Weather in San Francisco can vary depending on where you are in the city. The Castro is almost in the middle of the northern neighborhoods. You can expect it to be fairly mild year-round but subject to morning fog and a bit more rain in November through March as the weather comes off the ocean.
Market Street, which runs almost through the middle of the neighborhood, is the main street where you will find more of a metro retail and restaurant feel. This is a major road, so observe pedestrian traffic laws and keep your furry friend on a short leash. On either side of Market Street, you will find the more residential parts of the neighborhood. This is your typical sidewalk experience with an inconsistent number of treescapes to be found in the front yards of homes or along the sidewalks. Make sure both you and your pup are prepared for extended exposure to the sun.
Corona Heights Park is at the north end of the neighborhood. This rustic park with amazing views of San Francisco hosts trails and a dog play area as well. The trails are natural dirt paths with a few concrete steps. This is mostly a uphill, downhill walk. Do be prepared to keep your pup on a shorter leash on the trails. This park is known to have a lot of poison oak which can be transferred to humans via the oils on your pup's hair, so exercise caution around unfamiliar plants.
One more popular park is Mission Dolores Park at 19th and Dolores. It is a popular 16-acre destination park.