Brno occupies a pleasant spot between Southern Moravian lowlands and the Bohemian-Moravian Hills, which gives this area a pleasant, fairly moderate climate. Weather here is very similar to the one in Prague.
If you don’t like rain, don’t come here, however. Every single month sees rain on average, with the driest month (March) still bringing an average of 8 wet days. Otherwise, weather here is fairly moderate.
In the winter months, temperatures can drop below freezing at night but rarely during the day (though January’s average high temperature sits about 1 degree Celsius, or about 34 degrees Fahrenheit). During these cold winters months you’ll only see perhaps 2-3 hours of sunlight per day as well.
If you like to travel in the summertime, this is a good time to visit Brno. Some attractions throughout the Czech Republic, and Brno in particular, are only open during the summer months, so this can be a particularly good time to make a visit here.
High temperatures in Brno in June, July and August hover around 78 degrees, but July and August bring with them a fair amount of humidity as well. Be sure to carry a bottle of water with you if you plan to be exploring the city by foot.