11. As the floes stack up there, they create pressure ridges up to 40 feet high. 12. On February 27, Cyclone Percy encountered a high pressure ridge which slowed its forward speed. 13. This massive but gradual collision of ice against ice creates pressure ridges in the glacier. 14. The ice sheets can crunch into each other, layering to form pressure ridges 50-feet thick. 15. By then they were just north of pressure ridges . 16. High-pressure ridges , low-pressure troughs and the jet stream crowd the weather map, battling for dominance. 17. Generally low humidity will prevail across the Northeast as Canadian high pressure ridges south from Quebec. 18. On the northern rim of the high pressure ridge , several severe long-lived windstorms called derechos formed. 19. Unusually warm weather has thrown up great pressure ridges of ice and opened large areas of water. 20. The farther west the high pressure ridge moves, the more the storm is expected to track west.
