Two dust clouds, one from northern Africa and one from Central Europe, travelled north towards Iceland and Greenland in late April 2019.
After the exceptional droughts in 2018 (see case study A summer of heatwaves and drought), which caused a lot of damage to agriculture and forests, the start of the 2019 vegetation season in Central Europe was very dry. Winter 2018/19 did not bring enough rain to allow the countries to recover from the earlier water deficit.
At the beginning of April 2019, in parts of Germany and Poland, extreme drought conditions were measured. As a result, on 22 April, with an increasing pressure gradient over eastern Germany, the German Met Service, the Deutscher Wetterdienst (DWD), issued an unusual warning of the possibility of dust storms in north-eastern Germany the following day.
On 23 April some local dust storms were observed in Germany, causing visibility problems, but they were difficult to see on any satellite imagery. However, considerably more dust was raised from the extremely dry soils in Poland, which could be well observed on Meteosat-11 images, as seen in Figure 1.
At 09:30 UTC on 23 April considerable amounts of dust were also raised over Denmark and southern Sweden. Both dust clouds, from Poland and from Denmark, travelled to the North Sea.
Outbreak over Poland
On 23 April the weather in Poland was affected by a blocking high over north west Russia and a a low over western Europe (Figure 2), which caused strong winds over Poland. The maximum wind speed recorded was reached 48 km/h (26 kts) and highest wind gust was 78 km/h (42 kts).
The dust outbreak over Poland started at around 06:30 UTC, following the breakdown of the nocturnal temperature inversion, as shown in the animation of the Meteosat-8 24-hour Microphysics RGB imagery (Figure 3).
Figure 3: Meteosat-8 24-hour Microphysics RGB animation, 23 April 06:00–12:00 UTC
Under normal circumstances these wind speeds would not have been exceptional, but combined with the months of lack of rain and the very dry soil, they prompted this unusual event. In fact it was so unusual that many people thought the dust had come from the Sahara — a more usual occurance — especially as other parts of Europe were being affected by Saharan dust. However, what people in central and northern Poland were experiencing was the strong winds blowing the very dry soil from fields causing a significant reduction of visibility in many places, especially in north-western Poland.
Even experienced forecasters at the Polish weather service (IMGW) stated this was the first time they had observed this phenomena over such a large area. As a result some forecasts were updated, to highlight the fact that there was a significant reduction in visibility due to the dust.
Dust was also visible in the solar channels — the Meteosat-11 Natural Colour RGB (Figure 4) and the Aqua MODIS True Color RGB (Figure 5). But mainly over the water surfaces which serve as a ‘black background’ to the dust that is aloft.
Figure 4: Meteosat-11 Natural Colour RGB animation, 23 April 03:00–18:00 UTC
The brighter white plume in Figure 5 corresponds to smoke from fires, while the dust is more of a brown colour (the tone is also dependent on the soil's composition).
Fortunately, this event did not affect any airports, but because it was so unusual there was a lot of discussion in the media and on social media, with professionals being called on to explain the situation. It also gave rise to discussions about climate change and the increase in the frequency of droughts in Poland.
Saharan dust outbreaks
At the same time as the dust outbreak over Poland a different dust cloud, raised by a cyclone over the Western Mediterranean, was travelling from North Africa to western Europe. The "African dust" could be easily seen on the Dust RGB from 22 April (Figure 6) and on the early morning HRV Cloud RGB image (RGB HRV, HRV, IR10.8) from 23 April (Figure 7). The granular structure of the cirrus clouds over France is a clear sign of dust aerosols inside the cirrus clouds.
HRV Cloud RGB
A day later, on 24 April, both areas of dust, the dusty cirrus from the Sahara and the Poland/Denmark dust cloud, could be seen over the North Atlantic and the North Sea, respectively, as seen in the Meteoesat-11 HRV image (Figure 8). From there, the dusty cirrus cloud travelled onward towards Iceland and Greenland.
The granular cirrus cloud exhibited a peculiar signature in CALIPSO/CALIOP: strong (bright), concentrated, continuous lidar backscatter over 300 km long (Figure 9). This dusty cirrus cloud continued its drift north and showed up again in the lidar over northern Greenland on 25 April (Figure 10).
Latitudes and longitudes of locations along the CALIPSO ground-track (lower figure) are given below the image. Source: NASA
"Sandstorm on the road". Strong wind and IMGW warnings (TVN Meteo)
Blowing dust in Śliwice, Kuyavian-Pomeranian, Poland (Kamil Prabucki/Severe Weather EU/Twitter)
Another view of 'dust bowl' in Poland yesterday (Grzegorz Zawiślak/Severe Weather EU/Twitter)
Previous case studies
Cellular convection in cirrus clouds (11 Feb 2010)