Weather

The second half of September look set to be dominated by low pressure, with little chance of a prolonged dry settled spell of weather.

All computer weather models are indicating that temperatures are likely to be below normal, with rain expected at times across the UK - although there will be some dry, bright days especially in the south and east at first.

Heavy rain on wednesday led the River Aire to burst its banks into the flood plain near Skipton, shown in the picture below.



This highlights the fact that the water table remains high, following the wettest April on record, and the wettest summer in 100 years.

Since March, there hasn't been a prolonged spell of dry weather which would naturally allow the land to dry out and the water table to fall, and should the traditionally wet months of October and November materialise, then a renewed risk of flooding is a distinct possibility.

The floods of autumn 2000 were unprecedented in their scale and severity, and such was the volume of rainfall that fell, that it became the wettest autumn in the Central England data set which goes back to 1766.

But the flooding was made far worse because there were no spells of settled, dry weather in any of the previous months.

April 2000 was the wettest on record and June 2000 was also very wet, with the River Ouse rising to its highest ever June level, as parts of the region experienced flooding.

But crucially July and August 2000 - the warmest two months of the year, when evaporation rates are at their highest - whilst not classed as a washout, saw no period of prolonged dry weather over a period of weeks which would have allowed the land to dry out.

So in 2000, far less rainfall in October of that year would have caused some flooding, because the land was already so wet.

We can only hope that whilst the rest of September is likely to see more rainfall, the rest of autumn shows some improvement, or further flooding may become a reality.

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Comments

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  • Comment number 107. Posted by ukpahonta

    on 21 Sept 2012 22:32

    Time will tell.

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  • Comment number 106. Posted by greensand

    on 21 Sept 2012 21:34

    105. ukpahonta wrote:

    "All this is just speculation on my part and before anyone is prompted to request it being presented in a paper..."

    Ah, yes, some have never been able to differentiate between fact and speculation. A situation further confused by their constant attempt to dismiss or accept either solely upon the premise of who has made the statement.

    Interesting speculations ukp, a lot on sound ground, the rest we wait and see. Time will tell.

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  • Comment number 105. Posted by ukpahonta

    on 21 Sept 2012 20:58

    Greensand

    Thank you, some additional thoughts for a Friday evening.

    Of course the description also leads to the realisation, as mentioned previously that the current period may not lead to the El Nino required to boost atmospheric temperatures to the level required by the MO decadal forecast.

    More worrying though is if there is not enough energy being absorbed into the Pacific tropical ocean to replenish the warm pool, through increased cloud cover from external sources possibly, Svensmark, or lower than normal trade winds due to disturbance from the jet streams settling further from the poles possibly due to the quiet solar cycle, Scaife. Then a period less dominated by El Nino will see atmospheric temperatures affected less from the Pacific ocean and possibly other oceanic oscillations turning negative.
    Does this give some indication of how trivial changes in 'TSI' are not the overall influence of our major source of energy?

    All this is just speculation on my part and before anyone is prompted to request it being presented in a paper, sorry I have a day job, but others are getting there as I often point out.

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  • Comment number 104. Posted by greensand

    on 21 Sept 2012 20:06

    Link omitted from 103, apologies

    http://weather.unisys.com/surface/sst_anom.gif

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  • Comment number 103. Posted by greensand

    on 21 Sept 2012 20:03

    101.ukpahonta wrote:

    "A quick ENSO 101"

    ukp, to my understanding that is as good a consise ENSO 101 as there is. Very well put.

    Interestingly at present we have more of a cool pool North of Australia and a warm pool in the seas surrounding Japan. The Japan warm pool normally associated with La Nina conditions? I did have a ref but can't find it.

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  • Comment number 102. Posted by ukpahonta

    on 21 Sept 2012 19:54

    The localised effects of this process is apparent within North Australian and South Asian weather. La Nina provides monsoons and flooding, El Nino provides drought which is why the Australian government was so keen on building dams and maintaining sufficient water levels within them during the last 30 years.

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  • Comment number 101. Posted by ukpahonta

    on 21 Sept 2012 19:36

    A quick ENSO 101

    During La Nina the trade winds gather force and blow clouds to the West of the tropical Pacific ocean. This creates a large area of Pacific ocean without impedance to the Suns energy. The trade winds also move the oceans surface to the West which creates the warm pool to the North of Australia. As the ocean surface is forced into this area the heated surface water is forced down into the depths. According to the observation during this period the difference in ocean height between the West Pacific and the East can reach 0.5 metre. ENSO neutral has milder trade winds than La Nina but the end effect is the same.

    When the trade winds disperse then gravity takes over and the ocean height equalizes allowing the warm pool to the North of Australia to move Eastwards bringing the warm water out of the depths. This is El Nino, as the warm water moves to the East so does the enhanced evaporation and cloud cover thus restricting the warming of the ocean by the Sun but increasing the energy release to the atmosphere.

    This gives the process of the ocean absorbing energy from the Sun and then releasing it to the atmosphere. La Nina, and neutral conditions to a lesser extent, absorb energy into the ocean, El Nino releases energy into the atmosphere.

    Bob Tisdale has a much better explanation within his book and also looks at how the energy is spread from the Pacific tropical region.

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  • Comment number 100. Posted by QuaesoVeritas

    on 21 Sept 2012 18:47

    I have only read a part of the Tisdale blog (IMHO there is a lot of irrelevant stuff in the "OVERVIEW" section), but I am puzzled by the followong statements:
    "On the other hand, an El Niño takes naturally created warm water from below the surface of the western tropical Pacific and relocates it the surface."
    and
    "The next question you may have: The El Niño released lots of warm water from below the surface of the western tropical Pacific, but how was that warm water created?
    It was created during a La Niña that came before the El Niño. This happens because La Niña events reduce cloud cover and allow more sunlight than normal to penetrate and warm the tropical Pacific."
    So does that mean that the sunlight heats the ocean from below the surface, before it heats the surface?
    No doubt this will be explained later in the blog.

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  • Comment number 99. Posted by ukpahonta

    on 21 Sept 2012 18:39

    #98 Newdwr54

    It would be better if you relied upon your own intellect, not saying that you should agree with him or not, but if you want to understand what he says, then you should at least take the time to read what he says.

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  • Comment number 98. Posted by newdwr54

    on 21 Sept 2012 17:40

    97. ukpahonta wrote:

    "You are correct, you don't understand Tisdale's hypothesis, but his book would correct that for you, I'm sure that you may find a reference to it somewhere on his site!"
    _________________________________________________________

    I have to rely on a book, or else a blog comment, to decide whether a 'game-changing' hypothesis is right or not.

    As for peer review...?

    Can we not just forget about peer review, now that we have the likes of (Eng. Lit. grad) James Delingpole and (Former TV weatherman) Anthony Watts to keep us right?

    I mean, what would 'scientists' know that this pair wouldn't?

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