Updated 21st July
Covering the period 28th July - 19th August
Warm, with southerly winds blowing more frequently than usual, quite sunny in central and eastern parts of the country. Dry early in the forecast period, but unsettled at times during early to mid-August, especially in the west.
With southerly winds blowing more frequently than usual, temperatures are expected to be significantly above the 1981-2010 average, with positive departures generally around 1.5C, although northern and western Scotland and Northern Ireland may be less than 1.0C above and some parts of southern England may be nearer 2.0C above.
Rainfall totals will be close to average in most counties, but with considerable local variations as there may be a significant emphasis on 'hit and miss' thundery downpours, rather than persistent frontal rain, especially in eastern and central parts of the British Isles.
Sunshine totals will be close to average in Ireland and western Scotland, but elsewhere they will generally be above normal.
Monday Monday 28th July - Sunday 3rd August
High pressure will be centred close to the west of the British Isles early in this period, but towards the beginning of August, pressure is likely to fall to the north and north-east of the British Isles, pulling some cooler air down from the north-west, and then lowest pressure will become centred to the north-west of the British Isles, swinging the winds around to more of a south-westerly direction.
Thus, between the 28th and 30th July, most of Ireland, Wales and the west and south of England will have dry, sunny and warm conditions, but northern and eastern Britain, especially the east of Scotland, will be more prone to banks of cloud rotating around the high pressure, and here temperatures will be close to the seasonal norm as a result. Between the 31st July and the 3rd August, the weather will become more unsettled in the northern half of the country with some weak fronts moving around the northern flank of a declining anticyclone, bringing some light rain at times, while the south of the country will remain mostly dry with generally above average temperatures and sunshine amounts, and it will become warm generally by the 3rd as we start to pull up warm air from the south.
Temperatures will be close to the seasonal average in the north and east of Scotland during this period but will generally be above average elsewhere, by up to 2C in south-western Britain, and maximum temperatures in central and southern parts of England will typically be between 22 and 25C. Rainfall totals will be close to average in northern Scotland, but elsewhere this period will be drier than average, and substantially so in western and southern counties. Sunshine totals will be close to average in Scotland and much of north-east England, but elsewhere it will be sunnier than average.
Monday 4th August - Sunday 10th August
Pressure will continue to fall in the eastern Atlantic, and so although there is greater uncertainty over how this period will pan out, it is likely to be changeable but rather warm across most of the UK, with southerly winds blowing more frequently than usual as a result of the low pressure to the west and relatively high pressure to the east. The jet stream, which has often been weak during this summer so far, is likely to remain on the weak side, so I do not expect a succession of low pressure systems moving west to east- the main emphasis will most likely be on shallow lows mainly centred to the north-west and west of Britain.
Thus, we are likely to see occasional belts of rain heading from west to east through the British Isles, these most prominent in the west of the country, but in between there will be significant brighter spells, especially for eastern parts of the country. The brighter spells are likely to produce scattered thundery downpours due to the proximity of the low pressure to the west, which means that there will most likely be significant local variations in the rainfall totals.
Due to the relatively high frequency of southerly winds expected during this period, temperatures are expected to be above the seasonal norm, typically by a couple of degrees Celsius. Rainfall totals will generally be above normal in the west of the country and close to normal in the east, although there will be significant variability from one location to another where totals are swollen by localised thundery downpours. Due to the expected lack of a strong jet stream, I expect sunshine totals to be slightly above average across the UK as a whole, with eastern parts of the country most likely to have above average sunshine and western parts more likely to have close to average sunshine.
Rest of the month
Monday 11th August - Tuesday August 5th
There remains a fairly strong signal for below-average pressure in the eastern Atlantic and slightly above-average pressure for central parts of Europe, so this period is likely to continue warm, but changeable at times, especially in the west, with an above average frequency of southerly winds. The frequency of cloudy, wet and breezy conditions is likely to increase in the west of the country as we start to see more vigorous depressions heading in from the Atlantic, but there will still be some drier brighter slots in between, and eastern parts of the country will have substantial drier brighter spells. The southerly winds may also bring some thundery outbreaks up from the continent at times.
Temperatures are likely to remain a couple of degrees above the seasonal average, taking the period as a whole. Rainfall totals are likely to be near average in the east and above average (though not exceptionally so) in many western parts of the country. Sunshine totals may drop a little below average in some western parts of the country, most likely in Ireland, but the east of the country will tend to maintain above average sunshine.