake effect snow?
Lake Superior (top left) and Michigan (centre) can be seen generating ‘lake effect’ snow. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE
This is an effect which applies to areas around large lakes like those seen in the northern US – Lake Superior has an area of more than 30,000 sq miles.
When cold air moves across the relatively warm waters of the lake, air rises due to convection which creates clouds and heavy showers. In cold conditions, the moisture in the clouds will fall as heavy snow.
As Buffalo as it the eastern tip of Lake Erie it has been particularly susceptible to this effect during the recent weather.
While we don’t have any lakes big enough for this effect in the UK, we can occasionally see a similar scenario when we get easterly winds in the winter.
Cold air from the continent can be warmed by the relatively warm North Sea as it moves across the water, bringing snow showers to eastern parts of the UK. However, there’s no sign of this in the immediate future for the UK.
Will the US weather affect the UK?
Many people believe that there’s a rule of thumb that weather in the US will arrive in the UK a few days later – but that’s by no means always the case.
In this instance, there’s high confidence that the cold snowy weather will stay on the western side of the Atlantic.
Also, in past winters similar weather situations in the US have strengthened the jet stream and increased the risk of storms across our shores. Again, in this instance, this isn’t expected at the moment.
What we do expect to see is further changeable weather over the coming few days.