Hoarfrost and Inversion in Austria Print
Written by Helmut Hudler   
Wednesday, 26 December 2007

Northern flanks of Hohe Wand with a view into the Piesting valley
Northern flanks of Hohe Wand with a view into the Piesting valley
When cold air has blown in from the polar region, and when it has snowed and snow is covering even the plains, and when the air pressure has risen and a large high pressure zone is evident in large regions of Europe: this is the situation when temperature inversions occur regularly. Cold air is collecting in the basins of the valleys. Mist is formed which covers deeper areas and often is very stable: the sun cannot warm up the ground to dissolve the clouds, and the clouds have a much higher albedo (sun ray reflectiveness) than the ground. If the ground is then cold enough, the temperature does not rise above zero all day, and the moisture of the clouds is condensing as ice crystals on all plants, be it trees, grass or whatsoever – hoarfrost is formed.

The temperaure stratification is so stable, that if a warm weather front with rain comes bringing not enough wind, it glides over the cold air and the rain is poured through and cooling down on its way through the mist.  However, if cooled water is not stirred a bit when falling, ice crystals are not formed - but form immediately when splashing on the ground, covering everything with glassy ice - nice to look at, but a devastating situation for traffic and even trees which sometimes break under the burden of heavy ice. Usually, this situation is resolved within a few hours or two days at maximum. See the related links on freezing rain for some good explanations and pictures.

Thick hoarfrost
Thick hoarfrost
Austria was seized by such a situation in the second half of December 2007 when there was a temperature inversion and hoarfrost. On the 14th, it was snowing heavily, and immediately afterwards,  the mist was formed. It stayed stable till now (December 30th, 2007) for more than two weeks.

The walk begins in dense fog
The walk begins in dense fog
It was really dark down below, but Schneeberg webcam showed me that the upper regions of Hohe Wand were free of cloud. So, on December 20th, I started from Dreistetten, first walking through dense mist with everything covered in hoarfrost, then above the mist up the forested slope to that gorgeous viewpoint on a rock near one of the small lodges on Hohe Wand, Herrgottschnitzerhaus.

The Rosalia mountains are coming up like islets in the sea of clouds
The Rosalia mountains are coming up like islets in the sea of clouds
From there I had a really fine view over the clouds which were covering all of the landscape, with the exception of some mountainous regions popping out like islands. Up there, of course there was no hoarfrost, and the temperature was much higher.

After a short detour a bit up the plateau of Hohe Wand, I returned back down to the valley, just to find out that the uppermost grassland on the foothills were now free of mist, giving a gorgeous view to the hoarfrosted mountains.

One week after, on December 27th, I repeated this walk. The mist, now having permeated for two weeks, had vastly increased the amount of ice everywhere, with needles in big clusters, up to 2 inches long.

You could not even see the branches which were hidden by the ice crystals.

Hoarfrost covers the trees completely
Hoarfrost covers the trees completely
Hoarfrost engulfs this dogrose
Hoarfrost engulfs this dogrose
Huge hoarfrost crystals
Huge hoarfrost crystals

The mist was a bit higher up this day, so no islands of mountains could be seen.

Two good, though short, walks, each about 2 hours with 400m of ascent.

You can see more photographs on Helmut's website:  first Hohewand walk 20/12/2007 and second Hohewand walk 27/12/2007.

 




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