British artillery observers looking down above the Aliakmon River on 14 April 1941 could see German vehicles moving south. The observers were about 2,000 feet above the river.
During 13 and 14 April, they had seen German fighters and dive bombers flying at low level and attacked the defensive positions in the pass. The only anti-aircraft guns were four Yugoslav Skoda guns and "four Greek guns". The Greek guns were positioned near the main road.
The New Zealand troops didn't like seeing the German dive bombers diving, dropping their bombs, and climbing back up. The dive bombers attacked the guns and also tried to crater the road.
They expected that the bombing attack was happening just before the Germans moving south from Kozani staged an attack. A feature of the bombing was that some of the dive bombers were fitted wth a noise-making device that was intended to disturb the men being bombed.
By 2pm on 14 April, the Germans had passed Petrana. That was about six miles south from the Aliakmon River.
By the time dark fell, the German guns started firing ranging shots. By about midnight, they started shelling the "ANZAC positions". By 8pm, they could see the headlights of German vehicles on the move. They were moving west into the hills in the direction of Grevena. This is based on the account in "Greece, Crete, and Syria" by Gavin Long.