only ever been to the 2 places in september,in san francisco when you got down to pier 39 area and going across to Alcatraz island the wind made it cool,for winter i would take thick jumper and a fleece or big coat maybe even a Hat,around the union sq bit where you are staying can be very strong winds as well,if you are walking around so you will need to wrap up well,in vegas would say you be ok in the day jeans,maybe a t-shirt etc...but on a night may go a little cold,but im sure someone on the forum been in Jan,give you better advice,From San Fran airport to union SQ,depending on the traffic take about 25-30mins in a taxi...you could catch the Bart rail system from the airport to powell st station,but after a long flight and maybe some luggage for the time of the year you going and your first trip i wouldnt advise,You could also use supershuttle bus service for the round trip they will pick you up for your return journey to the airport if you are flying to vegas.The hilton hotel is lovely hotel on our trips always gone to the bar there right at the top of the hotel for stunning views of the city.taxi price i would say be around $40-45 dollars from the airport but could always check supershuttle website below

http://www.supershuttle.com/

also BART transit website trip takes around 30mins

http://www.bart.gov/index.aspx

we were 5 mins walk from Union Square. Taxi was 35 dollars. We did price up the supershuttle but the difference in price wasn't huge and, as yeltzman said, after a long flight we thought it was worth spending a few dollars more for the taxi

thanks for the replies will look into the links.

From what I've read about Vegas during December and January, it gets very cold, cold enough for winter coat, hat and gloves. Google any of the weather sites and you should be able to get historical temperatures.

luci

I've been to San Francisco in February, where the weather ranged from
sunny t-shirt weather to cold, pouring rain and miserable.

Thanks for replies, better take a mix of clothes i think,

January can be pretty chilly in Vegas, especially at night. Even if it is warm during the day, the temperature drops like a stone when the sun goes down. It has been colder than normal the last few days there. Our friend tells us that it was 15F below the normal high temps for the second half of December.

San Francisco will likely be very chilly and good possibilities for rain. Bring a warm coat and rain protection. By all means, take a cab as it will be worth it after that flight.

Union Square is an excellent location. Central to many things such as Chinatown and Fisherman's Wharf. Shopping immediately around the square is excellent. There is a street car trolley stop there and which you can take all the way down to Fisherman's wharf area. Highly recommended.

Also take some warm clothes for Vegas. Although it is high desert, at night it will cool down dramatically. So a mix of clothes is much recommended.