New Delhi:  Delhi since early morning today has been engulfed in a thick blanket of fog accompanied by a noticeable drop in temperature. The low visibility has slowed down traffic on roads. At least 20 flights - 11 international and 9 domestic - in and out of the Delhi international airport have been delayed. At least one train has been cancelled, 9 rescheduled and 25 trains arriving in Delhi are delayed. The weather department predicted smog,cold winds and likely rainfall.