High Fiona is still dominating our weather at the moment, but the end of the calm conditions is already in sight. From the middle of the week, we will return to the old pattern and the weather will become much more dynamic again!
Fog and sunshine
Just like yesterday (Sunday), we can look forward to bright sunshine and plenty of blue sky outside the fog today. Below 700 to 800 meters, however, there is fog, which will only partially clear in the afternoon. The reason for this is not only the weak sun but also the pronounced inversion – and the strong temperature contrast between above and below. It is exceptionally mild on the mountains, with the zero degree limit at 3500 to 3600 meters. At 2000 meters, the values range between 8 and 10 degrees. In contrast, it remains cold in the fog soup, with temperatures usually only slightly above zero.
Fig. 1: View from the Rigi over the sea of fog this morning; Source: Roundshot
Farewell High Fiona
After a clear night, the picture will be the same tomorrow, Tuesday. There will be fog in the Swiss Plateau with an upper limit around 700 meters, apart from that the sun will shine. The weather-determining high pressure system will begin to retreat towards the Atlantic. As the air pressure drops and a south-westerly wind picks up, the chances of clearing will increase and by the evening most of the fog will have lifted. At higher altitudes it will remain sunny and very mild, with the first high clouds appearing from France and Germany during the afternoon. During the following night, the clouds will continue to increase and later a first disturbance zone will reach us.
Fig. 2: Weather tomorrow Tuesday: Once again fog in the lowlands, lots of sunshine in the mountains; Source: MeteoNews
Wet once again
New precipitation will spread with it, with the snow line between 1000 and 1200 meters at the beginning. In the course of Wednesday morning, it will fall to 800 to 1000 meters, while at the same time the precipitation will increasingly retreat to the Alps and the foothills of the Alps. In the Swiss Plateau, it will be mostly dry again by the afternoon. Some colder air will still flow in on the back of this front, but the precipitation will then subside along the mountains. In the valleys on the southern side of the Alps, a northerly foehn will develop.
Wind and new fronts
On Thursday and Friday, Switzerland will be caught between a high over the Atlantic and a storm depression centered over the Baltic Sea in the area of a strong northwesterly current. On this path, moist air will reach us in batches, which will then accumulate along the mountains. The snow line will vary between 1000 and 1500 meters. Once again, there is potential for larger amounts of precipitation, but there are still considerable differences between the models in this respect.
Fig. 3: Jet stream over Central Europe, strongest area just north of Switzerland (wind 300 hPa, Friday, December 22, 2023, ECMWF); Source: MeteoNews, Ubimet
Due to the large differences in pressure, the wind will also become a topic again, freshening to gale force. From today's perspective, we expect gusts of between 70 and 90 km/h in the Swiss Plateau, but even that is not yet set in stone. A strong northerly foehn will blow in the south on Friday. Windy and intermittently wet conditions will continue until December 24. Christmas Eve doesn't look too contemplative, at least from a weather perspective. Updates will follow here...
Fig. 4: Outlook for the coming days; Source: MeteoNews
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