28-30 grains is a good starting point. You need to have enough powder to get a tight pack when you ram the ball down....otherwise, you'll likely experience hang fires.
I speculate your lube will be on the "extra" stiff side when you get out into the weather.
Under 40 F I recomend straight Crisco or store-brand equivilent.
Save the thicker blend for summer use.
Slim