Increasing Risk of Dangerous, widespread and prolonged heat building over France, parts of Iberia, and spreading NE into Central Europe over the coming week which over France may last into the following week with temperatures approaching or exceeding 40C for a significant period of time.
A large ridge of high pressure is going to develop through the Tropopsphere , there will be both the strong advection of air from the south at 850mb but also there will be strong descent through the troposphere this under the ridge. The Ridge essentially maintained by two right exit regions of an Atlantic Jet and a NW Jet diving down into Russia
The Trajectory on the right, shows where the air will originate from at 500m on Friday at Bordeaux and takes it back to today. You can see it orignates in the Mid Atlantic, but the key is it is at well over 3000m nearly 4000m up - that is 13,000ft up. This shows the air is sinking (descent) and thus warming. The Sun is at its peak height in the Northern Hemisphere and Daylight is shortest. Its going to get very hot in this type of scenario.
The GFS Operational run shows 38-40C by Friday in the SW , W and Central France which has the potential to last well over the weekend and throughout the following week. The other chart is the following Thursday, that is a week of temperatures around or exceeding 40C . That is a long time of dangerous levels of heat. The GFS is a Global Model and will generally not pick up the local extreme temperatures.
This could be a very significant heatwave and should now be monitored closely over the next few days. This links to my other post which discusses the dry and anticyclonic theme likely the w/c 22nd June, with some runs of MOGREPS and GFS Suggesting temperatures into the 30s across Esp. Southern Parts of England by that time.
** This is a longer range discussion and doesn't represent a specific forecast ** but it important to flag it.