Severe weather in North Italy and the Balkans
Valid: Tue 09 Jul 2019 06:00 to Wed 10 Jul 2019 06:00 UTC
Issued: Mon 08 Jul 2019 22:45
A level 2 was issued for N Italy, France (Corsica), Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Serbia and Bulgaria mainly for large or very large hail, severe convective wind gusts and tornadoes.
A level 1 was issued for NE Spain, S France, Italy, S Switzerland, S Austria, Croatia, Bosnia and Herzegovina, Montenegro, Serbia, North Macedonia, Bulgaria, N Albania and N Greece mainly for large hail, severe wind gusts and tornadoes.
A level 1 was issued for NE Turkey and Georgia mainly for large hail and severe wind gusts.
A level 1 was issued for parts of Russia for excessive precipitation and severe wind gusts.
A large synoptic vortex is found over the Baltic States and W Russia, and the jet stream in its southern flank over Central Europe is intensifying. The cut-off low over Spain is slowly moving east-northeast and it is weakening fast, but it has created a jet streak which will reach Italy on Tuesday 9 July 2019. Very moist air masses with steep mid-level lapse rates aloft are found in West and Central Mediterranean, as well as in the Balkans, where we expect numerous thunderstorms. Also, far Eastern Europe will experience some thunderstorms, locally producing severe weather.
N Italy, France(Corsica), Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Serbia and Bulgaria
Air masses with very high theta-e values can be found over and around Italy, and West Balkans. Several shortwave troughs will cross North Italy and Central Europe traveling east to the Balkans, providing lift to these unstable air masses. Low-level convergence zones in the Po Valley will trigger convection even before 12z and storms will quickly be able to become supercells. NWP models forecast a highly volatile environment with more than 2000 J/kg MLCAPE and 20-30 m/s DLS. High values of SREH0-3km (150-300 m2/s2) also support the development of supercells able to create very large hailstones and severe wind gusts. The storms should move over the Adriatic Sea during the night of Tuesday and early morning of Wednesday, but they will still pose a threat to the east coast of Italy.
Over the Balkans, the ongoing DMC in the North Adriatic Sea may produce locally severe weather especially in Croatia and Bosnia and Herzegovina by the morning hours of Tuesday. In the afternoon of Tuesday CAPE is forecast to range between 1000 - 1500 J/kg by both IFS and GFS, and DLS will locally reach 30 m/s. Strong 0-3km bulk shear and curved hodographs also suggest a high potential for supercells in the afternoon with an elevated threat for tornadoes. Storms will be able to travel long distances producing severe weather. During the night of Tuesday, the convection will be elevated but still large hail and severe wind gusts will be possible.
NE Spain, S France, Italy, S Switzerland, S Austria, Croatia, Bosnia and Herzegovina, Montenegro, Serbia, North Macedonia, Bulgaria, N Albania and N Greece
In NE Spain and South France, the remnants of the cut-off low will be still able to lift unstable air masses and even though the lapse rates are decreasing, large hail will be still possible given more than 1000 J/kg MLCAPE and 15-25 m/s DLS.
In Corsica a level 2 area was issued as storms will get the benefit of strong DLS and to organize in big clusters, with some of the storms becoming supercells creating large hail or very large hail and severe wind gusts.
For S Switzerland, S Austria, Central Italy and E Bulgaria, only a few storms will be able to produce severe weather and the main threat will be severe wind gusts given the high delta-theta-e values in NWP outputs.
Turkey, Georgia and Russia
An elongated cold front of the large vortex in Russia is extending from Russia towards N Turkey. On this boundary, plenty of moisture will feed storms that could get the benefit of locally enhanced DLS. Slow-moving storms, especially in Russia, will be able to produce excessive precipitation, while in Turkey and Georgia the main threat will be the severe wind gusts. Convection should be very limited during the night.
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Storm Miguel Batters Parts of Europe
In early June 2019, Storm Miguel brought high winds and heavy rain to a number of countries in Western Europe.
- Date & Time: 06 June 2019 00:00 UTC–8 June 12:00 UTC
- Satellites: Meteosat-10 and 11
- Instruments: SEVIRI
- Channels/Products: Airmass RGB, High Resolution Visible, IR10.8 Rapid Scan
On 5 June, AEMET, the Spanish Meteorological Agency, named a rapidly developing low-pressure system as Storm Miguel, it was the 23rd named storm of the 2018/19 European windstorm season. Part of north-west Spain and Portugal were battered by heavy rain, high winds and large waves. Winds of up to 147km/h hit northern Spain, then the storm swirled around the Bay of Biscay, before moving on to France.
On 7 June Storm Miguel produced gusts up to 80 mph (129 km/h) along the Atlantic coast of France. At Île d'Yeu, France, one of these gusts set a record for the month of June, last set in 1981.
By 8 June the tail end of the storm had hit parts of the UK (with gusts up to 65 km/h and heavy rain), the Netherlands and even as far north as Finland.
This extratropical cyclone developed in a rapid cyclogenesis process, where the initial disturbance on the polar front produces very quick formation of a deep low-pressure centre.
Meteosat-10 Airmass RGB with MSLP overlaid (Figure 1)
6 June 00:00–21:00 UTC, EUMETSAT
One of the criteria defining rapid cyclogenesis is that the pressure drop is more than 1 hPa an hour. The MSLP (Mean Sea Level Pressure) values in Figure 1, show pressure drops of more than 16 hPa in 12 hours, during the transition from the development to the advanced stage of this cyclone.
Rapid cyclogenesis normally happens at the left exit region of the upper-level jet stream (Figure 2) and it goes through three major stages:
- Development of a ‘cloud head’, sitting on the cold side of the main cloud band — the result of a cold conveyor belt split, creating typical convex-shaped cloud edge.
Strong dry intrusion in the region between the cloud head and cloud band — the result of subsidence of stratospheric air, leading to more positive vorticity and deepening of the cyclone.
- Deepening of the low pressure centre and wrapping of the cloud bands around it (advanced stage).
- These stages are well seen through animated Airmass RGB imagery (Figure 3), since this RGB product nicely shows warm and moist air masses in green shades, cold ones in blue shades, and stratospheric intrusion (e.g. tropopause folding) in red stripes.
Meteosat-11 Airmass RGB (Figure 3)
5 June 12:00 UTC–8 June 12:00 UTC, EUMETSAT
In the advanced, mature stage, when the cloud spiral is well developed and circling the cyclone's centre, parallel cloud lines can appear close to the innermost part of the cloud spiral. These cloud bands are parallel rain bands.
Although rain bands are, by their nature, more visible on radar than in satellite images, five minute rapid scanning imagery, capable of showing some cloud properties connected to rainfall rates, serve as a valid proxy.
Rapid scanning does not provide a lot of additional value for analysis of systems of that size, however, more images in a certain time period can aid in the nowcasting of individual convective cells embedded in associated cloud bands.
A good proxy for rain rates is normally the IR10.8 SEVIRI channel, which informs on the height of the thick cloud, hence its ability to produce more, or less, rain (see animation in Figure 4).
Meteosat-11 IR10.8 RSS (Figure 4)
6 June 12:00 UTC–7 June 12:00 UTC, EUMETSAT
Cyclones such as Miguel are normally associated with strong rain and wind episodes, so this cyclone was not exceptional, nor was it classified as major. However, it was unusual because it developed during a warm season, such cyclones usually form in the winter months. Also, this storm is a noteworthy example of the rapid cyclogenesis process.
- Three dead after a rescue lifeboat overturned off the French coast.
- French fishing boat missing, with crew assumed dead.
- 28,000 homes in the west of France left without electricity.
- In Jersey several trees were blown down.
- An Irish yacht crew, sailing off the Spanish coast, had to be rescued by helicopter.
Wind field at 850 hPa pressure level, overlaid over HRVIS image, reveals the intense wind episodes on the west coast of France (Figure 5).
This article was adapted from the EUMETSAT website published by Ivan Smiljanic (SCISYS) and Sancha Lancaster (Pactum).
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