Average annual precipitation is 15 inches (380 mm), but great variations are seen. The mountain ranges block the moist Pacific air, holding moisture in the western valleys, and creating rain shadows to the east. Heron, in the west, receives the most precipitation, 34.70 inches (881 mm). On the eastern (leeward) side of a mountain range, the valleys are much drier; Lonepine averages 11.45 inches (291 mm), and Deer Lodge 11.00 inches (279 mm) of precipitation. The mountains themselves can receive over 100 inches (2,500 mm), for example the Grinnell Glacier in Glacier National Park gets 105 inches (2,700 mm). An area southwest of Belfry averaged only 6.59 inches (167 mm) over a sixteen-year period. Most of the larger cities get 30 to 50 inches or 0.76 to 1.27 metres of snow each year. Mountain ranges themselves can accumulate 300 inches or 7.62 metres of snow during a winter. Heavy snowstorms may occur any time from September through May, though most snow falls from November to March.