I'm not sure what you mean by a day trip being enough time to do Normandy; Normandy covers a very large area. If you mean the D-Day Beach sites, then I would wait until warmer weather to do that and/or Mont St. Michel. I visited that area a few years ago in May, and it was cold, rainy, and blustery even then. Also, I would recommend staying a night or two to adequately see the WW II sites; Bayeux makes a great base for touring that area.

The trip to Mont St-Michel is a long one, and days will be short in December. You would really need to do an overnight trip or save it for spring/fall (the Mont is mobbed in summer).

Why not take the TGV to Strasbourg and have a fine time at the Christmas market?

Normandy is a vast region starting just outside Paris (Monet's house in Giverny is in Normandy) and stretching as far as Mont Saint Michel, which is also in Normandy. In my opinion Mont St Michel is too far for a day trip especially in winter as it's a 4-hour ride each way.

If by Normandy you mean the American D-Day beaches (as you seem to be American and you wouldn't have time for the other ones anyway), they're over 3 hours away so while feasable in a day it's still a bit far in winter with limited daylight. The amount of time you'd have there would only allow for a short visit to Omaha Beach and the American Cemetery. It is certainly possible but you'd spend twice as much time on the bus there and back as you would touring that one site.

I agree with the other posters that you really need an overnight trip for either site at any time of the year, even more so in winter with daylight from 8:30 to 5 pm.

We are also visiting Paris in December and thought we wanted to go to Normandy for a day or two to see the D-Day sites. After looking at the potential weather and other factors we decided to delay the Normandy visit to sprintime and plan to stay in Bayeux for several days and base our travels from there.

www.chartres-tourisme.com

far closer better easier quick train

and spectacularly festive this time of year...

eurocheapo.com/paris great city guide tips

There are bus tours, at least in summer, to the Normandy beaches. LONG LONG day. Mont st. Michel is even further.
I've been to Paris many times, and 3 days is STILL not long enough to leave it!! Just my opinion.

Have you been to Versailles, Chartres? Both are close by and well worth the visit. In December, with the iffy weather and short days, you are better off planning something close by. With 3 days, I would stay in Paris which is beautiful at the holidays. After 8 trips we always find something new to see and do.

Although it was fun walking around Mont St. Michel during the day, to us the highlight of seeing it was watching the lights come on at night with the backdrop of a beautiful sunset. Not only would it be pretty cold to stand out on that causeway for 2 hours in winter, but the timing wouldn't work for a day trip.

I recommend taking the advice given above and plan your Normandy trip for 5 days in the late spring sometime.

honestly, if you have only got 3 days in Paris in December with very short day lengths, i would not commit yourself to any pre-booked tours, that you might decide you don't want to do when you get there.

you can easily decide to do Versailles or Rouen or Chartres [or St. Germain-en-Laye] when you are there.

Yes, Rouen! It's the capital of upper Normandy, and there is lots to see there. We were blown away by the Gothic churches. There are three in close proximity, the cathedral, Saint-Ouen and Saint-Maclou. Then there's the old clock, the site where Joan of Arc was burnt, the art museum, etc. So plenty to see in not so great weather.