Weather warnings for Germany now more precise than ever | Science| In-depth reporting on science and technology | DW | 14.07.2016
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Weather warnings for Germany now more precise than ever

Germany's National Meteorological Service has introduced a more precise weather prediction system. It issues storm and other warnings not only for counties, but also for municipalities and rural areas.

Southside-Festival in Germany canceled after weather warning (Picture alliance/ dpa/ F.Kästle)

A German festival in June was canceled just in time before severe weather - thanks to a storm warning

Cry "wolf!" once to often - and people will stop paying attention. In predicting weather events, meteorologists have always faced that fundamental problem: A prediction may come true in one place but not in another, even though the two places are not that far from each other.

This is very important in the case of weather warnings - like for freezing rain, which results in slippery sidewalks; heavy rain, with its danger of flooding; as well as for hurricanes, blizzards or thunderstorms.

With such weather, citizens, firefighters and emergency crews must be able to react. Citizens should avoid dangerous areas such as forests and parks, while floodplains and riverbanks must be evacuated - or people should receive the advice to simply better stay at home.

When the predicted storm is milder than expected

If a predicted severe weather situation doesn't materialize, this can even be embarrassing to those who issued the warning or took precautions.

The annual Düsseldorf carnival parade for 2016 was called off after meteorologists predicted heavy storms including strong winds. Afterward, debate erupted among citizens, organizers and politicians as to whether calling the parade off was a bit too much. In the end there were strong winds, but the storm was not very dangerous.

Generally, the German weather warning system is fairly well-suited to deal with such situations. The German national meteorological service (Deutscher Wetterdienst - DWD) has a warning system in place, which informs the public via the internet, SMS or smart phone app.

In comparison with other European countries, Germany's warning grid is highly detailed.

Screenshot Deutscher Wetterdienst Wetterwarnsystem

In Main-Kinzig County, all communities used to receive warnings (marked red) - even if they only related to local weather events

Warning only those who need it

But anything that's already good can still be made even better - which is why the DWD fine-tuned its warning system even further.

From now on, there will be not only warnings for counties - which in Germany can be rather large - but also for municipalities and rural parishes. There are roughly 400 counties in Germany - but 10,000 municipalities and parishes. In other words: The system now is 25 times higher resolution.

"We have realized that a warning on the basis of the county is to broad," meteorologist Hans-Joachim Koppert from the DWD says.

"There are counties that extend 70 kilometers [43 miles] from one end to the other. If we were to issue a warning for a thunderstorm that only takes place at the eastern edge of the county, someone who lives at the Western edge will also receive it, although they may see nothing but blue sky."

Screenshot Deutscher Wetterdienst Wetterwarnsystem

Weather warning of the future: Only the affected municipalities and parishes will be warned

The previous system was designed according to the organizational structure of the civil protection agencies - firefighters and emergency crews. Those are organized by county.

But many citizens don't know that, and could not interpret the warnings accordingly, Koppert recalls: "They then thought: 'What are those meteorologists doing?'"

Another example is an acute danger of heavy squalls high up in the mountains. A huge county - most of which consisting of lower-lying lands - may have received such a warning in the past.

But now, it only goes out to that one community that actually is located in a mountainous part of that county.

Not leaving all the decisions to computers

Hans-Joachim Koppert, Meteorologe vom Deutschen Wetterdienst

Early detection of thunderstorms remains a major challenge, meteorologist Joachim Koppert says

Calculation of weather models today is done by computers. They receive and process a wealth of information from all over the world.

But then the handwork begins: "We still need humans to do the work that really gives added value - meaning an improvement to our weather prediction systems," Koppert says.

Key to a successful and precise weather warning is the meteorologist, with his understanding of weather conditions, he adds.

And not every prediction is equally easy. "If we have continuous rain or a storm front in the winter, we are able to issue warnings as early as two days in advance. Those situations can be predicted very well," the meteorologist says.

But in the case of thunderstorms in summer, the situation may be trickier. "The atmosphere doesn't know where it will trigger a thunderstorm with lightning in about two or three hours - there are really chaotic factors at work," Koppert says.

"We can really only predict a thunderstorm once it has at least become rudimentarily visible."

Peering at the atmosphere in 3D

Nonetheless, Koppert is optimistic that even such complicated predictions will also improve in the future. Already today, it is possible to create three-dimensional pictures of precipitation in the atmosphere - using radar. The density of rain, snow or fog thus becomes visible.

Screenshot Deutscher Wetterdienst neues Wetterwarnsystem

Formerly, a wind warning was issed for the whole county - now, only for the higher-elevation towns and villages

In the future, that data could be complimented by three-dimensional data on humidity in the atmosphere. That information can be collected by GPS ground stations, which send and receive signals from navigational satellites. And those signals are very sensitive to changes in humidity.

But that technology isn't that far along yet. For now, the refined weather warning system is available for everybody at the DWD homepage. And at the beginning of August, DWD will launch a new weather app applying that new system.

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