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Bank Holiday weekend confusion

Posted Tue, 23rd May 2017 19:05

The weather prospects for the Bank Holiday weekend are still uncertain. Computer models are having difficulty pinning down the extent of the rain risk.

Saturday warm or wet?

The next few days will bring a lot of dry and very warm weather. Unfortunately the picture becomes more complicated as we head into the Bank Holiday weekend. Low pressure in the Atlantic will be influencing our weather more and its associated weather fronts could bring some heavy and thundery rain. This afternoon's GFS12z model run shows wet weather affecting large parts of the country on Saturday afternoon, and with a lot of cloud cover temperatures are capped even in areas where it remains dry.

 GFS12z rainfall

 

The GFS12z run is out of step with a number of computer models including the GFSP. The GFSP is the in-development GFS upgrade which is scheduled to go into production in late June. At the same time it shows the rain farther southwest and much of the UK has a fine and very warm or hot day.

 

GFSP rainfall forecast

 

Which outcome is more likely?

It's a Bank Holiday weekend so Sod's law says the GFS is bang on the money. I'm going to differ and be optimistic. The GEFS postage stamp data (basically the GFS model initialised 20 times with different starting conditions) suggests a dry and very warm day is probable away from the south west. The plot below shows forecast rainfall for 12:00 on Saturday 27th May. The vast majority of the runs support the GFSP scenario. 

GEFS06z rainfall postage stamps

 

Beyond Saturday the GEFS (the 6z update ) is quite mixed. There is the potential for some heavy and thundery showers during Sunday and Bank Holiday Monday. Very warm and sunny periods are likely too and some parts of the UK may remain mostly dry. On balance I'd say things look quite promising but it could still go either way. By this time on Thursday things should have firmed up. 

TL;DR

The Bank Holiday weekend weather outlook isn't nailed down. Saturday will probably be fine and very warm in much of the country, but there is low risk of heavy rain extending eastwards. On Sunday and Bank Holiday Monday warm sunny periods may continue but thundery downpours could become more widespread.  

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