$days = array(
'Monday' => 'Среда',
'Tuesday' => 'Вторник',
//all days
);
foreach ($obj['forecast']['simpleforecast']['forecastday'] as $arr) {
$html .= "<td align='center'>" . strtr($arr['date']['weekday'], $days) . "<br />";
$html .= "<img src='http://icons-pe.wxug.com/i/c/k/" . $arr['icon'] . ".gif' border=0 /><br />";
$html .= "<font color='red'>" . $arr['high']['celsius'] . '°C' . " </font>";
$html .= "<font color='blue'>" . $arr['low']['celsius'] . '°C' . "</font>";
$html .= "</td>";
}
в нативном есть appendChild и insertBefore