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Glastonbury Forecast 15 - 21st June



Time for the latest update,

Please get involved on the dedicated Glastonbury forecast thread on the main forum here


Thanks for all your nice comments on Twitter, I know that many of you will be going off to Glastonbury, and given the theme of this blog. The forecasts will continue right up to the start of the festival, and there will be updates as well during the festival itself. please get involved on conditions on site both of the weather itself and of ground conditions. The updates of ground conditions helped me tweak the forecast.

One final thing, this blog has been quoted now in the Guardian and the Huffington Post, I just hope my forecast is close to the mark.

Moving onwards to the actual forecast.

[b]General Theme[/b]

As we all know by now there will be unsettled weather across the UK on Saturday as a Low Pressure system moves eastwards across the UK and this will provide some moderate rainfall for Glastonbury. On Sunday the low pressure system is set to weaken and move steadily North Eastwards, south western parts of the UK are likely to have some of the best weather, but some showers are still possible, these becoming increasing isolated and lighter as the day progresses.
High Pressure is slowly set to push in from the South West next week, giving mostly dry and settled conditions, how dominant this becomes and whether it will last until the end of the festival, will be discussed as per each model run later. Sorry for the copy and paste from yesterdays forecast.

[b]GFS Operational Runs[/b]

Both runs show pressure slowly ridging up from the South West on Monday (1024mb), both runs have this ridge a little bit flatter than the on forecast yesterday. The ridge continues to edge further north by Wednesday (1030mb), with the 12Hz run pushing it a bit further north, both runs keep low pressure centred to the west of Iceland. Thursday sees low pressure starting to squeeze down from the North, but with pressure weakening but still remaining over 1024mb for southern areas. This squeezing process continues over the weekend as fronts push in from the west on Saturday, with the 12Hz allowing any fronts to edge that little bit further south. Sunday sees the first big difference between the models, the 06Hz run sees a ridge of High Pressure re establishing itself, while the 12Hz sees low pressure edging in from the North west.

In terms of rainfall from Monday onwards both runs are pretty dry from the Monday through to the Wednesday with only the odd shower. For Thursday and Friday, there is the slight risk of fronts trying to edge in on the westerly wind, the 06Hz run dissipates this before reaching the south on Friday morning, while the 12Hz has maybe something enough to wet the ground again for Friday morning. The models try to repeat this into Saturday, the 06Hz run keeps southern areas dry, while the 12Hz run has a little bit of rain reaching southern parts. Sunday looks dry on the 06Hz run, while the 12Hz run has a little bit of rain for Sunday night.

In Summary the 06Hz run looks very promising with very little rainfall, the 12Hz shows a little bit of rain for the weekend, nothing much to be concerned about at this stage, but we don't want the whole pattern edging south, as this coming weekend was initially forecast to have Low pressure further north.

Charts shown in order 06Hz (Mon 24 June, Wed 26 June, Fri 28 June and Sun 30 June)
[attachment=175428:GFS 21 06 1.JPG] [attachment=175427:GFS 21 06 2.JPG] [attachment=175426:GFS 21 06 3.JPG] [attachment=175425:GFS 21 06 4.JPG]
Charts shown in order 12Hz (Mon 24 June, Wed 26 June, Fri 28 June and Sun 30 June)
[attachment=175424:GFS 21 12 1.JPG] [attachment=175423:GFS 21 12 2.JPG] [attachment=175422:GFS 21 12 3.JPG] [attachment=175421:GFS 21 12 4.JPG]

Rainfall Next 6 days
Both runs have around 8-10mm of rain forecast, nothing substantial really.

[attachment=175430:Rmgfs144sum 21 1.gif] [attachment=175429:Rmgfs144sum 21 2.gif]

[b]GFS Ensembles[/b]
Both ensembles continue with theme of pressure rising steadily next week to around 1030mb, with a slow decline in pressure around Thursday onwards to around 1020mb.

The 06Hz maintain the theme of a very dry festival, however the 12Hz does have a few spikes indicating an increased chance of precipitation over the weekend.

06Hz run
[attachment=175438:GEFS 21a 1.png] [attachment=175437:GEFS 21a 2.png] [attachment=175436:GEFS 21a 3.png] [attachment=175435:GEFS 21a 4.png]

12Hz run
[attachment=175434:GEFS 21b 1.png] [attachment=175433:GEFS 21b 2.png] [attachment=175431:GEFS 21b 4.png] [attachment=175432:GEFS 21b 3.png]

This indicated a mostly dry and settled start the festival week probably right through to Friday, with an increased risk of some rain over the weekend.


Both runs show pressure slowly ridging up from the South West on Monday (1025mb), both runs a little bit quicker in doing so than yesterday's charts. Both charts have the ridge extending North Eastwards by Wednesday, but neither quite as far north as yesterday's runs, but the 12Hz a bit further north compared to the 00Hz and compared to the GFS runs. The 12HZ ECM run is also very similar to today's UKMO 12z run (not shown) Friday sees High Pressure over southern areas in both runs with Low Pressure to the North, the 12Hz has the High Pressure a bit further north. For the weekend both runs keeps any low pressure further away to the North and East with a ridge over South Western areas, this minimises the risk of any weekend rainfall.
Charts shown in order 00Hz (Mon 24 June, Wed 26 June, Fri 28 June and Sun 30 June)
[attachment=175442:ECM 21a 72.gif] [attachment=175441:ECM 21a 120.gif] [attachment=175440:ECM 21a 168.gif] [attachment=175439:ECM 21a 216.gif]

Charts shown in order 12Hz (Mon 24 June, Wed 26 June, Fri 28 June and Sun 30 June)
[attachment=175446:ECM 21b 72.gif] [attachment=175445:ECM 21b 120.gif] [attachment=175444:ECM 21b 168.gif] [attachment=175443:ECM 21b 216.gif]

[b]Upper Charts[/b]
[attachment=175451:610day.03 21.gif] [attachment=175450:814day.03 21.gif]

Again this favours a ridge of High Pressure for western areas, perhaps slipping away, but always tending to remain for the south west, to me this goes against the risk of low pressure massively effecting next weekend.
[b]Summary [/b]
While some rain is expected tomorrow and to a lesser extent Sunday, the start of next week through to around Friday is looking dry and mostly settled weather with some sunshine likely for good measure. There is a risk of some rainfall towards next weekend, but this is likely to be very light. For the weekend itself, some conflicting models, some are going for completely dry, others are gonig for some rainfall, while this is not expected to be massively heavy, there is an increased risk of some rain next weekend. This is something to keep an eye on, hopefully we will have a better idea of this likelihood by the start of next week.

[b]Ratings :- [/b]
Yesterday in brackets
Festival Dryness (0= washout, 10=dry) 7/10 (7/10) Still looking dry for the start of the festival, an increased risk of some rain over the weekend according to some models.
Ground Mudbath Rating (0=mudbath, 10 = dustbowl) 6.5/10 (6/10) With the site remaining in good condition and low to moderate at worst rainfall expected between now and at least next Friday, the risk of a mud bath is reduced significantly from recent days.
Heatwave rating (0 = freezing, 10 = heatwave), 6/10 (5.5/10) Currently temps mid teens/low 20s, perhaps a bit cooler over the weekend

[b]Newspaper Taglines [/b]
Bring your suncream and Sunglasses as it looks a dry, and possibly warm and bright start to the festival, There remains a risk of rain over the weekend, so still hire those wellies and a brolly just in case.


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