The precipitation maps are becoming increasingly colorful and our colleague the oracle is living up to his name with meaningful hints. Word has gotten around that something interesting is about to be fabricated in the weather kitchen. So why all the excitement?
Initial situation
We have been on the southern side of a low pressure system over northern Europe for a while now, which is bringing a south-westerly flow to the Alps. This, in turn, has ensured that the fresh snowfalls of the last few days have largely been accompanied by a lot of wind. This is occasionally evident in the usual foehn snow, on the main ridge there is a minimal trickle of snow from the foehn wall and it is generally rather mild. So far so good.
The Schapiro-Keyser cyclones
If you look to the west, you might spot a somewhat unusual-looking area of low pressure over the Atlantic. This is a Shapiro-Keyser cyclone, which means that it is not a Norwegian-type cyclone. A classic low pressure area model Norway is usually somewhat egg-shaped with a north-south orientation and the fronts embedded in the low pressure area follow a certain sequence. A Shapiro-Keyser cyclone is also usually egg-shaped, but with a more west-easterly orientation. The fronts also run differently, for example, it is typical that the cold front does not catch up with the warm front and there is no occlusion (mixed front). In this case, however, it is particularly interesting that a second wave of low pressure forms in the area of the warm front of the original cyclone, which jumps onto the strong jet and heads towards the French coast at high speed, arriving there in the night from Thursday (15.12.) to Friday.
Joachim
The small wave has it all and turns into a full-blown low: Joachim is born. In a matter of hours, it will develop from a half-strong storm into a bodybuilder with hurricane ambitions and will cause extreme winds in large parts of France and Germany on Friday (16.12.). The forecast core pressure is record-breakingly low and Joachim will be a storm chaser's wet dream. For everyone else, there are severe weather warnings from the German Weather Service and the recommendation to stay at home.
Joachim only touches the Alps, but that will probably be enough for a few exciting days. We'll leave the details to colleague Orakel, at the moment it looks like a westerly and then a north-westerly storm, neither of which is too close.
