North east US braced for snowstorm

Just over a week after much of the US felt the effects of its coldest weather in decades, more cold air is plunging into north eastern parts of the country.

During the next 24 hours, a large swathe of the north east US from the Midwest to the east coast will experience a snowstorm that will deliver six to 12 inches of snow (15-30cm).

The worst affected areas will also include the nation’s capital, Washington DC, as well as New York City and Boston, that encompass tens of millions of people.

There’s no doubt that it will cause severe disruption to transport, with major travel delays expected at many airports.

An additional problem with the snowstorm is that the wind will be brisk, resulting in very poor visibility and causing lying snow to blow around.

Why so cold?

As with the weather here in the UK, the weather in the US is largely governed by the jet stream – the fast-moving ribbon of air five miles up in the sky.

Its position and speed is crucial in determining the weather that is experienced by us at the surface.

So far this winter, the position of the jet stream over North America has been seemingly locked into a persistent pattern of heading northwards off the west coast of the US, before reaching up into central Canada, then diving southwards across the north east of the US.

As it reaches into central Canada, it is scooping up some very cold Arctic air and dragging it southwards into the north east US – hence the frequent spells of cold weather.

Recipe for a snowstorm

In order for a snowstorm to form, there are a number of key ingredients, one of which I have already mentioned – cold air.

The second is an area of low pressure, which the jet stream also plays a huge part in forming. When the jet stream dips southwards and forms a U-bend shape, it creates something known in meteorology as an upper trough.

This upper trough effectively causes air to rise more readily in the atmosphere, leading to clouds forming and subsequently precipitation falling – in this case, snow.

The final ingredient is a good supply of moisture in order to feed the storm and allow clouds to grow. This comes from the fact that the wind around the storm is coming off the Atlantic ocean, dragging in air that has a rich supply of moisture.

How long will the cold persist?

Looking at the latest forecast, there are signs that the cold weather across north eastern parts of the US may persist for around a week.

Temperatures in New York City are expected to stay below freezing during the day and fall to around -10C during the night.

Such low temperatures mean that any lying snow is likely to hang around for some time, which will cause additional problems with ice.

I’ll be keeping an eye on the snowstorm as it develops and posting updates on Twitter – @liamdutton