Does terrain affect tornado genesis?

[Nigel Bolton]

Oooh and Mungo again does not believe that there are supercells and true tornadoes in Britain.

There ARE both true tornadoes and supercells in the UK.

Tornadoes are relatively common, though 95% of them are weak, doing no more damage than removing tiles from roofs and uprooting trees. Much stronger tornadoes do occur rarely, and cause considerable damage. Let's not forget that the UK is a naturally windy nation and buildings have been constructed to withstand very strong winds, so a tornado that removes all roofs and upper floors from an entire street of houses must be intrinsically strong.

I have personally seen tornado damage five or six times, and I have been amazed by what the tornado has done. Only one of the tornadoes caused injury, when a mobile home was overturned several times by the tornado, this rates as mid EF1 or T2.

As stated before, most UK tornadoes do not conform to the American model and are cool weather phenomena.

True supercells, however, are very rare in the UK, but are more common over Continental Europe. I have probably only ever witnessed one or two of these phenomena in my lifetime. By far the worst was the storm of 24/06/94 which arrived with a wall of lightning; whilst overhead, gave sustained winds of 30kt plus with gusts 50-60kt and up to 50mm of rain in 20 minutes. There was plenty of tree damage by wind and much lightning damage to property. This storm also produced a widespread asthma attack.

During the storm, the lightning was so frequent, raindrops were held in suspended animation by strobing.

It was estimated that this storm, and another further west gave up to 100,000 lightning discharges across the UK that evening.

I do not expect to see another storm like that in my lifetime.

N.

 

[Jody Radzik]

Oooh and Mungo again does not believe that there are supercells and true tornadoes in Britain.

To quote Nigel in the second post of the thread:

"These storms can ingest a vortex, and stretch it to produce a tornado."

Making this particular instance of a tornado either a landspout or a waterspout, depending on where the vortex was picked up. I suggested perhaps they were islandspouts, considering the fact they occur around the Isle of Wright.

Whatever you want to call them, they are not true supercell tornadoes, although I'm not saying that such is not possible in the U.K.

 

[Martin North]

I don't think he ever sugggested they were supercellular tornadoes. They are tornadoes though...all the same.

The English Channel is a hot-spot for Waterspouts to be fair. Jersey and Guernsey see loads. It holds it's temperature well into the winter...resulting in strong convection especially in November, December.

As far as European Supercells are concerned...the place to go is Poland & the Czech Republic. They get quite a lot in late Spring into Summer with various feeds of converging airmasses they have there.

 

[Tomas Pucik]

I can support this, eastern Germany, Poland and western Czech Republic do get the action from time to time. My friend living in Czech Republic had 3 supercells!! passing in 20 km range from him and he did not have to chase at all. This happened on 14th May this year. Two of them were LP in nature, other was Classic supercell. All of them caused significant hail damage . On 21st June another supercell produced 4 cm hail and passed just overhead of his observation site ( again, no chasing done) On same day, line of storms evolved into MCC and bow echo did travel across Slovakia, Hungary and southern Poland. Tree and roof damage with power outages were widespread. So yes, interesting things can happen here.
However, most of the tornadoes in Middle Europe are landspout in nature, for example, study for Czech republic has shown, that only fraction of tornadoes come from supercells. Many of tornadoes do occur in insignificant CAPE situations ( cold core setups with strong W/NW flow aloft), but some of tornadoes were up to F2, so there is no need to underestimate such setups.

 

[Nigel Bolton]

I can support this, eastern Germany, Poland and western Czech Republic do get the action from time to time. My friend living in Czech Republic had 3 supercells!! passing in 20 km range from him and he did not have to chase at all. This happened on 14th May this year. Two of them were LP in nature, other was Classic supercell. All of them caused significant hail damage . On 21st June another supercell produced 4 cm hail and passed just overhead of his observation site ( again, no chasing done) On same day, line of storms evolved into MCC and bow echo did travel across Slovakia, Hungary and southern Poland. Tree and roof damage with power outages were widespread. So yes, interesting things can happen here.
However, most of the tornadoes in Middle Europe are landspout in nature, for example, study for Czech republic has shown, that only fraction of tornadoes come from supercells. Many of tornadoes do occur in insignificant CAPE situations ( cold core setups with strong W/NW flow aloft), but some of tornadoes were up to F2, so there is no need to underestimate such setups.

Interestingly, I was in southern Poland on 21st June and the storms on this day were the best I saw anywhere during 2007. I was in the city of Gliwice, west of Katowice. However, none of the storms I witnessed that day were supercellular, but did contain some amazing lightning.

The first wave of storms moved through during the afternoon. All lightning was CG and each lightning strike maintained its channel open for several seconds, something I have rarely seen. There was little rain, and the wind throughout the storm remained light SEl'y.

The second wave of storms moved through during the evening and gave several hours of moderate rain. This storm gave infrequent, but remarkable lightning with many channels open at each strike, but each strike was several minutes apart. The only time the rain became heavy and there were some gusty winds was when the wind shifted from SE to NW. Durning this time the cloud base was lower, and stratus could be seen rapidly rising into the base. It was during this storm that the block of flats I was staying in was struck. I will try and find, if possible a link to the pictures of this particular strike and one other that was captures across the sky of Gliwice that night.

N.

 

[Nigel Bolton]

To quote Nigel in the second post of the thread:

"These storms can ingest a vortex, and stretch it to produce a tornado."

Making this particular instance of a tornado either a landspout or a waterspout, depending on where the vortex was picked up. I suggested perhaps they were islandspouts, considering the fact they occur around the Isle of Wright.

Whatever you want to call them, they are not true supercell tornadoes, although I'm not saying that such is not possible in the U.K.

The 800 metre wide EF2 tornado that swept across Selsey at 23:45 on 7th January 1998 did accompany a cell that arguably contained supercellular charactorisics, and interestingly is I believe one of the very few tornadic storms in the UK to generate large hail (25mm).

The storm formed in a cold weather situation where cold air from Canada was advected across the relatively warm waters of the Atlantic, the air becoming very unstable.

During the evening, strong westerly gradients were evident across the English Channel, whilst weaker gradients existed across southern England. This allowed the flow across southern England to decouple and generate an offshore northwesterly flow of just 5kt. A WSW'ly flow of 35 knots continued across the Channel. This separation of air generated a 'coastal front', a line of intense low level shear.

Strong thunderstorms ran along this zone of shear, the updraft forced by the shear, its positioning meaning the southern end of the updraft was propelled east at 35 knots plus, whilst its northern side was making 5 knots or so. This was allowing the cells to spin. Heavy rain and or hail fell out to the north of the zone of shear, and upper level winds, SW'ly indirection and of 50kt plus allowed the storm to vent efficiently to the northeast through the anvil.

One of these storms was able to ingest a vortex, and because it was already rotating, was then able to develop a large a strong tornado that then damaged over 1000 properties, some of them severely.

True, it was a waterspout over the oggin, but once it made landfall, it was a tornado,

N.

 

[MJ Poore]

As far as European Supercells are concerned...the place to go is Poland & the Czech Republic. They get quite a lot in late Spring into Summer with various feeds of converging airmasses they have there.

I have been told the Hungarian Plain is good in May? And parts of Romania along the Black Sea, they even have a US WSR 88 doppler network you can access online.

I have been searching for damage reports from these areas. But I havnt found anything yet, though.

 

[Paul Knightley]

Once again this thread highlights the problems in trying to ascertain how tornadoes actually develop. For example, there is no such thing as an, "Amercian model" of tornadogenesis. True, a number of tornadoes in the USA develop beneath mesocyclones/supercells but then again a large numbder develop beneath non-mesocyclone storms. Tornadoes develop because of features on the microscale, and perhaps meso-gamma scale, e.g. eddies on gust fronts.

I have a problem with terrain-induced tornadogenesis - I am certainly open to the idea, as certain locations (such as east of the IoW, as Nigel has suggested) seem prone to tornadoes compared with nearby areas. However, detailed modelling to see whether this is actually possible would certainly help. Eddies from topography could be ingested by a storm, but they would have to be of the correct approximate dimensions, to allow the storm time to spin them up into tornadoes.

So the answer to this thread should be, "possibly", but further scientific research is required. As we don't yet know exactly how tornadogenesis occurs, I'm not sure we can be certain that topography can influence it in a positive fashion.

And yes, of course supercells occur in the UK, as do tornadoes. Pay no attention to Mungo spouting off again! (or should that be sprouting off, as it's nearly Xmas!).