Wintry weather returned to parts of Central Europe in early May 2019, thanks to cold polar air plunging south.
By Ivan Smiljanicv (SCISYS)
During the late hours of 4 May lee cyclogenesis took place at the western edge of Alps. The initial cyclonic rotation quickly intensified over the bay of Genoa, accelerated by the rear-side inflow of the cold air that was moving across France. The system turned into a cut-off low cyclone that moved eastwards over the Adriatic Sea.
Almost in parallel, roughly half a day later, a similar dynamic process happened over the Norwegian mountains in Northern Europe. This system wasn't as intense due to a less baroclinic situation, embedded in an already well pronounced cold sector.
Both low pressure systems are annotated by a red letter ‘L’ in Figure 1 (top right, click to expand).
The trigger for both systems was a strong advection of cold polar air that was plunging southwards over Central Europe.
This cold mass of air appears is the blue area on the animation of the Meteosat-11 Airmass RGB imagery (Figure 2), with embedded cumulus fields which are the yellow areas.
Figure 2: Meteosat-11 Airmass RGB animation, 3 May 12:00 UTC–6 May 12:00 UTC
Such an intrusion of polar air brought wintry conditions to parts of Europe, with reports of heavy graupel, snow showers and frost. In France the plunging temperatures broke records for May, tens of centimetres of fresh snow fell in the Balkan mountains, and there were severe frosts in central and northern Europe.
Parts of Germany receive a sprinkling of snow in May (euronews)
Cold May weather in France breaks 50-year records (The Connexion)
Mountains of Snowdonia dusted in snow as May bank holiday temperatures tumble (North Wales Live)
Snow in May: It's all white in Bosnia, the temperature is not going over 5 degrees (VIDEO) (Telegraf)