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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?

bandybabboon
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2 Answers2

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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.

David Hammen
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  • can you point at what pressure level is the high prressure cell from this site - http://earth.nullschool.net/#current/wind/isobaric/250hPa/orthographic=3.91,37.95,289 ? –  Aug 11 '15 at 05:37
  • 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. – David Hammen Aug 11 '15 at 23:34
  • yep - http://iridl.ldeo.columbia.edu/maproom/Global/Atm_Circulation/Monthly_Height_500hPa.html?T=Jul%202015 –  Aug 12 '15 at 03:06
  • Find this high pressure ridge in your winds: http://vortex.accuweather.com/adc2004/pub/includes/columns/newsstory/2015/650x366_08111530_hd21-1.jpg – David Hammen Aug 12 '15 at 03:08
  • David - thanks. I also posted the monthly geopotential height anomaly at the 500 hPa level. –  Aug 12 '15 at 03:09
  • Besides, you asked about two months, not now. Paris was right at its historical high on August 11, will be hot (but not unseasonably hot) on August 12 & 13, and then cool for a few days. What you see now does not explain what happened a month ago. – David Hammen Aug 12 '15 at 03:11
  • I am not the original OP of this question :-). I was just curious about the ridging and thanks for the clarification. –  Aug 12 '15 at 03:15
  • Thanks, it's a very informative answer indeed. I still don't know what has happened to the lightning and hot humid thunderstorms. Today there was wind up to 100kph and i saw some heavy concrete tiles flapping on the roof. It rained 2-3mm, there was zero thunder and lightning. Yesterday, 36'C, today 100kph winds and some rain, no lighntning storm, perhaps there was some thunder elsewhere. added an image of todays rainradar to the question. I am puzzled. – bandybabboon Aug 13 '15 at 20:24
  • if you see the 12th and 13th of august at the weather station, you can see: yesterday 37.4'C, today gusts of 74kph, temperatue dipped to 17-19 'C at the same time as it was 37.4'C yesterday, a cold front with only 3mm of rain and no electric activity. http://www.infoclimat.fr/observations-meteo/temps-reel/saint-etienne-boutheon/07475.html – bandybabboon Aug 13 '15 at 20:32
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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.

Jack Denur
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