The 12 and 13th of December 2022 were two very extreme weather days in Helsinki. The first day a true blizzard, with wind gusts over 20 m/s raged over Helsinki. The day after, the storm calmed down, but in its place came sea-effect snow. Both days saw well over a decimeter of snow, with on the latter day most fresh snow piling up. The total snow depth hovered around 45 cm at the end of the day on the 13th of December; the highest December snow depth since 2010. In this blog, we look back on these remarkable weather situations exactly one year later.
Blizzard in Helsinki
A mere 48 hours before the snow storm, on the 10th of December 2022, a low pressure system started to form over the Mediterranean, just south of the Alps on a very strong airmass boundary. Via Eastern Europe, the storm arrived in the Baltic States and Finland on the 12th of December. During the day, the winds picked up in Helsinki, and in the course of the afternoon it started to snow.
reanalysis weather chart from Wetterzentrale.de. A rapidly strengthening low pressure system approached Finland from the south.
The snowfall was accompanied by remarkably strong wind gusts in the capital/coastal region. Source map: Tuulikartta.info.
The storm’s intensity increased rapidly, with snowfall and winds picking up fast. The storm peaked already in the late afternoon. Wind gusts over 20 m/s were measured on several weather stations in and around Helsinki. A bit over a decimeter of fresh snow fell, however total amounts were hard to estimate due to the snow dunes forming. This new snow, however, fell on top of an already existing snow layer of 20-30 cm. During the evening, the blizzard kept raging, although the intensity of the winds was gradually decreasing. Check out this insane snowstorm in the video below!
Gulf-Effect Snow
During the night, the winds continued to calm down as the storm lost some of its intensity and Helsinki was located more in the core of the low pressure system. In the morning, it was again (or still?) snowing. Unlike what the weather models had forecast, the snowfall reintensified during the day, and continues bands of snow moved from the Gulf of Finland over the capital region and other coastal regions. Gulf-effect snow!
I had experienced substantial sea-effect snowfall a few times before in The Netherlands, with the 17th of December 2010 being the most remarkable event. On this day, heavy snow showers from the North Sea dropped 15 cm of snow in the region where I lived – a truly huge number for Dutch standards. I hoped to experience sea-effect snowfall once again, and this day, the 13th of December 2022, turned out to be my lucky day.
See the video of the gulf-effect snowfall on the 13th of December below. At the end of this article, you can also find a photo gallery of this extreme weather day.
Gulf-effect snow happens quite regularly over the Gulf of Finland, but rarely do these snow showers reach Helsinki. This is because the flow needs to have a southerly component for the snow bands over sea to reach Helsinki, yet cold air generally comes from more notherly regions.
Above a screenshot from radar images from the Finnish Meteorological Institute. On December 13th, 2022, snow bands from the Gulf of Finland, moved over Helsinki from the south. Gulf-Effect snow!
As the 850 hPa temperature (around 1400 meters above sea level) dropped to values around -14°C, the contrast with the still relatively warm sea surface was huge. This large temperature gradient caused a strongly instable atmosphere, and the warm, moist air from the sea surface rised (convection) to form deep clouds and extreme snowfall.
More snow in Helsinki than in Lapland
It snowed almost all afternoon, sometimes with very high intensity. The snow just kept piling up, and at the end of the afternoon, when it stopped snowing, the maximum snow depth temporarily reached up to 45 cm – the highest December snow cover in Helsinki Kaisaniemi since 2010! At this point, the snow depth in southern Finland was higher than in Lapland, a rare statistic.
Snow depth in and around Helsinki. Source map: Tuulikartta.info.
In the evening, we went to the Christmas market in Helsinki’s city center. The Christmas feeling was complete with the massively thick layer of snow covering all the stands and streets. What a day!
More info about sea effect snow and how it forms you can find here.
