How Meteosat-1 'saw' severe storm over Switzerland

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There was catastrophic rain and wind damage over the northern part of Canton Ticino in southern Switzerland on 7 August 1978.

How Meteosat-1 'saw' severe storm over Switzerland
Date & Time
7 August 1978 11:00–18:00 UTC
Satellites
Meteosat-1
Instruments
MVIRI
Channels/Products
Visible

By HansPeter Roesli (Switzerland) and Sancha Lancaster (Pactum)

To commemorate the 40th anniversary of the launch of Meteosat-1, we take a look at a devastating flooding event in Switzerland in August 1978. Meteosat-1, was the first satellite in the Meteosat First Generation series and was launched on 23 November 1977.

On 7 August 1978, heavy rains lead to severe flooding in the Alpine area of Locarno and 11 people were reported to have died. 24-hour rainfall records were broken when 201 mm was recorded in the Sopraceneri area, beating both the previous highest August rainfall record of 165 mm on 13 August 1924 and the overall 24 hour record of 181 mm on 7 October 1977.

The floods struck the local railway causing damage to almost 700 m of track, mainly on the Italian side. There were no injuries due to this, but reconstruction of the line lasted until the end of the year.

In total the damage and disruption from landslides, streams overflowing and debris flows cost the country around 610 million Euros.

Meteorological Conditions

On 6–7 August an unusually strong (for the late summer season) outbreak of polar-arctic air invaded western Europe.

The frontal system linked to this outbreak extended from Denmark to the western Mediterranean. Over the Alps it remained blocked in the afternoon/evening of 7 August.

At mesoscale level the cold air was already pushing down into the northern valleys of Canton Ticino, Switzerland (in particular the Valle Maggia), while the remaining part remained in warm humid Scirocco air.

Figure 2: Surface analysis weather chart, 7 August, 12:00 UTC
Source: MeteoSwiss
Full Resolution
Figure 3: ECMWF ERA40 analysis, 07 August, 18:00 UTC

The synoptic situation is well-illustrated by the original manual surface analysis of the local forecasting centre at Locarno (Figure 2)

This strong and stationary temperature gradient at low levels was coupled with a very dynamic upper-air situation, as shown in the ECMWF ERA40 analysis (Figure 3). A strong PV maximum (west of the Pyrenees) and a number of high winds (blue spine pointing downward from the jet stream) were present at 18:00 UTC. This resulted in heavy rain and strong winds for several hours, as illustrated by the time evolution of the Palagnedra rain gauge with 55 mm measured between 17:00 and 18:00 local time.

The rain amounts went well beyond what the region was used to dealing with. A mixture of water, mud and broken wood (approx. 1. million m3) drained down the rivers, washed bridges away (Figure 4), blocked the spillover of the Palagnedra dam (Figure 5). The openings of the spillway of the Palagnedra arch gravity dam were clogged by a tremendous quantity of driftwood, 12–26 m thick.

The mass of water finally ended up in the Lago Maggiore. The lake level rose by a record-breaking 170 cm in a few hours and inundated surrounding areas, including the town of Locarno.

Figure 4: Washed away Moghegno bridge in Valle Maggia. Source: Eco di Locarno newspaper
Figure 5: Alluvial wood filled reservoir at Palagnedra dam. Source: Eco di Locarno newspaper

At the time of the event the forecasting office of Locarno did have some polar satellite imagery available, but it was not good enough to follow this fast event. Imagery from Meteosat-1 was not yet available locally.

Figure 6
 
Figure 6: Meteosat-1 Visible image, 7 Aug 11:00 UTC. Source: DWD Museum

A reconditioned imagery from the DWD Museum shows the cloud situation at 11:00 UTC (Figure 6) and 12:00 UTC (Figure 1, top right of page, click to expand) and gives an idea of what happened.

The red arrow on Figure 1 points to the area of interest and a 'kink' in the white cloud mass. This kink probably shows the effect of the Scirocco winds that blew from the Adriatic Sea into the Po Valley and held back the frontal system for a few hours.

 
 

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