He didn't talk much as they changed into their school robes, and was still glowering when the Hogwarts Express slowed down at last and finally stopped in the pitch-darkness of Hogsmeade station.
When Aunt Petunia put a quarter of unsweetened grapefruit onto Dudley's plate with a tremulous " There you are, Diddy darling, " Dudley glowered at her.
But before he could say anything else, the door flew open again as Harry had known it would, and there stood Hagrid, glowering down at him and looking, despite the flowery apron, positively alarming.
This basically means the same thing as " glower" , but there's a sense of some duration, so it means to look at somebody or something in an angry way continuously.
Every now and then Umbridge shot glowering looks at Harry, who kept his head down, staring at Defensive Magical Theory, his eyes unfocused, thinking . . .