23 Oct 2013

Nasty autumn storm possible on Monday

There’s no doubt that the weather has turned very lively during the past week. Areas of low pressure have barrelled in off the Atlantic, bringing heavy rain and strong winds.

Sunday saw a suspected tornado hit Hayling Island in Hampshire, damaging around 100 homes and ripping up trees.

It’s common for the weather to be very unsettled at this time of year as the jet stream takes its seasonal journey southwards, in response to cooling taking place at higher latitudes.


The jet stream is driven by the temperature contrast between the cold poles and warm equator, with its path marked by the zone of greatest temperature contrast at mid-latitudes.

As the air becomes increasingly cold to the north of the UK, this increases the strength of this temperature contrast and causes the jet stream to pick up speed, as well as head south.

The end result is for low pressure systems to form over the Atlantic Ocean and then be catapulted towards us by winds of around 150mph at 30,000ft – the height at which planes fly.

Possible storm late Sunday into Monday

Something of particular concern that has been hinted at by the weather computer models in recent days is the possible formation of a nasty storm that could arrive later Sunday and into Monday.

It is worth emphasising that there is still a great deal of uncertainty with the exact track of the storm and how nasty it will be, but given that it is a possibility, it needs to be highlighted.

At the moment, different weather computer models are handling the severity and path of the storm differently.

The American GFS model takes the centre of the storm across northern England, which would give much of England and Wales gusts of wind of 50-65mph inland, with 65-80mph for coasts and hills.

However, the UK Met Office and European ECMWF model have a more southerly track for the storm, which would take the worst of the winds through the English Channel and over northern France.

Why such a range of possible outcomes?

The formation of storms is finely balanced and needs a number of factors to come together in the right place at the right time.

man_umbrella_g_wpIn order for a nasty storm to form, the fastest part of the jet stream at 30,000ft up needs to phase in time with the greatest zone of warmth, moisture and energy at the surface.

If they are slightly out of phase, the path and intensity of a developing storm can be affected hugely.

It is these subtleties that are making it difficult to pin down the detail at this point and is why the situation will need to be closely monitored in the coming days.

Even if we are spared a nasty storm, the weather through this weekend and into next week will still be wet and windy with gales.

Don’t forget, you can get the latest forecast on the Channel 4 Weather website. I’ll also be posting regular updates on Twitter – @liamdutton

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