Well, this is what Wikipedia has to say about Idaho's climate:
Quote:
Climate
Idaho has much variation in its climate. Although the state's western border is located about 350 miles (560 km) from the Pacific Ocean, the maritime influence is still felt in Idaho, especially in the winter when cloud cover, humidity, and precipitation are at their highest points. This influence has a moderating effect in the winter where temperatures are not as low as would otherwise be expected for a northern state with a mostly elevated altitude.[14] The maritime influence is lowest in the southeastern part of the state where the precipitation patterns are often reversed, with wetter summers and drier winters, and seasonal temperature differences more extreme, showing a more continental climate.
Climate in Idaho can be hot, although extended periods over 100 °F (38 °C) for the maximum temperature are rare, except for the lowest point in elevation, Lewiston, which correspondingly sees very little snow. Hot summer days are tempered by the low relative humidity and cooler evenings during summer months since, for most of the state, the highest diurnal difference in temperature is often in the summer. Winters can be cold, although extended periods of bitter cold weather below zero are unusual. This is what led the railroad tycoon Harriman family to develop the most famous ski resort, Sun Valley.