June - August
The weather in Halifax can be damp and chilly in the winter, but warms up nicely in July and August, with average temperatures in the low- to mid-20s (Celsius). The city gets plenty of hot days, too, with temperatures rising to the high-20s. That's when everyone visits a local beach or lake, then heads to one of the many bar patios once the sun goes down. There are many festivals in the city through the summer, including the famous Halifax International Busker Festival.
November - March
Halifax can be wet through November, but can also be unpredictably warm and sunny. When it gets cold, temperatures drop below freezing and the city can get fair-sized dumps of snow (but handles them well and everyone carries on as normal). As long as you wrap up warm, you’ll still get to experience most of what the city has to offer, as nothing shuts down, really, except the overtly summery stuff.
April - May, September - October
These are still good times to visit Halifax. You’re likely to have sunshine and good weather throughout (though you should pack an umbrella and a sweater, for sure). Everything is open during these times, and because the universities are in session, the city will be fun and extra-vibrant.