<div class="eI0">
  <div class="eI1">Mod&egrave;le:</div>
  <div class="eI2"><h2><a href="http://en.wikipedia.org/wiki/European_Centre_for_Medium-Range_Weather_Forecasts" target="_blank">ECMWF</a>: Global weather forecast model from the "European Centre for Medium-Range Weather Forecasts". ECMWF is now running its own Artificial Intelligence/Integrated Forecasting System (AIFS) as part of its experiment suite. These machine-learning-based models are very fast, and they produce a 10-day forecast with 6-hourly time steps in approximately one minute. </h2></div>
 </div>
 <div class="eI0">
  <div class="eI1">Mise &agrave; jour:</div>
  <div class="eI2">4 times per day, from 3:30, 09:30, 15:30 and 21:30 UTC</div>
 </div>
 <div class="eI0">
  <div class="eI1">Greenwich Mean Time:</div>
  <div class="eI2">12:00 UTC = 14:00 CEST</div>
 </div>
 <div class="eI0">
  <div class="eI1">R&eacute;solution:</div>
  <div class="eI2">0.25&deg; x 0.25&deg;</div>
 </div>
 <div class="eI0">
  <div class="eI1">Param&egrave;tre:</div>
  <div class="eI2">Maximum wind velocity of convective wind gusts</div>
 </div>
 <div class="eI0">
  <div class="eI1">Description:</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">NWP:</div>
  <div class="eI2">La pr&eacute;vision num&eacute;rique du temps (PNT) est une application de la m&eacute;t&eacute;orologie et de l'informatique. Elle repose sur le choix d'&eacute;quations math&eacute;matiques offrant une proche approximation du comportement de l'atmosph&egrave;re r&eacute;elle. Ces &eacute;quations sont ensuite r&eacute;solues, &agrave; l'aide d'un ordinateur, pour obtenir une simulation acc&eacute;l&eacute;r&eacute;e des &eacute;tats futurs de l'atmosph&egrave;re. Le logiciel mettant en &oelig;uvre cette simulation est appel&eacute; un mod&egrave;le de pr&eacute;vision num&eacute;rique du temps.<br><br>
<br>Pr&eacute;vision num&eacute;rique du temps. (2009, d&eacute;cembre 12). Wikip&eacute;dia, l'encyclop&eacute;die libre. Page consult&eacute;e le 20:48, f&eacute;vrier 9, 2010 &agrave; partir de <a href="http://fr.wikipedia.org/w/index.php?title=Pr%C3%A9vision_num%C3%A9rique_du_temps&oldid=47652746" target="_blank">http://fr.wikipedia.org/w/index.php?title=Pr%C3%A9vision_num%C3%A9rique_du_temps&oldid=47652746</a>.<br>
</div></div>
</div>