Polar low 6th of February 2012

On the night to monday 6.th of February 2012 there was a rare case of a small polar low in southerly flow northeast of the east Finnmark coast. The events leading up to the development were partly a long spell of clear and cold weather in northern Scandinavia, giving temperatures down to -40°C inland and less than -20°C at the coast. With southerly winds, this gave a severe cold air outbreak from the Finnmark coast and the Kola, clearly seen from the picture as cloudstreets streaming out the fjords in the area. Picture 1, shows a cold air outbreak and a small polar low off the coast of Kola

Also, a cold upper low gave a temperature difference of approximately 48°C between the sea surface off the Finmark coast and the air at 500hPa. At the same time, a weak surface low with an associated frontal zone was forming over the White Sea Area, moving northwards out over the southern Barents sea. In contact with the warmer sea surface, the air colomn was destabilized, and the low intensified, giving 40kt winds (from ASCAT 12,5km data) in the eastern side of the low. The low then moved northwards and subsequently dissipated over cooler waters in the northern Barents sea. Picture 2, shows the situation at 500 hPa at the time of intensification. Green lines is the Z500 geopotential. Blue or red dotted lines are the temperature difference between the surface and 500hPa.

Model performance of the Hirlam 8km was initially good, but as is typical, the position of the low was forecast closer to the main synoptic center with time. At 9 hrs prognosis, the model position of the low was 115km off to the west, but the wind was correctly given with the same magnitude as the observed 40kts from the ASCAT. Picture 3, shows the comparison of the Hirlam 8km prognosis at +9 hrs compared to the satellite images, showing that the low is forecasted about 115km closer to the synoptic center at this time.

Picture 4, shows model wind above 35kts, with maximum at 40kts. Apart from beeing offset in position, the magnitude in the wind is correct.