WeatherBlog 6 2024/25 | Christmas turbulence

Great weather regime

The weather-wise active Atlantic is also reflected in the ECMF weather regime probability graph. Wetterlagenwahrscheinlichkeitsgraphik is an approximate translation of "weather regime frequency ensemble forecast" Graphik and we use the word here primarily to challenge the automatic DeepL translation for PowderGuide in English with a German composite!

In any case, we see a strong tendency towards the "ATR" - Atlantic Ridge - and NAO+ patterns in the weather situation probability graphic at the moment and for the next few days. NAO is the North Atlantic Oscillation and the NAO index is positive when the Icelandic Low and the Azores High are both strong. The resulting high pressure difference over the North Atlantic produces the westerly flow and therefore often humid, mild westerly to north-westerly weather in Central Europe. "ATR", on the other hand, refers to high pressure over the Atlantic, which extends relatively far to the north and thus also displaces the Icelandic low that we would need for NAO+.

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500hPa geopotential and surface pressure, northern hemisphere, GFS forecast for Thursday. Zonal flow with small waves over the Atlantic. A low pressure system will touch the Alpine region from Thu. to Fri. and bring some snow.

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Outlook

Translated into Alpine weather, the weather situation probability graphic tells us that the high pressure (ATR) of the last few days will change to more turbulent "westerly weather" (NAO+) from today (Wednesday). Not much will happen today, the rather mild air will stay with us and it will gradually become cloudier. On Thursday, we will feel an approaching area of low pressure (also shown in the graphic above right) in the form of a Föhn wind in front of the trough, i.e. a southerly flow east of the trough axis, and a subsequent change in the weather with precipitation and a falling snow line. The trough axis moves from west to east and everything happens accordingly (first Föhn, then precipitation) first in the western Alps and then with a time delay in the east. On Friday, it will remain widely cloudy, quite windy and quite cold. Saturday will bring a brief intermittent high and is expected to remain dry with a relatively friendly weather character.

Weather situation probability graph: Daily probabilities for four "weather regimes" and a gray intermediate solution that cannot be clearly assigned. In addition to NAO+ and NAO-, there is Atlantic Ridge (ATR) and "Block" (blocking high over Scandinavia).

Snow under the Christmas tree

It will be interesting again from Sunday. It currently looks like there will be heavy precipitation, with a low snow line at first and a rising one from Monday/Tuesday. We are hoping for a substantial supply of snow at least for the high and middle elevations and would like to avoid the traditional Christmas rain event at >2000m this year. Supplies currently seem likely, and rain is within the realms of possibility. We take the liberty of exclusively quoting a personal message from the oracle: "There should be an alarm at the weekend. Still questionable for Friday. So-Di quite certain."

For the Christmas holidays, the crystal ball then sees a significant moderation and high pressure pushing in from the west. The questions relevant to skiing are probably how quickly it will get warmer between Sun. and Tue. and how much of the precipitation will arrive at what altitude and in what aggregate state.