Weather will likely play an important role when you plan your trip to Lewis Pass, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually February and January with an average temp of 61°F, while the coldest months are July and August with an average of 50°F. The rainiest months in Lewis Pass are May, September, December, and October, with each month seeing an average of 13 inches of rainfall.