Dec/Jan is the middle of the Antarctic summer with the 'warmest' temperatures. At this period the mountain has a unique combination of very low temperatures and 24 hour daylight. Strong winds and storms are not uncommon.
Vinson (like Denali) is at high latitude and the effects of altitude are greater here than at the same height in the Himalayas.
Wind chill rating: Severe
Vinson is one of the most isolated peaks on earth, where you need full confidence in your gear. At the same time there are strict weight limits on flights into Antarctica, so every bit of weight you can save is worthwhile.