4-season tents–the truly Everest-worthy varieties–are definitely overkill for the AT.
But all 3-season tents are not created equally. If it is your intention to NOT use shelters, or you are in a big push of thru-hikers when shelters are likely to be crowded, you will want to choose a tent that can better withstand some snow and wind.
My experience has been that 3-season hoop tents with steeper sides tend to shed snow better than other designs. The SD Clip Flashlight is an example of such design, but there are others (I only mention this model to give you something to google so you can see what it looks like). If you bring and use extra guy-out points in heavy wind conditions, these types of tents are fairly sturdy too.
However, by today’s standards, these tents are not considered “ultralight.” Expect to carry at least 4 lbs. if you choose a tent like this.
Of course if you’re measuring wet, heavy snow in feet–you’re going to want one of those big bombproof expedition tents. But you’re not going to want to pay for one nor carry the weight of one, so you’ll be heading for shelters or the nearest town when such conditions are forecasted or present. Fortunately, you can often choose to do either on the AT.
Skyline