Posted by: mynaturaldiary | June 11, 2012

Siling doon

The vagaries of the jet stream are apparently beyond the reach of the Met Office 3 month forecast, which predicted at the end of March 2012 a drier than usual April. Instead we had:

When two strangers meet in Yorkshire, there’s a fair chance they’ll have a conversation about the ‘bloody weather‘. We currently suffer from being nithered (cold) and it’s siling doon (raining heavily) outside.

What’s going on?

The North Atlantic Oscillation, which is  currently negative

has helped push the jet stream well south of Britain.

When the jet-stream is blocked by high pressure it dips southwards and lets cooler air flood in from the Arctic regions.

The vagaries of the jet stream seem controlled by Rossby waves, which are difficult to predict over the long term (viz 3 months). The jet stream predictions over a medium time (~14 days) are getting better.

The following offers a guide to what the Jetstream does to British weather.

    • The position of the jet stream over the UK determines the type of weather we experience.
    • If the polar front jet is situated significantly to the south of the UK we will experience colder than average weather, driven by the polar cell.
    • If the polar front jet is situated to the north of the UK we will experience warmer than average weather, driven by the Ferrel cell.
    • If the polar front jet is situated over the UK we will experience wetter and windier than average weather.
    • If the polar front jet has a large amplification then cold air will travel further south than average and warm air will travel further north than average.
    • The direction and angle of the jet stream arriving at the UK will determine what source of air (i.e. cold, dry, warm, wet, from maritime or continental sources) the UK experiences.

jetstream

So the low/ high pressure systems around the Atlantic, and the jet stream begats the ‘bloody weather.

Of course, our summer migrant birds would prefer warm and dry summers, as would we. Let’s hope the jet stream heads north of Britain, and we warm up again, so we can begin complaining to each other about being mafted (too hot).

Responses

  1. […] We are in the grip of the polar cell until the jet stream moves North of us. […]


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