Exodus 14:19

14:19 The angel of God, who was going before the camp of Israel, moved and went behind them, and the pillar 1  of cloud moved from before them and stood behind them.

Exodus 33:10

33:10 When all the people would see the pillar of cloud standing at the entrance of the tent, all the people, each one at the entrance of his own tent, would rise and worship. 2 

1 sn B. Jacob (Exodus, 400-401) makes a good case that there may have been only one pillar, one cloud; it would have been a dark cloud behind it, but in front of it, shining the way, a pillar of fire. He compares the manifestation on Sinai, when the mountain was on fire but veiled by a dark cloud (Deut 4:11; 5:22). See also Exod 13:21; Num 14:14; Deut 1:33; Neh 9:12, 19; Josh 24:7; Pss 78:14; 105:39.

2 tn All the main verbs in this verse are perfect tenses continuing the customary sequence (see GKC 337 §112.kk). The idea is that the people would get up (rise) when the cloud was there and then worship, meaning in part bow down. When the cloud was not there, there was access to seek God.