UK meteorology

BTW, in the Netweather post, an elevated mixed layer refers to the leading edge of the cooler, drier air at height (upper levels of the troposphere) associated with the cold front. It is mixed, in that the cooler air is fairly homogenous in and of itself, but it lies above the hot, moist airmass currently over this area (I''m sweating as I type!) and is not yet mixed with that hot, humid airmass (hence it is described an an elevated layer).
Looking at my pine cone (alright - BBC weather) and with my finger in the air, it looks like the heatwave is reaching its end. A fresh breeze blowing in my Lincolnshire village tonight and a drop of 4 degrees C by tomorrow. No real sign of rain though and the temperature looks to be running around 2-3 degrees C above average for a good while yet. All good - hopefully a forthcoming trip to Rome won't come as too much of a shock, plus I've tomatoes to ripen and, if the trend continues into autumn, an October break in Norfolk should be pleasant :)
Short-range view from Malcolm on Netweather (part 1). It seems that northern areas are likely to experience a blast of cold at the weekend:

The outlook initially remains unchanged for this period with high pressure generally in charge but the position and orientation is such that that the north, particularly Scotland, is still susceptible to systems running around the northern flank of the high cell, But towards the end of the period this changes very quickly, courtesy of upstream developments, and much colder air plunges south over the UK down the eastern quadrant of the burgeoning subtropical high in the western/central Atlantic.

The 500mb and surface analysis for midnight and the 0300 WV image

After a pretty clear night over much of England and Wales. a little more cloud further north. it will be a dry and sunny day in many areas, albeit not overly warm, but rain will effect the north of Scotland as a front skirts the coastline and the wind will pick up during the day and will touch gale force over Scotland.

During the evening and overnight further rain over north west Scotland but the main feature is the strong wind, still touching gale force which has veered north westerly and moved south to also effect the north of England.

This is pretty much the story through Tuesday with rain across north west Scotland and continuing windy in the north with gales in exposed areas. Further south continuing dry and sunny and perhaps warming up a tad.

Part 2:
Wednesday sees the start of the transition with developments in the western Atlantic but the immediate effect closer to home is to realign our high cell which becomes more influential, thus winds abating in the north and resulting in a generally fine day with sunny intervals and relatively warm. Still some patchy rain across the west coast of Scotland

By Thursday the transition is well underway with the trough over the eastern seaboard initiating rapid amplification of the subtropical high in the western Atlantic which in turn facilitates the trough and cold air to plunge south to the north of Scotland. So that by midday the cold front is just about across the north coast of Scotland. Thus rain will spread down the west coast and to N. Ireland during the afternoon whilst the rest of the country again remains dry with sunny intervals.

Overnight and through Friday the cold front will track south reaching the south by the afternoon leaving in it's wake much colder air in a very strong northerly wind which could touch gale force in the north and north east. In this very unstable air frequent heavy showers will develop which will be wintry in the north with snow on the high ground and possible even at low levels. It goes without saying it will feel very cold.

And the NH profile at T120 sums it all up

Malcolm's view on Saturday 27th part 1:
Changeable weather over the next few days with temps remaining below average

The 500mb and surface analysis for midnight

Squally showers overnight, of snow over the high ground in Scotland but rain and rain/hail in the N. Ireland and and coastal regions of Wales and England. Note the Pembroke Dangler in the south west. These will tend to die out over N Ireland and Scotland during the day and become more concentrated along the east, south east coasts and central southern England as the wind veers somewhat. Elsewhere after a very frosty start very crisp and sunny but feeling very cold.

Showers continuing in the east overnight as the wind also continues to veer with the ridge edging across in the north. A widespread frost by morning

The ridge becomes more influential through Sunday but still very breezy in the south and once again showers of rain/hail. possibly some sleet, concentrated over eastern regions. Another very cold day but generally the wind has abated so less wind chill
Part 2:
By Monday the changes that have been mentioned in previous posts are underway with the amplification of the subtropical high in the western Atlantic forcing the next upper trough south east that also serves to reinforce the European ridge to the east of the UK At the same time activating the low pressure to the south where a wave has formed on our old front over south east France. All of which results in calm and bright, but still cold, day for most with a few showers lingering along the east coast.

By Tuesday both troughs are caught in the pincer movement of the amplifying ridges and thus any longitudinal movement ceases resulting in the aforementioned wave over France, deepening and tracking north into the southern North Sea. This will bring strong winds and possibly heavy rain to eastern regions but, obviously, the precise track of the low is the key to the extent of this.Whilst this going on elsewhere another dry and cold day after a frosty start

By Wednesday the North Sea low has filled and tracked north to be off the Norwegian coast and the Atlantic trough has taken closer order with a slack low pressure area to the south west and a waggly front up the Irish Sea. All resulting in patchy rain/showers in the west and dry with sunny intervals elsewhere and still cold

And the NH profile at T120