As someone who also gets random urges to do things to her hair (cut it, dye it, dye it outrageous colors), I understand the urge. If you want to do the change, now is the time. Makes it easier to blow dry or air dry so it doesn't freeze or cause you to get a cold while out in the winter weather. And it should be long enough for a ponytail by the time warmer weather returns. Plus you get those weird "who IS that?" moments as you catch your reflection over hte next couple of days.