Arriving in San Francisco on Thurs - July 22nd. What is the predicted weather? Do I need a light jacket for evenings? I'm from NY and could use some advice. Thanks.

You will need a jacket in the evening. You may even need one in the day depending on the nature of the fog and wind when you are there.
The predicted high is mid 60s. The hotter it is in the central valley the more likely fog will be present.

The weather in SF in the summer can be quite unpredictable. We've had some lovely sunny days the past few weeks and some quite chilly, foggy, windy ones lately. Today was the latter sort, darn it. A couple of weeks ago I hauled out my knee-length wool winter coat to wear one evening, I was so cold.! This evening I wore a down vest when I went out for a walk as it turned dark. I would advise you to bring layers so you can deal with the variable conditions.

Are you going to be in the city the whole time? If you head out of the city, in any direction, less than 30 minutes away, it can be more than 30 degrees warmer, so then you need to be prepared for heat. Although usually not humidity at least.

Definitely be prepared for the possibility of cold (not cool) weather. One August a few years ago we cut our SF visit short because it was cold there and 20 degrees warmer a few miles away to the south, east, and north.

HTTY

I am wearing a light jacket today, and I'm the type that's usually warm. Pack so you can have layers: t-shirt, light sweater, windbreaker - so you are ready for any unpredictable weather. Even walking on different sides of the same street: sunny or shady will require different layers.

This morning, it's cold to me (not cool), but that depends on your definition. I've lived in California a long time, and 56 °F is cold to me. The high temp. today is only expected to be 58 °F . (Confirming what others have said, where I live, which is 16 miles from downtown SF, it's expected to be 70 °F today, and last weekend, it was close to 90).

Summer in SF tends to be September - not July. I would never go there without at least a light jacket and some long-sleeve tops

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Me either, and I live here! Actually, June-August, the weather is totally hit-or-miss, one day 80, the next 62. September is more consistently nice.