WeatherBlog 5 2021/22 | Is the desert heat coming after the bomb cyclone?

The bomb cyclone!

Causes very uncomfortable conditions in the British Isles. Regionally, there may be a chance to get snowed in at the pub or spend the night at IKEA. For us in the Alps, let's get this out of the way right away, the bomb cyclone is far less dramatic. We are merely being grazed by a low pressure area, which is also determining the weather character in the Alps today.

Low pressure area Barra deepened by around 50hPa west of Ireland from Monday to Tuesday, so it has become stronger extremely quickly. From 24hPa in 24 hours, one speaks of a so-called "bombogenesis" or "bomb cyclone". The hurricane depression already raged in Ireland and the British Isles yesterday. It is continuing there today and at least one of Barra's fronts is arriving here. As is often the case with lows over England, the eastern Alps in particular will initially be affected by a foehn-like southerly current. The further east, the longer the Föhn will last. It has been snowing in the western Alps since the early hours of the morning. The warm front will gradually work its way eastwards today and should bring precipitation at least as far as the Arlberg during the course of the day. Further east it will snow during the night and tomorrow. Thanks to the development of low pressure in the Mediterranean, the south will also get some today and the congested areas in the IT/SLO/AT border triangle will even get quite good weather. The latest alert has more details. Thursday will also be mixed, this time with more clearing and maybe even a few hours of sunshine in the west, while the east will remain mostly cloudy.

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Barra in yesterday's satellite image. — Barra in yesterday's satellite image
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ZAMG

The outlook

The near future doesn't look too bad in terms of snow, as the oracle has already announced. It will remain relatively cold and the next front is approaching on Friday, bringing supplies for the western Alps. Little is expected to arrive in the east.

The weather will calm down at the weekend. On the southern slopes of the Alps, it should be sunny more or less all the time, while in the north, clouds will hang around for longer, especially in the eastern half, and a few flakes will still fall here and there. Much milder air masses are approaching, which will probably reach the Alps on Sunday or Monday, although the models still disagree on the details. However, the warming and the change in the general weather situation are relatively fixed. The jet stream is fairly zonal over the Atlantic, the days of the heavily clouded Azores High are over. The polar front is far to the north, so we won't get mild, humid westerly weather either, but rather high pressure with fairly warm temperatures.

500hPa geopotential and ground pressure, GFS, for today, Wednesday, and Monday, 13.12. — 500hPa geopotential and ground pressure, GFS, for today, Wednesday, and Monday, December 13
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meteociel.fr

Miscellaneous

A look at the weather station on the Pitztal Glacier still shows more or less average snow volumes for the time of year and the station location. You can now clearly see that the green curve (current season) is strongly characterized by individual snowfall events, which briefly provide above-average amounts of snow. However, the values quickly fall back to a much lower level with the subsequent settling. The black curve shows the average over the entire time series; the short-term fluctuations of individual snowfall events are "averaged out" here. Once again, we see that it is not so easy to determine exactly what "normal snowfall" means.

MeteoSwiss provides here an informative and detailed text on the correct interpretation of probabilistic precipitation forecasts, such as those offered by MeteoSwiss. The ZAMG reports a "relatively normal November" with "punctual snowfall". It would be nice if it continued like this.