php - file_get_contents and div

What's wrong with my code?
I wish to get all dates from
but my array is empty.

$url = "http://weather.yahoo.com/";
$page_all = file_get_contents($url); 

preg_match_all('#
(.*)
#', $page_all, $div_array);


echo "
";
print_r($div_array);
echo "
";
?>

Thanks