One of the problems with a heatwave is that inevitably in areas near the North Sea like eastern Scotland and north eastern England, coastal areas often have haar or sea fret when cold sea fog blocks out the sun and temperatures can be several degrees cooler than places inland.  It generally happens when warmer moist air moves over the relatively cooler North Sea causing the moisture in the air to condense, forming fog and visibility could be down to a few metres at times. The photo which was taken mid afternoon shows a bank of fog over the Forth which must be over 250 metres thick as the top of Arthur’s Seat (251 m or 823 feet high) in Edinburgh was almost obscured (above the gap in the woods at the very left of the photo)   Fortunately today it was not very extensive and did not cause the barley to be too damp to harvest although by the time I went to bed it was very thick outside.