BBC monthly outlook
Monday 12 June—Sunday 18 June
A northwest/southeast split, and warming up.
After a windy and showery start across Scotland, much of the UK will enjoy a mostly dry day, although skies will tend to be rather cloudy at times. The odd shower will likely affect northern and western areas at times, with the best of the sunshine reserved for southern and eastern England.
In fact, the pattern of Monday's weather will often be repeated throughout the bulk of this period, with breezy, showery weather crossing Northern Ireland, northwest England and western Scotland on all days. Much of the remaining parts of England and Wales, and also sometimes eastern Scotland, will often be fine and dry. The exception to this rule is that there will be a slight threat of the odd thundery shower crossing the far southeast of England on Thursday.
This general set up is the result of the anticipated jet stream position being just to the northwest of the UK, steering any Atlantic lows and their attendant weather fronts across northwestern regions, and allowing pressure to build from the south.
As we head into the weekend, the weather forecasting models and tools at our disposal suggest that pressure will continue to build from the south, meaning that the majority of the UK should experience some fine and relatively warm weather, with only the extreme north under threat of wetter and windier conditions.
Monday 19 June—Sunday 25 June
Warm and dry for most at first, but for how long?
This period will most likely start on an anticyclonic note, with the majority of the UK enjoying fine an dry conditions. The feel of the weather will however be greatly influence by the exact position of the anticyclone. Should the system be centred slightly to the west, a broadly north to northwesterly flow will maintain average temperatures, which will still feel quite pleasant. However, should the anticyclone be centred over or just to the east of the UK, some very warm air could be drawn up from the near continent. At the time of issue, there is very little computer model consensus on the exact positioning of the anticyclone. So although we are fairly confident in dry conditions for most, just how warm conditions get is still open to some doubt.
As the week progresses, there are increasing signs in the forecast models that the high will tend to break down, and further Atlantic weather systems will begin to impinge on the UK, bringing spells of wet and windy weather again. These unsettled spells will once again most likely be chiefly steered across north western regions of the UK, and it's also probable that temperatures will return to values nearer the average for the time of year.
Monday 26 June—Sunday 9 July
An uncertain picture for late June and early July.
There is always an inherently lower degree of confidence in the forecast detail for the longer range period, but even taking this factor into account, the uncertainty in forecast for the start of July is particularly high. At time of writing, there is very little computer forecasting model consensus for the type of weather pattern we can expect during this period, particularly as we head into early July. During the winter months, in addition to computer models, meteorologists can often use observations in weather patterns and phenomena on the other side of the globe to help shape ideas for longer range forecasts closer to home, but these methods do not correlate as well during the summer.
At the start of this period, conditions will most likely be wet and windy at times, particularly in the north and west, with drier weather often found across eastern areas of the UK. Beyond the end of June, the only consistent signal from the tools available to us is that of slightly higher pressure in the vicinity of the UK during the first week of July. Some models also hint that this pressure anomaly might be positioned slightly to the west. These factors lead us to forecast that for the beginning of July, the most likely prevailing conditions across the UK will be drier than average weather, with a slight downwards trend in temperatures, although with daytime maxima probably still above values normally expected in early July.
Next week
Find out next week if we can firm up on the forecast trends for the first half of July.
http://www.bbc.co.uk/weather/2635167#outlook