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morfius

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    28 April London Area Storm Cells

    in Archived weather photography area

    Posted

    A few pictures I took of some rather decent storm cells that passed to my east on Tuesday:

    aaf71f.jpg

    2lvck86.jpg

    Rapid convection of cumulus clouds forming tall vertical columns.

    2dukz2d.jpg

    A really well formed cell complete with flat top and outstretched anvil:

    34pxfeu.jpg

    wuhy6b.jpg

    Half an hour after taking these, there were around ten of the above type within around 30 miles.

    Another half hour after that, most of them had dissipated!

    April 2009 Rainfall Stats

    in Weather reports

    Posted

    I don't work for TW anymore but the principle has not changed in the last 100 yrs so I doubt it has much in the last 4. 96% res storage is only @190,000 Ml (million litres). London Uses @2000 Ml of that water per day every day in theory a 95 day store, however the law of hydraulics means that these are only efficient at above 50% as they are on a gravity system and below that flow reduces as does quality (which reduces treatability) with depth. What this means is that in reality London has @50 days of reserves if river abstraction drops to zero, nowhere near enough to sustain a long summer period. The key figure is that of the remaining flow over Teddington weir the last weir in the Thames if this drops to zero the upper tidal reaches will become stagnant and there are legal requirements on TW to maintain a min flow. What is left in the river after that min flow can be abstracted but in the summer when there is little rain it is only sustained by ground water being released and if the previous winter was poor for that then TW will know early if it needs to impose any restrictions.

    To give you an example the min flow over Teddington can drop to 200Ml/d in the summer TW need to abstract 1000-1500 Ml/d to get through until October, so it is not easy or as straight forward as some would suggest. TW need to sustain 95% storage until the end of July to be entirely safe for the period

    Thanks for that, I didn't realise quite how complex the water management was.

    April 2009 Rainfall Stats

    in Weather reports

    Posted

    I would prefer to have a wet summer if it means avoiding water shortages.

    Thames water seem to have the definition of a water shortage as reservoirs at 96% capacity.

    Well at least they did in 2006 when they seemed to think that this level necessitated a hose ban....

    Today's Weather And General Chat

    in Weather reports

    Posted

    Has anyone seen the latest metoffice satellite imagery?

    There's a very interesting linear cloud feature extending from the Faroe islands and arcing down the north sea to north west France.

    Any explanations for this? perhaps the convergence of two air masses or something?

    Today's Weather And General Chat

    in Weather reports

    Posted

    It does occur, it happened this year, in winter at some point, the temp in mid winter got up to 15.c when the Foehn effect occured, BBC weather were talking about, its on there website how it particulalry affects eastern scotland and Leeds

    Also I seem to remember it getting up to 19C in the Scottish Highlands in February I think due to the Foehn.

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