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The two "Christmas air masses" ...

The short conclusion about snow and Christmas: It has snowed in many places, in places, but it was only in the course of the 25th white (Reuss Valley, Lake Walen, Sargans, Chur region). In the north-west Switzerland, however, on Saturday morning quite common 15 cm fresh snow measured. In the Central Plateau there were 3 to 13 cm, especially in the very deep layers of the Central Plateau, the snow cover in many places thin. Today it snowed, especially in the north of storage locations in central Switzerland to Alpstein, this time with as moderate intensity. Details on the snow on Christmas Eve's at MeteoSwiss .

The prevailing weather situation, particularly the air mass origin show some interesting details:

96-hour back trajectories ("Origin of the air mass")
today (25.12. 2010) Noon, blue: air mass at 4800 m,
red: air mass at 2300 m. Source: NOAA Hysplit
include for the temperature analysis, the colors
actually the other way around ...;-)

been incorporated in the northern Alps below about 3000 meters of cold air has its origins in southern Finland (Polar Air) . Above came from about 3500 meters from the south Subtropenluft in the Alps. This is drawn in an arc from Morocco to the Azores, the western Mediterranean and northern Italy to us (see picture above). Looks like a perfect counter-current situation (see here or here), only: The flow in the amount was not very strong (visible at the short distance between the blue rectangles over northern Italy and the Gulf of Genoa ...). Accordingly, the Aufgleitniederschläge were not very strong, otherwise it would be the perfect heavy snowfall location for the northern Alps have been ....

on the radio sounding of Payerne are mentioned air mass differences can be seen nicely:

Radiosonde Payerne, 25 12.2010, at noon. Left red curve dew point temperature curve right
(The closer the lines are together, the more humid the air is
). Quite right, the wind speed and wind direction are given
(bottom Bise above all weak
Southeast wind). Source: MeteoSwiss

But the stations have confirmed this conclusion: It was not even noon today, for example, at the Jungfraujoch (3580m) at -10 ° C as cold - in the Jura mountains (about 1600m ), however, -12 ° C were measured and on the Säntis been registered -15 ° C.

The aforementioned cold air accumulated with a pressure of 15 mb in the northern Alps and caused the main Alpine ridge and south of the Alps a gusty north wind. This was, however, felt only below 2500 to 3000 meters, with gusting 50-75 km / h. Above this layer, it was slightly windy. At the Jungfraujoch (3580m) or at Corvatsch / GR (3305m) blew (as in the radio sounding), a slight southeast wind:

wind speed, wind direction, wind gust in kt and cloud cover,
25th December 2010, 13h GMT

Despite North wind there was on the Southern Alps no sun. On the contrary, it temporarily in many places a few drops of rain, the influence of the near lows over the Gulf of Genoa was too strong.