BBC monthly outlook
Monday 14 August—Sunday 20 August
Sunshine and showers, turning cooler later.
After a couple of cool nights through the course of the last weekend, the working week will get off to a similarly clear and chilly start across the extreme east of the UK. Further west though, a low pressures system and its attendant weather fronts will bring outbreaks of often heavy rain, particularly for Northern Ireland, southwest Scotland and later Wales. Many central and eastern areas will stay dry with hazy spells of sunshine through most of Monday though.
Through Monday night into Tuesday, the same area of rain will gradually traverse east, giving a cloudy and wet start to Tuesday in the east, and a brighter start across western areas of the UK. The rain in the east should clear into he North Sea fairly readily though, leaving a theme of sunshine and heavy, thundery showers in place for the rest of the day.
Wednesday will most likely be a dry and bright day for all, following another relatively chilly start. Indeed, despite the sunny spells, temperatures will only just about peak at average across the UK, although conditions should still feel relatively fine in the sunnier intervals.
Overnight into Thursday will bring a further weather system in from the Atlantic, in association with an Atlantic low pressure system. The rain will clear to the east early on Thursday, leaving a legacy of sunshine, heavy thundery showers and a slightly cool feel will follow in its wake. Winds will tend to strengthen across northwestern areas of the UK too.
As we progress through the end of this week, it looks like the low pressure system that arrived close to northwestern regions on Thursday will edge away east, perhaps allowing a more settled start the weekend. At time of writing, most of the forecasting tools at our disposal are indicating that a further Atlantic low will move in to northwestern areas again to bring spells of showery weather, but there are signs that southern and eastern parts of the UK could stay drier and brighter for longer.
Monday 21 August—Sunday 27 August
Events in the western Atlantic affect our forecast
It should be noted that this forecast period is beset with an unusual level of uncertainty. At time of writing, the overwhelming majority of forecast solutions offered by a range of computer models suggest that a relatively deep area of low pressure will be positioned just to the northwest of the UK. Such an eventuality would mean that northwestern regions of the UK would again be under threat of further showers or longer spells of rain, relatively low temperatures for the time of year and strong west to southwesterly winds. Conversely, such a synoptic pattern would mean that southern England will most likely enjoy the best of the weather, with lengthy dry spells and temperatures edging up into the mid-twenties.
As we move through the period, most models suggest a continuation of the theme of low pressure to the north of the UK, with pressure remaining higher to the south, which will translate to weather conditions in the UK being roughly in line with the themes mentioned above.
The source of the uncertainty in forecast details throughout this period lies in the potential for significant tropical storm activity that is anticipated across the warm waters of the Caribbean and western Atlantic. This factor may at first seem rather inconsequential to the weather closer to our shores. It should be noted though that such tropical disturbances can inject a good deal of moisture and energy into the prevailing Atlantic synoptic pattern. The knock on effect is that small perturbations can form in the Atlantic jet stream, which are often missed by the forecasting models. These perturbations can have a large effect on the track of any Atlantic lows that pass close to or over the UK. As a consequence, there is a unusually low level of confidence for the forecast details for this period. Stay in touch with the BBC weather team to find out how the forecast develops over the coming days!
Monday 28 August—Sunday 10 September
Uncertainty continues into climatological autumn
The relatively high level of uncertainty in the forecast details described in the previous section unfortunately continue to be an issue throughout the remainder of August and into the first week of September, which is the start of the climatological autumn. At time of writing, the most likely scenario is that a strong Atlantic jet stream will continue to push weather systems in from the west to bring spells of rain, followed by intervals of sunshine and showers. Models continue to hint that high pressure will on occasion become established across the the southern half the UK, meaning that lengthier dry spells and slightly warmer than average conditions will most likely prevail across southern and eastern England, and perhaps southern areas of Wales at times.
Next week
With summer slowly coming to an end, and at this stage no real sign of any extended periods of hot weather, can we perhaps look into September and hope that early autumn will bring us a warmer spell? Stay across the latest developments in the longer term forecast here at BBC Weather!
http://www.bbc.co.uk/weather/2635167#outlook