Big gap between what Arpege (and the Met office for that matter) is saying for Thursday and the GFS output / various automated sites which show it cooling down relative to today. 

Arpege was closer to the mark today than most of the output.

Just like the thing though, we (here in Edinburgh and on the east coast) are plagued by easterly winds once again, along with cooler temperatures resulting from that and yet more easterly muck coming in from the North Sea whilst all of that is going on.

https://www.metoffice.gov.uk/public/weather/forecast/u10fvgptv#?date=2018-06-26

A forecast high of 17c here today....hmmm.  I predict around 22c here close to the coast and 25 c at the other end of town. (3 miles way)  Raw Met O maxes forecast compared to actual could therefore be as much as 8c out today in Dover

Edit - late afternoon -  maxed here at 22c earlier in the day.

The raw Met Office maxima really are off the mark for many areas. Today’s forecast here suggests a max of 13°C (11am to 4pm) and up to 15°C tomorrow. 

Its beyond a joke and frankly worse than useless and misleading. Its already 15.1 c here. So at 7 am we are close to the daily forecast max.  

A northern pessimist! 30.1 in London even as you post, and the way things are looking this morning, I'd be very surprised if 30C wasn't reached in several places this week up to Thursday. Severn Valley is the favoured spot for my money as a easterly drift sets in. Even your area might benefit from being the right side of the Pennines

Given how crap the temperatures were yesterday once the easterly set in they don't seem wildly unrealistic to me.

Today we have the horrid winds from the off so not a warm morning like yesterday. 13.4C now and could easily drop if the wind increases in strength.

No heatwave here as more easterly muck coming in from the North Sea during the night has resulted in the re-commencement of the annual June permacast in this part of the world, and temperatures of just 12ºC in Edinburgh.

Temps flying up today widely 24c already wouldn't be surprised if somewhere hits 90f. 

Trawsgoad 26.2c already

Rocketed into the mid-20s here by 10 am this morning after a low of 11.1 (almost 2*C up on yesterday's), but now there seems to be a bit of a sea breeze already - the pressure pattern is too slack and irregular to keep it at bay as long as was the case yesterday.

It's only a weak breeze though. Nearshore water obs are showing anomalies of +3 to +5*C which translates to actual temps of around 16-18*C extending out about 10 miles into the Channel. I expect this warming and resultant weakening of the sea breeze will continue until at least late afternoon on Saturday - it will be interesting to see just how high the sea surface temperatures climb.

Still thinking 28*C is achievable here today, as the high re-orientates slightly and provides a little more opposition to the sea breeze by the afternoon.

Regardless, it's very, very dry out there. This coming Sunday and/or Monday continues to look like the start of a 2-3 day risk/reward situation (lightning risk, rain reward). 

Trawsgoed definitely going for 90f 28.9c at 12.

Meanwhile in Greece, the weather is nothing like June

http://www.northmeteo.gr/agios-nikolaos/index.php?lang=en

30C in Manchester and Liverpool. 

Still, it finishes in fourth place in my list of warmest days on record, as well as setting a new record for June.

1. 34.0°C on 1 July 2015

2. 32.0°C on 19 July 2016

3. 31.0°C on 1 August 2013

4. 30.4°C on 26 June 2018

Officially the hottest day of the year again 30.6c Porthmadog 

The Tepidwave continues here with a max of 17.9C at 11:30am. Now it's evening it's the usual cold, overcast crud. 13.8C at the moment. 

Even the vast majority of summers over the past decade have managed better than this.

Shocking stuff. I'm off to Puglia for a fortnight in July and noticed the weather has been very poor there recently. Downright vile in fact with several days of rain and cloud and temperatures struggling to 20C today.

Thankfully things look like settling down to normal conditions soon as that is the last thing you would expect that far south in summer. I was concerned temperatures might be too hot so hopefully it won't go from one extreme to the other.