<div class="eI0">
  <div class="eI1">Modelo:</div>
  <div class="eI2"><h2>CFS: The NCEP Climate Forecast System (CFS)</h2></div>
 </div>
 <div class="eI0">
  <div class="eI1">Actualiza&ccedil;&atilde;o:</div>
  <div class="eI2">1 times per day, at 17:00 UTC</div>
 </div>
 <div class="eI0">
  <div class="eI1">Greenwich Mean Time:</div>
  <div class="eI2">12:00 UTC = 12:00 WET</div>
 </div>
 <div class="eI0">
  <div class="eI1">Resolution:</div>
  <div class="eI2">1.0&deg; x 1.0&deg;</div>
 </div>
 <div class="eI0">
  <div class="eI1">par&acirc;metro:</div>
  <div class="eI2">Maximum wind velocity of convective wind gusts</div>
 </div>
 <div class="eI0">
  <div class="eI1">Descri&ccedil;&atilde;o:</div>
  <div class="eI2">

The method of Ivens (1987) is used by the forecasters at KNMI to predict the
maximum wind velocity associated with heavy showers or thunderstorms. The
method of Ivens is based on two multiple regression equations that were
derived using about 120 summertime cases (April to September) between 1980 and 1983.
The upper-air data were derived from the soundings at De Bilt, and
observations of
thunder by synop stations were used as an indicator of the presence of
convection.
The regression equations for the maximum wind velocity (w<sub>max</sub> ) in m/s
according
to Ivens (1987) are:<br>
<ul type="square">
<li>if T<sub>x</sub> - &#952;<sub>w850</sub> &lt; 9&deg;C
<dl>
<dd>w<sub>max</sub> = 7.66 + 0.653&sdot;(&#952;<sub>w850</sub> - &#952;<sub>w500</sub> ) + 0.976&sdot;U<sub>850</sub><br></dd>
</dl>
<li>if T<sub>x</sub> - &#952;<sub>w850</sub> &ge; 9&deg; C</li>
<dl>
<dd>w<sub>max</sub> = 8.17 + 0.473&sdot;(&#952;<sub>w850</sub> - &#952;<sub>w500</sub> ) + (0.174&sdot;U<sub>850</sub> + 0.057&sdot;U<sub>250</sub>)&sdot;&radic;(T<sub>x</sub> - &#952;<sub>w850</sub>)<br></dd>
</dl>
</ul>
<br>
where 
<ul>
<li>T<sub>x</sub> is the maximum day-time temperature at 2 m in K
<li>&#952;<sub>wxxx</sub> the potential wet-bulb temperature at xxx hPa in K
<li>U<sub>xxx</sub> the wind velocity at xxx hPa in m/s.
</ul>
The amount of negative buoyancy, which is estimated in these
equations
by the difference of the potential wet-bulb temperature at 850 and at 500 hPa,
and horizontal wind velocities at one or two fixed altitudes are used to estimate
the maximum wind velocity. The effect of precipitation loading is not taken into
account by the method of Ivens.
(Source: <a href="http://www.knmi.nl/" target="_blank">KNMI</a>)

    
  </div>
 </div>
 <div class="eI0">
  <div class="eI1">CFS:</div>
  <div class="eI2">The CFS model is different to any other operational weather forecasting model you will see on Weatheronline.
<br>
Developed at the Environmental Modelling Center at NCEP (National Centers for Environment Prediction) in the USA, 
the CFS became operational in August 2004.
<br>
The systems works by taking reanalysis data (NCEP Reanalysis 2) and ocean conditions from GODAS 
(Global Ocean data Assimilation).  Both of these data sets are for the previous day, and so you 
should be aware that before initialisation the data is already one day old.
<br>
Four runs of the model are then made, each with slightly differing starting conditions, and from 
these a prediction is made.
<br>
Caution should be employed when using the forecasts made by the CFS. However, it is useful when 
monitored daily in assessing forecasts for the coming months, the confidence levels in these 
forecasts and in an assessment of how such long range models perform.
<br>
A description of the CFS is given in the following manuscript.<br>
S. Saha, S. Nadiga, C. Thiaw, J. Wang, W. Wang, Q. Zhang, H. M. van den Dool, H.-L. Pan, S. Moorthi, D. Behringer, D. Stokes, M. Pena, S. Lord, G. White, W. Ebisuzaki, P. Peng, P. Xie , 2006 : The NCEP Climate Forecast System. Journal of Climate, Vol. 19, No. 15, pages 3483.3517.<br>
<a href="http://cfs.ncep.noaa.gov/" target="_blank">http://cfs.ncep.noaa.gov/</a><br>
</div></div>
 <div class="eI0">
  <div class="eI1">NWP:</div>
  <div class="eI2">A previs&atilde;o num&eacute;rica do tempo usa o estado instant&acirc;neo da atmosfera como dados de entrada para modelos matem&aacute;ticos da atmosfera, com vista &agrave; previs&atilde;o do estado do tempo.<br>
Apesar dos primeiros esforços para conseguir prever o tempo tivessem sido dados na d&eacute;cada de 1920, foi apenas com o advento da era dos computadores que foi possível realiz&aacute;-lo em tempo real. A manipulaç&atilde;o de grandes conjuntos de dados e a realizaç&atilde;o de c&aacute;lculos complexos para o conseguir com uma resoluç&atilde;o suficientemente elevada para produzir resultados úteis requer o uso dos supercomputadores mais potentes do mundo. Um conjunto de modelos de previs&atilde;o, quer &agrave; escala global quer &agrave; escala regional, s&atilde;o executados para criar previsões do tempo nacionais. O uso de previsões com modelos semelhantes ("model ensembles") ajuda a definir a incerteza da previs&atilde;o e estender a previs&atilde;o do tempo bastante mais no futuro, o que n&atilde;o seria possível conseguir de outro modo.<br>
<br>Contribuidores da Wikip&eacute;dia, "Previs&atilde;o num&eacute;rica do tempo," Wikip&eacute;dia, a enciclop&eacute;dia livre, <a href="http://pt.wikipedia.org/w/index.php?title=Previs%C3%A3o_num%C3%A9rica_do_tempo&amp;oldid=17351675" target="_blank">http://pt.wikipedia.org/w/index.php?title=Previs%C3%A3o_num%C3%A9rica_do_tempo&oldid=17351675</a> (accessed fevereiro 9, 2010). <br>
</div></div>
</div>