Photo by Andre Furtado on Unsplash

Written by 08:00 English Edition

Snowstorm in Poland? Spectacular, severe and extremely rare

Janusz Zieliński
IMGW-PIB, National Meteorological Protection Centre

In the cold season, thunderstorms are an exceptional phenomenon. However, there are weather conditions so dynamic that they favor the evolution of well-developed Cumulonimbus clouds and the occurrence of atmospheric discharges also in winter. Such conditions occurred in Poland on March 26, 2019, when the active low and the cold front were moving fast through the eastern voivodeships. Strong  wind gusts, heavy snowfall and numerous atmospheric discharges were a real danger. They paralyzed in many places traffic on the roads, among others. The analyzes of the radar and measurement data of the IMGW-PIB show how rapid and sudden the development of these phenomena was.

In winter, as in summer or spring, Cumulonimbus clouds develop under conditions of thermodynamic instability and a steep lapse rate, i.e., a rapid temperature drop with the height. In the colder months, such circumstances occur most frequently on active cold fronts, followed by cold air. If lightings are accompanied by heavy snowfall, it is a snowstorm.

Sytuacja synoptyczna w Europie, 26.03.2019, godz. 12 UTC
Synoptic situation in Europe, on March 26, 2019, at 12 UTC;
the blue colour indicates the cold atmospheric front over northern Poland.

A cold atmospheric front entered Poland from the North in the afternoon on March 26, 2019. The development of deep convection was also supported by the conditions prevailing in the higher layers of the atmosphere, where an active trough of low pressure expanded. It deepened as the front moved over central Poland, which led to air suction from low to high and the formation of storm clouds. In addition, a jet stream formed in the troposphere, which contributed to the intensification of the phenomena.

The events on the front intensified,  forming a linear convective system (a squall line) over time with numerous discharges and gusts of wind up to 25 m/s (90 km/h).

Zatoka niżowa widoczna na powierzchni izobarycznej 500 hPa (około 5,5 km) oraz prąd strumieniowy na wysokości około 9 km (linie żółte)
Through of low pressure visible on the isobaric surface of 500 hPa (about 5.5 km) and a jet stream at the height of about 9 km (yellow lines); March 26, 2019, 15.00 UTC (source: www.eumetrain.org).
Wyładowania atmosferyczne wykryte przez system Perun w godzinach 07:00-19:00 dnia 26.03
Atmospheric discharges detected by the Perun system between 07:00 and 19:00 UTC on March 26, 2019.

As the front traveled, there was advection (inflow) of cold, arctic air accompanied by the rapid decrease of the isotherm 0°C (in many places below 300 m above sea level), which led to snowfall. At places, especially in Mazovia and the Lublin Region, rainfall was intense. It caused enormous road traffic obstacles. According to the Government Security Centre, 222 interventions related to the removal of the effects of strong wind were recorded (most in Mazovia – 57, Lublin Region – 27, and Silesia – 23). As a result six people died in four road accidents.

Warszawa w czasie burzy śnieżnej, 26.03.2019
Warsaw during a snowstorm on 26 March, 2019.

In Poland, there are several days during which Cumulonimbus clouds reach dimensions that allow for the generation of single lightings, especially in the coastal area almost every winter. In recent years, the strongest snowstorms in our country occurred in December 2013 and were associated with a deep and active Ksawery low. Similar phenomena also appear occasionally in other parts of Europe, Asia, and North America. They cause major difficulties, e.g., in urban traffic, and contribute to severe losses in the energy infrastructure. It shows that snowstorms are an element of the weather that is difficult to forecast.

Animacja z radaru w Legionowie z widocznym rozwojem linii szkwałowej oraz nasilaniem się opadów w czasie jej przechodzenia przez północno-wschodnią Polskę
Animation from the radar in Legionowo with a visible development of the squall line
and the intensification of precipitation during its passage through north-eastern Poland.
Prognoza położenia izotermy 0°C wg. modelu Arome. Zdecydowany napływ arktycznego powietrza spowodował śnieżyce w wiele miejscach wschodniej Polski
Forecast of the location of the isotherm 0°C according to the Arome model.
The strong advection of arctic air caused snowstorms in many parts of eastern Poland.

Main photo: Andre Furtado | Unsplash

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