My brother, who lives in southwest France wrote to me the other day about a strange experience. So here’s his words and your thoughts will be appreciated.
“It was getting on for 7pm (on 30th March) when I drove home from town (Riberac) and still nicely light with some weak sun shining from the west (where else!) As I drove out of town I was heading west for five minutes and then turned 90° in a southerly direction directly towards home. (As I've often mentioned) I live literally on top of a hill which is surrounded by valleys and a very large flat agricultural area which spreads away towards the north and the west. Well, it was through this flat area that I was now travelling. At the moment there's very little growing in the fields but they have all been ploughed so it appears to be quite an immense area and you can see for miles.
At first I didn't notice but soon realised that, although the sky all around and down to the horizons was light with the sunlight reflecting on distant white clouds, overhead was the most enormous black cloud, miles bigger even than a Vogon Constructor Fleet ship, that seemed to be almost stationary. The sort of black that could not even reflect light back. I was so amazed by this sight that I actually stopped my van and just sat there marvelling at this 'object'. It had also started to rain, great big blobs of the stuff not at all like raindrops and that reminded me that Meteo France had very recently mentioned the possibility of 'orage' which is thunderstorm and possibly hail.
When I returned home I checked on the weather radar to see if there was any rain due. There wasn't and there was only one area of rain on the map which was more or less round and corresponded exactly with the cloud I had watched. So I pulled out on the radar and there wasn't another area of rain in France apart from along the North coast and a couple of small patches towards Paris.”
So what caused that small ‘blob’ of cloud and rain? It was divorced from all other things such as fronts, depressions or even hills. I guess that the low sun added to the depth and darkness of the cloud, by the way. Personally I suggest that it was a small eddy in the pressure that created a mini-depression but I’d be pleased to hear someone else’s thought – especially someone who knows about weather.
PS Sorry his screenshots come from another weather site!
Probably makes sense I have a German weather thread here!
I can only speak for East Germany, specifically Berlin but overall it has some similar themes to the UK climate except hotter in the summer and colder in the winter. Generally it is dry except during the summer when we get rain from thunderstorms. It can be changeable and cool even in summer when we get a NWly or Nly wind. We can get some very high temperatures in summer and in general it is far warmer than the UK - especially compared to my old home of Nottingham. It is definitely sunnier than the UK with us mostly missing out on Atlantic weather systems (although not all the time).
Winters are colder but snowfall is not that common as it is very dry. You can get some very low temperatures sometimes although it doesn't normally last very long. Low cloud is very common November-January and you can go weeks with no sunshine and temperatures hovering around -1 to 2c. Pretty dire and no wonder the summer-winter mood contrast in the city is so extreme. Once into late Feb the sun can burn off the cloud and dry, sunny weather is common.
This summer has been changeable during June & July with some cool & damp sub 15c days under NWly winds but also some extreme heat with our hottest day being just shy of 40c.
August has started hot and is set to remain so with maxes around 28c-35c for the foreseeable future. Friday we're expecting 38c before a 'cool' off to 32c on Saturday.
Smog in Paris
During the last few days, a few cities in France have been suffering from high levels of smog. The problems are the highest in Paris, where unhealthy levels of air pollution are being reached. Therefore, the government has decided to give free access to public transport and introduced alternative driving days [i.e. half of the cars (even numbers on the license plate) are allowed to drive on one day, while the other half of the cars (odd numbers on the licence plate) are allowed to drive on the day afterward].
From the BBC:
The full article can be found below:
Putting the values in perspective
Yesterday, critical levels of PM 2.5 were exceeded in Paris. PM 2.5 is a measure for air pollution, defining the concentration of aerosols with a diameter smaller than 2.5 micrometre. The maximum level of PM 2.5 reached yesterday was 193 micrograms per cubic meter in the centre of Paris. When the concentration of PM 2.5 exceeds 150 micrograms per cubic meter, conditions could become dangerous for human health.
The classification index for PM 2.5 can be seen below:
The PM 2.5 values in Paris (various stations), as well as other air quality variables, can be found in the link below:
Of note is that the high levels of PM 2.5 reached in Paris are very common in China. Many cities there rarely have values of PM 2.5 below 100 micrograms per cubic meter. This doesn't indicate, though, that values like this should be common in Europe as well.
The PM 2.5 values of different cities in China can be seen below:
The source of the persistent smog in France is persistent high pressure over Western Europe. Due to this high pressure, there is very little flow over France. This persistent lack of flow causes most of the air pollution that develops over Paris simply stays at the same place. For example, check the GFS chart of the wind forecast of today 12Z below:
GFS 10m average wind (12Z run)
What can be seen is that the average wind near Paris during the day is around 10 kt (20 km/h). This is not enough to clean the atmosphere around Paris.
A more important cause of the air quality problem might be the stable boundary layer which is caused by the persistent high pressure. Due to the nocturnal cooling near the surface (combined with very high temperatures at about 1000 meter height), a strong inversion (increase of temperature with height) becomes established. Because of this inversion, there is very little mixing of air (convection) in the boundary layer during the night. As a result, the pollution stays near the surface.
During daytime, it takes a very long time for the inversion to be cleared (sometimes it lasts the whole day), and therefore, the air pollution has very little time to be mixed out of the surface.
The inversion strength during daytime can be seen in the Skew-T diagram of La Trappes (close to Paris) below:
Sounding of La Trappes as of 12Z (12 UTC, 13:00 local time).
To keep things simple, only focus on the temperature line (the righter most fat black line) at the lowest levels of the atmosphere. What can be seen is that the temperature increases with height at around 800 meters. The increase in temperature is about 2*C (read the temperature by tracking various points at the temperature line by the blue skewed lines of equal temperature). Though this is not a very strong inversion, it is rather unusual that such an inversion is still apparent during the afternoon in Spring. This also indicates the inversion must have been much stronger at peak strength.
The forecast from GFS indicates that flow might be increasing in about 5 days when a trough digs southward just to the west of France. Hopefully this will mark the end of the bad air quality conditions in France.
Finally, any remarks/additions on the post are always welcome!
http://www.airinfonow.org/html/ed_particulate.html http://www.bbc.com/news/world-europe-26599010 http://weather.uwyo.edu/cgi-bin/sounding?region=europe&TYPE=GIF%3ASKEWT&YEAR=2014&MONTH=03&FROM=1612&TO=1612&STNM=07145 http://www.wetterzentrale.de/topkarten/fsavneur.html
Hello, my name is Oana Liviu, from Romania. I am currently studying GIS at West University of Timisoara (master degree), and my project is about implementing the WRF-ARW model over Romania and surrounding countries ; the link for the project is here : http://wrf.devip.net (experimental).
Currently I am limited by a weak server configuration and I started a donation campaign to raise some funds for acquiring a performant server configuration for hosting the WRF model. My goal is to improve numerical weather forecasting, by implementing higher resolution digital elevation models, landuse and lancover data, developing severe weather indices, expand the forecast area to SE Europe (maybe entire Europe at lower resolutions).
I am currently a founing member of Romanian Association for Monitoring Severe Weather Phenomena : http://rometex.wordpress.com and the implementation of the WRF model is crucial for chases and case studies.
I came to this forum to ask if anyone is interesting in donating some money to this research project. If you like to help, please leave me a Private Message.
If this message may be considered innapropiate tor this section, I kindly ask the moderators to move it or delete it.
Thak You !
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