It was only ten minutes during which the storm raged in the Lavanttal on Thursday afternoon – and the gusts of wind, which had deadly consequences, lasted only a few seconds. As Christian Stefan (ZAMG) said, such a weather phenomenon is extremely rare in Carinthia – within minutes there was a jump from weak wind to just over 100 km/h.
Several factors came together on Thursday, explained the expert from the Central Institute for Meteorology and Geodynamics: “In the Lavanttal, temperatures were high at 33 degrees, while a thunderstorm blew up in the west.” The system from Italy had moved eastwards via Carinthia. Strong high-altitude winds then spread through the thunderstorm to lower altitudes: “That caused the strong gusts.” The dry, hot air in the Lavanttal also led to an acceleration of the wind – while wind peaks of 70 to 80 km/h were measured in Villach and Klagenfurt, it was finally 100 km/h in the Lavanttal and then even more in Styria.
“Thunderstorm partly unpredictable”
“It is very rare that something like this occurs in Carinthia, such a front that brings these peaks in such a short time,” emphasized Stefan. Such wind speeds are hardly measured in Carinthia, the federal state is rather weak in wind. It is also possible that the wind was even stronger at certain points than was recorded at the measuring points: “It is possible that there were also hurricane values.” Fall winds during thunderstorms could ensure that there are large differences in wind speed within a few 100 meters.
It became clear on Thursday that such a thunderstorm with gusts of wind can break out almost without warning: only Upper Carinthia and East Tyrol had an orange weather warning at noon, Lower Carinthia was yellow (“only isolated weather-related impairments and/or damage to be expected”). Stefan confirmed this: “According to the assessments in the morning, most weather models have shown that there could be more intense thunderstorms in Upper Carinthia and East Tyrol.” These models would not have captured well that the thunderstorm would then move through to the east: “These are local weather models that also have their weaknesses.” If the low is 100 kilometers elsewhere, it will shift, and local effects would also make localization more difficult. To a certain extent, thunderstorms are unpredictable, says Stefan. The fact that the potential for severe thunderstorms was there was already relatively well estimated: “But it is difficult to estimate where it will then arise and fall.”
“Squall line” frequent in Upper Austria
The line of thunderstorms drawn up from the south, which killed five people in Austria on Thursday, caused a so-called gust line, described Bernd Niedermoser from the Central Institute for Meteorology and Geodynamics (ZAMG) in Vienna at the APA request, describing the special features of the storm disaster. “The cold front flowing out of the thunderstorms flowed ahead of the thunderstorm line and caused violent squalls about ten minutes before the thunderstorms.”
According to the expert, such situations often occur in Upper Austria and Lower Austria, for example, when thunderstorm lines come up from Bavaria, and they are usually easy to predict here. In the mountainous areas of Austria they are much rarer and here the amplification and weakening due to mountains and valleys are more difficult to predict. “For people outdoors, the squall lines also mean that they don’t perceive the threat of the approaching storm as strongly, since warning signals such as black clouds, lightning and thunder are even further away, while the approaching squall line is not visible and emerges extremely quickly,” like Niedermoser.
The wind forces were also exceptional: according to ZAMG, wind peaks of more than 100 km/h due to thunderstorms are very rare in the valleys of Carinthia. In the past 30 years, there have been peaks of over 100 km/h ten times in the summer months in the low-lying areas of the state, yesterday, Thursday, when in St. Andrä in the Lavanttal, where the two fatalities are to be mourned, 103.3 km / h were measured, already included. In the measurement history of the St. Andrä weather station itself, which goes back about 30 years, there were two times over 100 km/h in summer, including the most recent disaster.
At the Neumarkt (Styria) weather station, 139 km/h were measured on Thursday. This has never happened here since measurements began in 1993: The highest peak wind measured here was 100 km/h in January 2008. In Lower Austria, on the other hand, peak winds of over 100 km/h are not unusual in summer and occur almost every year at at least one measuring station before.
Source: Nachrichten
