Blood Pressure in high altitude and cold

Patient: Hi, I live in california and often retreat to big bear mountain, 7,000 elevation. My father recently started getting high blood pressure in big bear but only in the winter or when its cold and only when its cold in high elevations. Other than the mixture of elevation and cold he is perfectly fine, only when they are combined does his blood pressure rise, what cures are there for this if any or at least preventions. Thank you