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Dreamin/ of a White Christmas?
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Lexilogio
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Joined: 25 Aug 2008
Posts: 7585


Location: North of the Watford Gap

PostPosted: Tue Nov 15, 2011 11:48 pm    Post subject: Re: Dreamin/ of a White Christmas?  Reply with quote

Rob wrote:
Lexilogio wrote:
Rob wrote:
Lexilogio wrote:
Are you dreaming of a white Christmas?

Find our your chances
 Find our your chances?


Typo. Have you tried the link?
 No, why would I?


Because you can see what percentage of chance there is for snow at Christmas where you are.

I have a 30% chance. Which I've had for the last 3 years. I did get some last year....
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genghiscant
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Joined: 29 Jun 2011
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PostPosted: Wed Nov 16, 2011 6:20 pm    Post subject: Reply with quote

Nobody can predict the weather with any accuracy more than five days ahead. Any further than that & it's a pure guess, there are just too many variables.
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Lexilogio
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PostPosted: Wed Nov 16, 2011 7:35 pm    Post subject: Reply with quote

genghiscant wrote:
Nobody can predict the weather with any accuracy more than five days ahead. Any further than that & it's a pure guess, there are just too many variables.


Well, not a pure guess... There are statistical probabilities depending on certain variables. But it can't be predicted with certainty.
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genghiscant
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PostPosted: Sat Nov 19, 2011 8:50 pm    Post subject: Reply with quote

Quote:
genghiscant wrote:
Nobody can predict the weather with any accuracy more than five days ahead. Any further than that & it's a pure guess, there are just too many variables.



Quote:
Well, not a pure guess... There are statistical probabilities depending on certain variables. But it can't be predicted with certainty.


Statistics will only give you trends. Predictions for this winter are impossible. For example, the severe winter for the south last year was at complete variance with the preceding 15 years & came as a bolt out of the blue. Nobody predicted it. If the trend of the last 16 years holds good, then it should be another mild winter in the south. But you just never know, it's impossible to tell.
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genghiscant
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PostPosted: Sat Nov 19, 2011 9:01 pm    Post subject: Reply with quote

Quote:
Numerical weather prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic results. A number of global and regional forecast models are run in different countries worldwide, using current weather observations relayed from radiosondes or weather satellites as inputs to the models.

Mathematical models based on the same physical principles can be used to generate either short-term weather forecasts or longer-term climate predictions; the latter are widely applied for understanding and projecting climate change. The improvements made to regional models have allowed for significant improvements in tropical cyclone track and air quality forecasts; however, atmospheric models perform poorly at handling processes that occur in a relatively constricted area, such as wildfires.

Manipulating the vast datasets and performing the complex calculations necessary to modern numerical weather prediction requires some of the most powerful supercomputers in the world. Even with the increasing power of supercomputers, the forecast skill of numerical weather models extends to about only six days. Factors affecting the accuracy of numerical predictions include the density and quality of observations used as input to the forecasts, along with deficiencies in the numerical models themselves. Although post-processing techniques such as model output statistics (MOS) have been developed to improve the handling of errors in numerical predictions, a more fundamental problem lies in the chaotic nature of the partial differential equations used to simulate the atmosphere. It is impossible to solve these equations exactly, and small errors grow with time (doubling about every five days). In addition, the partial differential equations used in the model need to be supplemented with parameterizations for solar radiation, moist processes (clouds and precipitation), heat exchange, soil, vegetation, surface water, and the effects of terrain. In an effort to quantify the large amount of inherent uncertainty remaining in numerical predictions, ensemble forecasts have been used since the 1990s to help gauge the confidence in the forecast, and to obtain useful results farther into the future than otherwise possible. This approach analyzes multiple forecasts created with an individual forecast model or multiple models.



http://en.wikipedia.org/wiki/Numerical_weather_prediction
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Lexilogio
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Joined: 25 Aug 2008
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Location: North of the Watford Gap

PostPosted: Sat Nov 19, 2011 11:02 pm    Post subject: Reply with quote

genghiscant wrote:
Quote:
genghiscant wrote:
Nobody can predict the weather with any accuracy more than five days ahead. Any further than that & it's a pure guess, there are just too many variables.



Quote:
Well, not a pure guess... There are statistical probabilities depending on certain variables. But it can't be predicted with certainty.


Statistics will only give you trends. Predictions for this winter are impossible. For example, the severe winter for the south last year was at complete variance with the preceding 15 years & came as a bolt out of the blue. Nobody predicted it. If the trend of the last 16 years holds good, then it should be another mild winter in the south. But you just never know, it's impossible to tell.






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