Our first time visiting South America....late December/early January...two weeks...will be in Santiago, Valpariso, San Pedro de Atacama, and the Lake District! Realize it's summer there but reading indicates evenings can be quite cool in Atacama and it can be rainy in the Lake District. Any suggestions on what clothing to pack? Do we need jackets?

Yes, you need jackets.
Santiago will be hot, dry (around 30C) during the day but it cools off to a pleasant temperature at night.
It is cooler by the sea but should be in the mid-20s centigrade and a bit cooler at night. Early mornings are often misty.
San Pedro de Atacama will be hot during the day but, being in the desert, the temperatures will drop a lot at night. A light fleece and even a couple of layers are necessary.
In the lake district it is usually hot at this time of year, but rain is always possible. I usually take a lightweight waterproof to put on if it rains.
I would bring some sort of pullover sweater, a fleece jacket and a waterproof to cover the lower temperatures, a light sweater or shawl for evenings in Santiago and Valparaíso. Other than that, summer clothes.

Huentetu has confirmed what I am planning on taking. I, too, will be in Santiago and area, and also in the lake district.
I am planning on taking a fleecy jacket and a rain jacket.
My fleecy is a little bit dressy, if you can imagine a fleecy being dressy. It's black, and the fleece is curly. So I can wear it in the evening , if necessary.

Because it will be hot, I've bought a couple of the broomstick cotton long skirts to wear . It doesn't matter if they wrinkle,and they, hopefully will be cool. I'm past the age where I can wear shorts! ..and I think pants will be too hot. I'm taking tshirts and tanks layered with a blouse.
I'm hoping this will do me, and I won't be too hot.

Hope you have a great time. I'll be following right after you.

You are both so very helpful! Thank you! I'll try to do at least a short trip report. We are due back January 7th.

Kodi, what dates will you be in Chile? I ask because the second round of the presidential election is on the 17th. This will interrupt things a bit on that day. I can give you more detail if you will be here then.

just read it in the Wall Street Journal yesterday; I read one thing is that no alcohol is sold on election day.

Yes, that is true. The country is dry from midnight to midnight on election day. This includes hotels and resaturants, of course, but I have seen it relaxed a bit in the evening in tourist spots outside Santiago but don't count on it. Transportation within cities is very crowded as people move around to where they are registered to vote and intercity buses fill up. Many places will be closed until the early afternoon or not open at all. But a lot of tourist services keep going. It depends a bit on where you are.

Huentetu, thank you so much for letting me know. I actually arrive in Santiago on the 17th , mid day. Aside from no alcohol, and crowded buses, is there anything else I need to know? I'll be tired so won't want to do much, but wil want to wander around the city centre to see it.

Any more advice?

Hi there. No, polls usually close about 4 pm give or take. If you take an official taxi from the airport (the desks are inside the customs area just before you emerge into the public areas of the airport and your driver meets you as you exit)the price is fixed and there is no tipping. Should be around US$30 more or less depending on where you are going.
Whoever wins the elections, their fans will be out in the street celebrating. This will make for crowds in some parts of downtown, but I don't think that will get going until 7-8 pm. I am not sure if museums will open after 2 pm (everything has to shut until then) and they are closed Mondays.
If you need a restaurant in the downtown area on a Sunday, the Lastarria street area and the Patio Bellavista in Bellavista are your best bets. Or you might like an early night at your hotel.
http://www.barriolastarria.com/plano..._lastarria.htm
http://www.patiobellavista.cl/patiob...restaurant.php
Any restaurant can call a radio taxi for you to go back to your hotel.

Thank you very much .. at least if I see crowds celebrating, I'll know why !

I doubt if I will want to be fine dining... I'll probably just grab something quick. I'll check out your sites... thanks again. I appreciate the help.