Finland 30th of December 2010

 

Over Southern and Middle Finland there was widespread moderate to heavy freezing drizzle, which caused harm not only to aircraft but also to road traffic by freezing windscreens and road surfaces.

At 12.20 UTC a pilot reported moderate icing in the vicinity of Tampere airport (EFTP). One METAR reported weak freezing rain and another one snow grains, both in the Åland Islands.

The synoptical analysis shows two occluded fronts that slowly approached each other:

Fig. 5.11. Significant Weather Chart for Western Finland 30. Dec 2010 at 12 UTC by FMI. Radar locations are marked red, the Jokioinen sounding station green and the EFTP Airport blue.

The sounding in Jokioinen at 12 UTC shows a nearly neutral layer of 100 % humidity between 970 and 820 hPa. The temperature varies between -12°C and -9°C, with two small inversions. The soundings from the previous day were rather similar, but not as humid. The cloud thickened and in the end it began to precipitate.

Fig. 5.12. Sounding from Jokioinen 30. Dec. 2010 at 12 UTC

 

Satellite images


1. Meteosat, MSG instrument

Thick water clouds can be clearly seen in the 24hMicrophysical combination, where they appear orangish yellow. Clouds with small particles appear greenish, so they are potentially less icing than yellow clouds. Generally, large drop HRVFog is of no use at this time of year.

Fig.5.13. 24hMicrophysical combination 30. Dec 2010 at 10.15 UTC

2. NOAA, AVHRR instrument

The cold water cloud can be seen in the infrared image combination
(3,7 µm + 10,9 µm + 12,0µm). The stratiform cloud is clearly seen between the high frontal clouds (whitish), but as the ice cloud over Eastern Finland appears pinkish, there might well be water clouds beneath it.

Fig. 5.14. 345-combination Dec 2010 at 10.10 UTC

The fine structure of the cloud can be seen in the very high resolution infrared image (12,0µm). The cloud layer is fairly uniform, but it is lightly broken here and there. 

Fig. 5.15. IR channel 12,0 µm 30th Dec 2010 at 10.10 UTC

 

Radar


The vertical cross section shows that there are intensive cells within the cloud layer:

Fig. 5.16.a. Cross section from the Kuopio radar 30. Dec 2010 at 13.15 UTC, with color scale

Fig. 5.16.b. Location of cross section

In the Vantaa radar CAPPI image there are intensive echoes among weaker ones:

Fig. 5.17. CAPPI image from the Vantaa radar 30. Dec.2010 at 12.00 UTC, with color scale.

In the hydrometeor classification radar product it can be seen that there is wet snow within the cloud, in the same locations as the strongest CAPPI echoes:

Fig. 5.18.a. HCLASS_PPI product from the Vantaa radar 10 Dec 2010 at 12.00 UTC, with color scale