Wednesday the 21st starts with high Pressure centred over Northern or North Eastern parts of the UK, so probably a settled day. However the exact location of the High Pressure is important going forward as some models suggest the High Pressure to the North East of the UK with the risk of low pressure trying to edge in from the South West over subsequent days.
At the moment, the majority view is staying mostly settled over the UK until the Friday, with only the GFS 06Hz turning it unsettled sooner with heavy rain on the Thursday.
Left to Right - ECM 12Hz run, GFS 18Hz (best case), GFS 06Hz (worst case) you can already see, the high Pressure starting to look ominous from the West.
After the music starts
For Friday through the weekend GFS and ECM have different ideas.
ECM – Both runs have it turning Unsettled early Saturday, with Low pressure to the North and north West of the UK, so turning a little cooler and showery conditions most likely.
But neither run looks that wet.
GFS – The 12hz run has high Pressure slowly moving away on the Saturday, with westerly winds edging in by the Sunday, Total rainfall 1-5mm, Temps low 20s, perhaps mid 20s Friday and Saturday.
The 18hz run has High Pressure slowly moving away early Sunday, so staying mostly dry with rainfall 1-3mm, with South Easterly. Temps generally low 20s.
The 06Hz has SW winds by the Thursday with Low pressure to the West of the UK, and fronts edging Eastwards on the Thursday and at times over the weekend, Total rainfall 15-20mm.
The 00Hz run keeps High Pressure to the NE, but with low pressure edging in from the West /South West on the Friday, with a front slowly edging Eastwards on the Saturday. Total rainfall 5-10mm.
Left to Right - ECM 12Hz run, GFS 18Hz (best case - no real dominant weather pattern), GFS 06Hz (worst case - rather unsettled from the west)
Left to Right - GFS 18Hz (best case - minimal rainfall for Glastonbury), GFS 06Hz (worst case - 15-20mm of rain)
The 6-10 day chart, which exactly covers the festival period, suggest High Pressure to the East of the UK, with Lower Pressure further west.
Pressure peaking around over 1028mb by Sunday with good ensembles agreement. Thereafter, pressure dropping back to just below 1020mb by Wednesday, thereafter a split between those keeping pressure above 1020mb and those dropping to around 1010mb, the 06Hz op goes for the more unsettled cluster.
The rainfall amount form the ensembles are quite small, and the 06Hz run is an outlier in terms of the heavy rain on the Thursday.
Currently looking dry and mostly settled until the start of the festival. As a result ground conditions are expected to be dry when the gates open, with the ECM now also suggesting a dry settled run up.
Over the weekend things are not so clear cut, with some unsettled conditions possible at times over the weekend bringing some rain or showers at times, but as ever some uncertainty.
Even more uncertainty as to the temps, with some GFS runs having temps in the low perhaps even mid 20s.