The Cascade Mountains to the west and the Blue Mountains to the east have a considerable influence on this area. Also, down slope foehn type winds are not uncommon during the fire season. The Columbia River Gorge frequently causes strong channeling of westerly winds into the area after a cold front passage, but with little rainfall. Flashy range fires often occur in this area as a result from either lightning, or anthropogenic causes, and frequently spread very rapidly. This zone has the largest variability in terrain ranging from mountains with steep slopes, and narrow canyons to high elevation rolling hills, grasslands, meadows, and river valleys.
Weather conditions can vary widely and are influenced by the terrain on a diurnal basis.
Annual precipitation amounts range from near 10 inches on the grasslands to near 35 inches in the Ochoco mountains, with the majority of the precipitation occurring during the winter months. Heavy fuel loadings and the availability of ladder fuels in the higher elevations, give this area the potential to develop large, crowning project fires resulting from the combination of dry lightning, gusty winds, and prolonged drought. Terrain in this area is highly variable and complex, ranging from high mountains, steep slopes, and narrow canyons to flat plateaus, meadows, and wide river valleys. Weather conditions vary widely and are largely influenced by the terrain on a diurnal basis. Annual precipitation amounts range from under 20 inches in some valleys to over 50 inches in the highest mountains, with the majority of the precipitation occurring during the winter months.