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This summer in the south of France we have had two hot months with 29 days over 30'C, while the average maximum is 26'C in July.

Normally there are violent storms with lightening up to 20 times a minute, and this year in two months we have had 20-30mm of precipitation rather than the average of 120mm, and there hasn't been any thunder and lightning since the 15th of june.

I am confused why we have only had meek drizzly rainfall, because of weak cold fronts, insufficient moisture from the east, did the high heat cause the rain to not condensate in the high atmosphere?

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This is an El Nino summer, and a very strong one and a very weird one at that. Weather patterns are messed up world-wide. Apparently a stable high pressure cell has set up that oscillates back and forth between just east of Barcelona to eastern Europe.

France suffers when that high pressure cell is just east of Barcelona. That high pressure cell off Barcelona means France is in that thick of it. Moderately high temperatures and low humidity rule the day. The chance of rain is drastically reduced, and the chance of abnormal high temperatures is drastically increased.

France suffers even more when that high pressure cell migrates to the northeast. Now the clockwise rotation of the high pressure cell carries extremely hot and extremely dry air from the Sahara towards France. If on the very odd chance that you do see clouds, and on the odder chance that you do see rain falling from a cloud, the odds are that you'll see the rain disappearing halfway to the ground.

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  • $\begingroup$ can you point at what pressure level is the high prressure cell from this site - earth.nullschool.net/#current/wind/isobaric/250hPa/… ? $\endgroup$ – gansub Aug 11 '15 at 5:37
  • $\begingroup$ I assumed you were writing about June and July, which were ridiculously hot in France. You are pointing to the current winds at the 250 hPa level. That's wrong, for a couple of reasons. Winds are great at finding low pressure regions, not so great for high pressure regions. Sea level pressure and the height of the 500 hPa level are better indicators. Another reason is that right now, it's about average in France. It's eastern Europe that's suffering now. $\endgroup$ – David Hammen Aug 11 '15 at 23:34
  • $\begingroup$ yep - iridl.ldeo.columbia.edu/maproom/Global/Atm_Circulation/… $\endgroup$ – gansub Aug 12 '15 at 3:06
  • $\begingroup$ Find this high pressure ridge in your winds: vortex.accuweather.com/adc2004/pub/includes/columns/newsstory/… $\endgroup$ – David Hammen Aug 12 '15 at 3:08
  • $\begingroup$ David - thanks. I also posted the monthly geopotential height anomaly at the 500 hPa level. $\endgroup$ – gansub Aug 12 '15 at 3:09
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The high temperatures may have been at least partly caused by subsidence in the troposphere, which inhibited convection and hence convective storms. Subsidence also contributes to high temperatures due to the heat of compression as air is forced to sink, enhancing heat due to insolation. Subsidence is common in the troposphere over deserts such as the Sahara that lie in the horse latitudes, where air from the tropical Hadley cell circulation subsides. It contributes to the lack of rainfall in these deserts, and to some extent also to the high temperatures. Of course, insolation in the tropical deserts is so strong that temperatures would still be high even without subsidence, but not as high as with it.

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