SF is a wonderful place but it is not the place to go for warm weather at any time of year. It's pretty much always sweater weather here, with the occasional 70 degree day in Sept or Oct. Summers are particularly cold in the city because of the wind and fog that whips through the Golden Gate. It will often be 40-50 in the city and 100+ in the valleys just 40 miles away. The spring and fall are a bit better, but you can never rely on any particular day to be warm enough to leave the jacket at home. February can range from 40 to mid-60's, depending on whether it's raining or sunny. Of course, all of this is relative if you live in the midwest. 40-50 may not seem cold at all compared to what happens elsewhere in the country but it will likely be disappointing to someone looking for a warm weather escape.