I restricted the range of charts to 850mb equivalentpotentiela temperatur ("ThetaE") + surface pressure,
and 500mb temperatur + geopotential. Source : Wetter3
Wednesday, 17.January 2007 - 00 UTC
The upper level map shows a strong meandering upper flow over the North Atlantic Ocean spreading into Northern Europe, deflected by a longwave ridge over Eastern Europe to the North. Frontal system over the British Isles is clearly situated ahead of the trough axis, strengthening its weather activity significantly. It belongs to a North Atlantic low-pressure-system to the South of Greenland. Cold front passes into a wave as it can be seen by the recessed 1015mb-isobar. By the time, Central Europe is located in a weak southwestern flow. The waving cold front of the Finland low is trailing over the southerly North Sea up to the Baltic Sea.
The extended and rather energetic 985mb surface pressure low designated "Kyrill" marginally lies ahead of the trough axis under weak cyclonic vorticity advection leading to deepening surface pressure. Moreover, the low rapidly propagates southeastward due to its location nearby the axis of the intense jetstream. The low is already weakly occluded.
Wednesday, 17.January 2007 - 12 UTC
After 12 hours, the surface low deepened noticeably to 970mb and exhibits a coiling occlusion front right now.
At the triple point, the isolines of ThetaE are less densely packed than upstream along the cold front respectively warm front.
Additionally, the surface low (white circle) is situated rather far from te trough axis to the east of Newfoundland, and also pretty close to the upper level trough filled with deep cold air. From a quasi-geostrophic point of view, one can suppose that cyclogenesis peaks out soon on the basis of a such position.
The cold front of the Scotland low continues with strong rainfall, underlying a region with strong cyclonic vorticity adcection ahead of the trough axis. Now, southwestern flow gradually increases especially over Western Germany and Benelux. Broad area sees strong and stormy wind gusts during the afternoon hours, partly severe gales has been observed with the cold front passage.
Thursday, 18.January 2007 - 00 UTC
At night to Thursday, crucial development is realized at the triple point of the surface low "Kyrill":
Previously considered surface low Kyrill 1 continues its filling process and forms a separated upper level low core. As you can see by the 500mb chart, the surface low is situated in the rear of the trough axis at present. Upon that fact, one can conclude two consequences:
- 1. Surface low fills up.
- 2. Surface low remains stationary.
However, triple point clearly lies ahead of the trough axis and furthermore in the left exit region of the jetstream resulting into strong cyclonic vorticity advection respectively the strongest upward motions. Owing to its postion nearer to the jet axis, the "secondary low" formed at the triple point rapidly moves eastward. This secondary low, Kyrill 2, is the real low-pressure system Kyrill, that strucked Central Europe.
I will explain the factors of secondary cyclogenesis at the triplepoint more in detail in the second part of the analysis using the according satellite imagery.
Thursday, 18.January 2007 - 06 UTC
Six hours later, Kyrill arrived in Ireland. Core pressure is fallen from about 970mb at the triple point to 966mb. The occlusion front of the "old" Kyrill slowly detaches from the new occlusion front. As a result of the aforementioned anticyclonic vorticity advection, the core pressure of Kyrill 1 rised from 967mb up to 974mb. Formerly belonging upperlevel low moved eastward. Kyrill continues its position ahead of a distinctive trough axis with intense upward motion. Owing to the approaching intense low-pressure system, westsouthwesterly flow increases throughout the whole troposphere. Initially, maximum flow is accomplished in the warm sector over Southern England at that time. Kyrill overcame hurricane force in the flat country there, too.
Cold air masses embedded in the Po Valley and similaneously beginning warm air advection with strong pressure fall to the north of the Alps favours an initially deep, later shallow southern Foehn flow in the Wipp Valley. The consequences for Innsbruck have been discussed in a separated case study (in german).
Thursday, 18.January 2007 - 12 UTC
Another period of six hours, the intense low-pressure system already moved to the "Doggerbank" in the east of UK. Core pressure fell only a few mb. This is one of the special features of this storm sitation to be completely formed already far from the arrival in Central Europe.
In contrast, windstorm "Lothar" 1999 experienced its rapidly deepening no more than over Western Europe.
A strong air mass gradient forms along the cold front - additionally embedded into the strongest and deep flow and lying shortly head of the trough axis, as well as the surface low, while the jetstreak reaches about 100 Kts in 500mb. It couldn't have been better conditions for violent vertical transfers and convective severe storms. Isobars are densely packed in the warm sector yet. In the Ore Mountains and adjacent flat country of Saxony, hurricane force could be observed despite assumed stable warm air layer. Hydraulic effects in the lee of the mountain ridge mixed the extreme upper winds of 70-80 Kts in 850mb downward. Otherwise, most of the flat country in germany saw gale and severe gales, in extremely southwestern germany some gale-force wind gusts. Passing cold front appeared to be strongest over Benelux and Southern England. Amsterdam reported a wind gust of 130km/h at 12 UTC.
To the west of Ireland, the cold front trails with an elongated wave forming, showing somewhat tendency to a occlusion front (denoted). Upstream, the cold front continues to wave, but at first without significant lowering tendency.
Thursday, 18.January 2007 - 18 UTC
18 UTC... Kyrill peaks out over the western Baltic Sea. Cold front extended across Germany from the Northeast to the Southwest. Respective trough axis lies over Western Germany - hence the cold front see the strongest forcing. Most of its active part with thunderstorms and severe hurricane force winds is found over Northern and Eastern Germany, with upper cold pool above. By reason of this configuration, the cold front did not pass entire Germany, alternatively in extreme Southwestern Germany extreme hurricane-force winds held off. However, remarkable wind gusts have been observed at 18 UTC... 144km/h in Düsseldorf, 133km/h in Chemnitz as well as strong/violent tornado event in Wittenberg.
Elsewhere, broad area saw severe gales and gale-force wind gusts, partly hurricane force, especially in the northwestern part of the country where damage has been so hard that several rural districts called for red alert and several villages have been completely insulated. Partial blackouts with cold front passage in Eastern Germany took many hours, even long after the event.
A trough line producing again hurricane-force winds and intense (but not electrified) showers in the the rear of the cold front approaches. Developping wave to the southwest of Ireland weakens again,however, another wave follows upstream located in the range of strong air mass differences - additionally favoured to be placed ahead of a longwavy trough to the south of Newfoundland
Friday, 19.January 2007 - 00 UTC
The intense low-pressure system Kyrill is situated with nearly unchanged core pressure (lowest pressure 964,8mb) over the Bay of Danzig. Cold front propagates with gradually weakening further southeastward. Czech Republic and Eastern Austria see hurricane-force winds, too, indeed the thunderstorm activity degrades. However, the filling process of the surface low is rather slow. Reason for this can be found in the upperlevel charts where the surface core still lies ahead of the trough axis, albeit close to the upper core.
Flow turns to northwesterly directions backward of the trough. Embedded weak wave causes greater amounts of rain over southwestern and southern germany. Intense northwesterly upper flow with 60 Kts in 700mb results in a massive north foehn situation in Northern Italy where 850mb temperatures arise about 15°C. Upstream second wave development continues - later generating the low-pressure system "Lancelot" .
Freitag, 19.Januar 2007 - 06 UTC
Friday morning...Kyrill moves further to Western Russia. Most parts of Western and Central Europe experience a short calm weather period. Cold front clearly goes out of the range of the upper level trough, subsequent wave caps the convective activity. Air masses in the south of the Alps are much warmer than to the north in the warm sector of the wave, as a result of strong west and north foehn winds. Consequently, strong north foehn winds can be observed in Innsbruck - with maximum gusts of 101km/h nearby the airport Kranebitten.
Within the next days, Kyrill gradually moves to the Kara Sea in the north of Russia and fills up till death.
