voila mon code
<?php
$dom = new DomDocument;
$dom->load("http://api.openweathermap.org/data/2.5/forecast/daily?q=Casablanca&mode=xml&units=metric&cnt=3");
$listePays = $dom->getElementsByTagName('max');
foreach($listePays as $max)
echo $temperature -> max->firstChild->nodeValue . "<br />";
$listePays = $dom->getElementsByTagName('min');
foreach($listePays as $min)
echo $temperature->min->firstChild->nodeValue . "<br />";
?>