Another Record Rainfall in Southern France

Because of global warming, the atmosphere has contains more moisture than it used to. When it comes into contact with colder air, it can result in heavier precipitation.

http://www.wunderground.com/blog/weatherhistorian/comment.html?entrynum=308

By: Christopher C. Burt , 8:12 PM GMT on September 30, 2014

It is hard to believe that another rainstorm of equal intensity to that which I blogged about just 11 days ago has again struck the Languedoc Region of Southern France. This time the focus of the storm was centered over the city of Montpellier, Herault District, near the Mediterranean Coast.

Montpellier, a city of some 240,000, was deluged with an all-time 24-hour record 299 mm (11.77”) of rainfall between 8 a.m September 29th and 8 a.m. (local time) September 30th. This is the equivalent of almost four times the average monthly precipitation for September in the city. Its previous 24-hour rainfall record was 187 mm (7.36”) on September 22, 2003. Some private weather stations in Montpellier reported totals of up to 325 mm (12.80”) according to a German weather forum monitored by Michael Theusner of Klimahaus in Bremerhaven, Germany.

Of the official 299 mm total in Montpellier, an amazing 184 mm (7.24”) of this fell in just two hours between 3 p.m. and 5 p.m. on Monday (September 29th) and 252 mm (9.92”) in three hours from 3 p.m. to 6 p.m.

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The two-hour total would be a new French national record for rainfall intensity, surpassing the 180 mm (7.09”) measured at Saint-Gervais-sur-Mare just 13 days ago on September 16th! Prior to this month’s extreme rainfalls, the previous greatest two-hour rainfall total observed in France was 178.4 mm (7.02”) at Solenzara on October 26, 1979. However, it should be noted that records in France for short-duration rainfalls only go back to the 1960s or 1970s and do not include every meteorological site in the country. Nevertheless, it is pretty shocking that two such amazing rain events have occurred in the same region over just a two-week period. Fortunately, unlike the September 16-18 event (when four died), it appears that, so far, no known fatalities have occurred with the storm in Montpellier.

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The storm brought this September’s total rainfall amount to 350 mm (13.78”), which is also a new monthly record (previous record being 293.2 mm (11.54”) in September 2003.

The cause of the intense rainfalls in both cases of September 16-18 and September 29 is an atmospheric set-up that is typical during the autumn in this part of the Mediterranean region (including Spain and Italy): warm, humid air flowing off the Mediterranean Sea collides with cooler dry air emanating from the Alpine region while a cold upper-air low rests over the area. Most of the greatest rainfall events in Spain, France, and Italy have occurred during September and October when this type of scenario is in play.

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