Jet stream shift to bring summer weather

1 07 2013

It’s usually true to say that confidence in a weather forecast decreases the further out you look.

However, we have a situation at the moment where we are actually more confident in the detail for this weekend and beyond rather than over the next few days.

This is because we are seeing some very strong signals for high pressure to dominate the weather from around Friday and then persist for several days afterwards.

In summer high pressure means fine weather, and it also looks like it will become very warm as well.

Normally we can’t give much detail beyond the 5-day forecast period, but with the current situation we can give a forecast beyond that with a higher than usual level of confidence.

So for, say, the Men’s Wimbledon Final on Sunday it looks like it will be dry and very warm with a good deal of sunshine. We are less confident in predicting who will be in the final, or who will be the winner, though.

As we go through into next week, it looks highly likely that one or two places will nudge towards the 30 C mark.

With this in mind, it’s likely that by the middle of next week we’ll have topped the current warmest temperature of the year, which was 27.2 C recorded at Heathrow yesterday (Sunday, 30 June).

So why will we be seeing high pressure develop over the UK to give us this spell of fine weather?

Well, to get this type of situation we need the jet stream to be in the ‘right’ place for this time of year – tracking to the north of the UK between Iceland and NW Scotland.

Chart showing expected position of the jet stream on 6 July 2013.

Chart showing expected position of the jet stream (shown in shades of green) on 6 July 2013.

In this position it guides rain-bearing Atlantic low pressure systems off to the north of the country, meaning the far north-west of the UK gets glancing blows from these systems while the rest of the country has more settled conditions.

We expect the jet stream to move into this position over the next few days.

Leading prediction models from forecasting centres around the world all seem to be in agreement about this development – hence the unusually high level of certainty in the forecast. But, of course, forecasts can still change – so do stay in touch with the latest in our 5-day outlook and out to 30-days ahead.


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