Triple views of thunderstorms in Finland

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Thunderstorms across eastern and Northern Finland on 8 June 2019 could be easily tracked using all three Metop satellites that are now in orbit.

Date & Time
08 June 2019 00:00–23:45 UTC
Metop-A, B & C, Meteosat-11
Brightness Temperature, Infrared Channel

By Sreerekha Thonipparambil (EUMETSAT), Janne Kotro (FMI) and Ivan Smiljanic (SCISYS)

Metop-C, the third polar orbiting satellite, was launched on 7 November, 2018, and when it became fully operational on 3 July, 2019 it meant there were three Metop satellites on a Tristar constellation. This case study examines the benefit of having three Metop satellites when nowcasting for Nordic latitudes.

On Saturday, 8 June, Finnish Meteorological Institute (FMI) reported thunderstorms across eastern and northern Finland, with numerous lightning strikes (Figure 1). This band of thunderstorms resulted in thousands of power outages.

Figure 1
Figure 1: Lightning map (located ground flashes), 8 June 00:00–23:55 UTC (heikko = weak, kohtalainen = moderate, kova = strong, raju = severe). Credit: FMI

Geopotential height of the 300 hPa pressure level (thick red isolines, Figure 2) reveals the broad ridge over Eastern Europe and Scandinavia, where the jet stream roughly followed geopotential isolines on the northern edge of the high pressure region.

Figure 2
Figure 2: Met-11 IR10.8 image with overlay of Geopotential Height at 300 hPa and CAPE field 15:00 UTC

Finland was under a lower gradient field, with enhanced CAPE values (thin red and yellow isolines), plus a vertical wind shear was present due to the proximity of the jet streak. Under such synoptic conditions, and presence of the diurnal heating, more severe convective episodes can be expected.

Figure 3: Metop-A/B & C, AVHRR Brightness Temperature animation (zoomed in), 8 June 16:35–19:55 UTC

The evolution of this particular thunderstorm cell, located at northern Finland, could be followed on Metop AVHRR Brightness Temperature imagery (Figure 3), from 16:35 to 20:00 UTC. While in at 16:25 UTC there is only a small indication of the possibility of a convection initiation, after about 30 minutes, at around 17:16 UTC, the Metop-C overpass indicates the development of multiple convective cells in the area of interest, which is confirmed by the passage of Metop-B at around 17:49 UTC.

Figure 4
Figure 4: AVHRR Brightness Temperature from Metop-A at 16:35 UTC (left), Metop-C at 17:16 (middle) and Metop-B at 17:49 UTC (right)

From a nowcasting point of view, it is significant to note that between the image at 16:35 from Metop-A (Figure 4, left), where there is only a vague signal in the brightness temperature of a thunderstorm cell forming, and the image at 17:49 from Metop-B (Figure 4, right), where there is a pronounced thunderstorm cells, there is the Metop-C image at 17:16 (Figure 4, middle) which gives a strong indication of convective initiation. This would give local forecaster a lead time close to 30 minutes to issue warnings on the thunderstorm.

The thunderstorm could also be seen on the Metosat-11 infrared images (Figure 5). There is a mismatch on the exact location of the storm between the radar, SEVIRI and Metop imagery due to a parallax shift.

Figure 5: Meteosat-11 infrared animation, 8 June 00:00–23:45 UTC
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