A downburst among the Alps.

AlpinLuke

Forum Staff
Oct 2011
27,185
Italy, Lago Maggiore
I've collected information about this atmospheric event and it seems it's really rare here. Anyway a couple of days ago I faced a downburst and it was like to face a hurricane.

The mechanism is simple: a very wide and heavy mass of clouds, with high density and ice, passes the mountains to reach the zone of the lake ... that incredible mass of clouds falls down [it's gravity, you know] and this forces the air at ground level to accelerate in a dramatic way. I have faced a ground wind around 200 km/h [that's a hurricane].

What I can say about this is that the twister of some years ago was less violent. Straight winds are well more dangerous that twisters [trust me about this]. We've got secular trees here in Verbania and they simply made a joke of the twister, but some of them haven't been able to resist to the downburst.

Personally I was walking through the forest when I saw a dark blue wall of clouds above the mountains. My experience told me that I was going to be in serious troubles. But an Alpine downburst lasts for 10-15 minutes, no more. So that I found a refuge and I waited.

It was really violent. More violent of the one in 2009.

On internet I've seen that someone has posted videos on Youtube saying that a twister hit my hometown. No, that's scientifically wrong: it was a downburst, not a twister.

 

Ichon

Ad Honorem
Mar 2013
3,708
Downburst isn't extremely rare but very large downbursts are relatively rare for the correct airmass carrying that much water to meet the right terrain from the right angle to get lifted overtop with most of its water capacity untouched and then for the terrain to drop away on the other side in just the right way.

I was swimming in a river a couple weeks ago when a high altitude thunderstorm passed by very quickly (Colorado river around 3000 meters altitude) and a lightning bolt hit the side of the canyon that the river cuts thru about 1/2 mile away from where I was swimming. The electrical current was palpable but the flash and boom between the canyon walls was incredible. For a second I thought I had actually received much closer direct hit the flash, charge, and boom were simultaneous, unlike all the other lightning strikes I have observed from further away.

Within 30 seconds the formerly placidly flowing river had choppy waves over a of 1/3 meter and a minute of sustained wind gusts I had to hold on to the ground not to get rolled away. Most intense storm I have been in! I have seen tornadoes in Texas from less than 1 mile but other than a weird light, smell, and the obvious funnel cloud there wasn't much physical sensations unlike this occurrence.
 

AlpinLuke

Forum Staff
Oct 2011
27,185
Italy, Lago Maggiore
"Downburst" - first time I hear this category. That's interesting - mass of clouds falls down.
It was exactly what I saw: an entire gigantic mass of clouds falling down ... generating a tremendous directional wind at ground level. That's not so obvious here: usually on the South wall of the Alps in happens that wind falls down generating warm air streams [it's the "phone"], but this occurs in sunny days.

Alpine storms are well different and just yesterday we have had a typical Alpine storm. The clouds remain high in the sky, the rain is terrible and winds are strong, but not like the ones of a hurricane [like in case of a downburst], and they are not directional ... they turn ...
 

Ichon

Ad Honorem
Mar 2013
3,708
Föhn and chinook winds are interesting and rare to experience the very speed one unless you spend a lot of time on the lee side of mountains.
 

AlpinLuke

Forum Staff
Oct 2011
27,185
Italy, Lago Maggiore
Your spelling is better. Here Föhn is not so rare. Usually it comes in this part of the year or in early spring and it's quite warm. Anyway here it's not associated with thunderstorms; in this section of the Alps the winds of the storms are the "Tramontana" from North [very powerful] and the "Maestrale" from North West which is the one with the highest energy [and it was blowing in occasion of the downburst].