Great question. I’ve day-hiked it many times(going again in 2 weeks) and I never believe what the forecast says. I always prepare for the worst: balaclava, gore Tex gloves, waterproof pants, and a good down jacket. Wind chill temperatures can be 50-60 degrees colder on top compared to the portal.
The items I mentioned are extremely light and can be life-saving.
On the day you’re going: 45 Mph winds and a wind chill of 19 degrees is forecasted. Just be prepared. Oh, I never use a bladder in freezing temps. The hose freezes up. Have water bottles and stuff them in your puffer jacket.
Good luck and have a safe trip!