Low-pressure system LOUIE
(baptized on 22/03/2019)
On 22nd of March 2019, an unnamed low-pressure area with a complete frontal system was found over the Labrador Peninsula in Eastern Canada. This cyclone was located directly in the West wind drift and was thus analysed to reach continental Europe via Greenland in the next days. Based on the prognostic map of this day, the meteorologists of the Berliner Wetterkarte named the low-pressure area LOUIE.
The following day, at 00 UTC or 01 GMT, the low-pressure system had reached the southern tip of Greenland, with a central pressure of just under 990 hPa, which is quite strong for a low-pressure area in this early stage of development. For comparison, the average air pressure at sea level on Earth is 1013 hPa. From the low’s centre, a warm front reached about 1000 km southeast into the North Atlantic Ocean, whereas a cold front extended South-West over Labrador. A few hours later, the warm front reached Iceland, beginning to cause precipitation, such as 7 l/m² of rain, snow and sleet on the Vestmannaeyjar islands in Southern Iceland in preceding 15 hours 03 UTC on 24th of March.
Cyclone LOUIE continued to move eastwards and was located over Northwestern Iceland at 00 UTC on 24th of March, at which point it possessed a central pressure of about 995 hPa. By this point, it had started occluding, which essentially means that the cold front was catching up with the warm front, forming a new type of combined front, the occluded front. This procured about 200 km across Iceland, at which point it split up at the so-called triple point into a warm front pointing in an Easterly direction over the Norwegian Sea and a cold front that curled back up on itself, ending over the North Atlantic Ocean. I the course of the day, cyclone LOUIE’s frontal system crossed the Norwegian coast, most of Great Britain and parts of the Benelux countries. The highest precipitation wase measured in the area around Trondheim, with a 12-hourly maximum of 37 mm until 7 pm in Kvithammer. At night, the frontal precipitation also reached the Low Countries as well as northern Germany; here, East Frisia was a focal point, with up to 8 mm of showery rain in 12 hours until 7 am. In exposed locations the wind reached Beaufort 12, or hurricane force, for example 150 km/h on Cairn Gorm in Scotland. However, the record on this mountain is 278 km/h, so this is by no means an exceptionally high value for this particular environment.
On 25th of March, again at 00 UTC, low-pressure area LOUIE was located over the Skagerrak, now with a weakened central pressure of about 1010 hPa. Additionally, the isobars surrounding the lowest pressure were no longer closed, which indicates a decrease of the pressure gradient to the adjoining areas. This theory is supported by the low’s frontal system, which was now fully occluded, a state that is usually the final stage in a low-pressure area’s development. Nevertheless, the cyclone continued to bring damp weather to most of Central Europe. Throughout Germany, weather stations recorded advective precipitation from nimbostratus clouds, usually considered more typical of a warm front, with a maximum of 14 mm of rain in Olsberg-Brunskappel measured in the 12-hour period leading up to 7 pm. The precipitation area also included large parts of the Alps, where, over the course of the day, the snow line dropped down to 1000 m. In 24 hours, Rudolfshütte, a weather station at 2400 m above sea level in the Austrian Alps, recorded 31 mm water equivalent of snow, leading to a total snow depth of 3 m. On mountain summits, violent storm and hurricane force gales were documented, with 122 km/h recorded on top of the Rax range in the eastern Alps.
24 hours later, at 00 UTC on 26th of March, the cyclone LOUIE had moved southeast and was found east of Kiev with a central pressure of just under 1010 hPa. A meandering cold front connected its centre with the Adriatic Sea, and in the east and west, the low was flanked by two high-pressure areas, HANNELORE and IRMELIN, which made further progression impossible. Because of the pressure gradient, gusts of up to 80 km/h were measured in Kraków, but over the course of the day, the low-pressure area LOUIE weakened further, with a diminishing weather activity. Thus, it was not marked any longer on next day’s Berliner Wetterkarte.