Mild and sunny, potential cold wave in January

For over a week, the Alps have been basking in the sun, but at the beginning of January, the weather map is really going to change. As is often the case with such transitions, it remains uncertain if and when the cold air will arrive. The snow forecast map is starting to show some color again, but we still need to take the details with a grain of salt for now. In this update, I will discuss the potential as well as the uncertainties in the new year.

Possible strong cold wave in January

We have seen a lot of potential on the weather maps for days. Low-pressure systems reaching Europe are moving increasingly south, and a ridge of high pressure is developing over the ocean that occasionally extends into Central Europe. When a low-pressure system stretches over or south of the Alps, it brings snow, and polar or even arctic air may flow in from the back with temperatures of -10 degrees or lower at 1500 meters. In the ensemble of the GFS model for Innsbruck (image above), it’s clear that most calculations predict cold to very cold temperatures for the period starting January 3. The milder solutions (including the main run) do indicate that there are still some possible pitfalls.

First precipitation on 2 or 3 January

On January 2, the charts show a significant depression near Denmark. The fronts from this system will reach the Alps somewhere around Thursday evening (GFS) to Friday afternoon (ECMWF). GFS shows the cold spreading quickly with snow falling into the valleys, clearly visible on our snow forecast map (based on this model). The emphasis is on the Western and Northern Alps. According to ECMWF, a weak depression develops over France, causing the cold to reach the Alps a day later. In that scenario, rain may fall below 1500 meters initially.

Repetitive situation

High-pressure impulses over the ocean remain active for a while. Later in the first week of January, more depressions will likely move in from the west. Each time, the direction and depth of the disturbances will determine snowfall and temperature in the Alps. We also see solutions that are cold but allow little snow due to the influence of high-pressure extensions.

Course of depressions determines the weather

On the east and south side of a depression, we find the so-called warm sector where precipitation falls as rain up to considerable heights. When a depression extends south of the Alps, we are not affected. However, when the trajectory is more northerly or a depression lingers to the west of the Alps, this can slow down or even completely block the outflow of cold air. The images above show the forecast for Monday night (January 6) from the ECMWF and GFS models. ECMWF shows a (weak) low-pressure area near Portugal with the Alps in deep winter conditions. GFS (second map) expects the low to be deeper and more northerly, allowing milder air to reach the Alps. In that case, there will be no serious cold, and rain can fall up to 2000 meters in the Western Alps.

Lack of snow remains a concern for the Southern Alps

December will go down in the books as a fairly good month for winter sports, with reasonable to good snow cover and good conditions for artificial snow production. For freeriders, there was plenty to enjoy, especially after the pre-Christmas dump in the Western and Northern Alps. The snowfall consistently occurred in west and northwest stau situations, which meant that hardly any base has been built up to the south and east of the main ridge. In the Dolomites and parts of the rest of the Italian Alps, there is barely any snow cover even at 2000 meters. During the start of the new year, the snow keeps coming in from the west or the north. It would be ideal for the Southern Alps if a depression were to move a bit further south, or if a Genoa low were to develop due to the outflow of polar air over the Mediterranean Sea. This is certainly possible in the upcoming setup, but not yet during first snow situation (January 2-4).