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Summer 2016 update 3

Matt Hugo's view


20/04/2016

What does summer 2016 have in store? The TWO summer forecast will be issued in late May but throughout April independent meteorologist Matthew Hugo, BSc, FRMetS, RMet will be giving us his view on what the current data is suggesting.

IMPORTANT: This may or may not correspond with the TWO view.


Overview

1) Latest seasonal models have changed in the idea of a progression towards more unsettled conditions through the summer and this, as a result, creates a greater amount of uncertainty over the latest predictions.

2) The cold SSTs (Sea Surface Temperatures) within the North Atlantic have continued however and this region of below average SST’s is still thought to have some influence on summer weather patterns with more unsettled conditions developing as the summer progresses.

3) The latest thoughts are for quite an active hurricane season, especially compared with the last few years and this may also reinforce the risk of more unsettled conditions later in the summer period.

4) The latest EC Seasonal, UKMO GloSea and CFSv2 seasonal models have lowered the risk of low pressure becoming dominant through the summer period which provides a distinct lack of consistency within the seasonal models for the summer period now.

By by simonwakefield [CC BY 2.0], via Wikimedia Commons

Latest seasonal model analysis

The mid-April period now provides a more comprehensive set of updated seasonal charts and information with the likes of the EC Seasonal, UKMO GloSea and CFSv2 models all being updated within the last week or so. It is with interest to highlight that the April update of the EC Seasonal model now has a slight bias towards higher pressure over and just to the west of the UK for the period that is June, July and August and this highlights a potentially drier than average summer as a result.

Temperature predictions from the EC Seasonal are more open to speculation with little bias towards above or below with generally near average temperatures preferred, which from a UK’s point of view would still support some warm or very warm weather at times. This change in evolution for the summer period creates a distinct lack of model consistency after the March updates produced a likely evolution towards more unsettled conditions through the summer period.

The UKMO GloSea seasonal model (updated 11Apr16) has lost its signal for lower than average pressure to become influential as the summer progresses and now provides a rather vague output for the summer period. On balance there remains a signal for below average temperatures to be present through the summer period to the west of the UK, as exampled on the image on the right below. But overall there is now more in the way of a bias towards near or perhaps above normal temperatures for the summer period, particularly across central and eastern areas of the UK.

UKMO GloSea 1

The signal regarding pressure through the summer is particularly vague in the latest update with a slight bias towards near-normal sea level pressure which would generally equate to reasonable summer conditions with the likelihood of the Azores high pressure building into the UK and bringing summer conditions at times.

UKMO GloSea

The latest CFSv2 seasonal model has most certainly shifted towards a signal for higher pressure to be more influential than compared with the last update. The latest (15Apr16) update clearly indicates higher than average pressure over the UK for most of the summer period, but especially June and July with perhaps a weakening trend into August. This tentatively supports the on-going predictions of a progression towards more unsettled weather through the summer, but compared with previous updates this latest update supports a far better summer across the UK given the signal for more in the way of high pressure than low pressure overall.

CFSv2 500mB height anomaly

Summary

The change in the seasonal model output has certainly created uncertainties and inconsistencies within the seasonal forecast for this summer across the UK. Seasonal models, even like short-range forecast models, can and often do change with the various updates, but as with short-range forecasting consistency is still looked for, but at the moment that just isn’t evident. There remains an underlying connection between the below average SSTs across the North Atlantic and an overall poor UK summer, along with a connection that a change from El Nino conditions to La Nina may also lead to more unsettled conditions. This is highlighted by the quote from a UKMO blog from last year:

"Closer to home the North Atlantic is more than 2 degrees colder than normal. It seems quite likely that the unusually cold North Atlantic has strengthened and pushed our jet stream south, also contributing to the low pressure systems that have dominated our weather" (ref: UK Met Office)

At this juncture the prediction from previous weeks is tentatively followed and that is to suggest that the start of the summer period, especially June and perhaps into July may well provide the best of the summer weather, whilst more unsettled conditions then develop through August and late summer in general. However, the latest seasonal models do contradict this evolution and prediction now and further updates of the seasonal models will provide fascinating analysis in the coming weeks as to whether this signal for higher pressure through the summer is maintained from the likes of the EC Seasonal and the CFSv2 or whether a change back to more unsettled conditions is signaled.

Matt will be providing weekly updates on the summer weather prospects throughout April.

Issued by: Matthew Hugo, BSc, FRMetS, RMet

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