I live in Sarajevo so my weather information is mainly based on that area of BiH.  We have been here since October, 2005.  To me, Sarajevo weather is much like Washington, DC., USA.  For example, we have 4 seasons.  I have experienced fall which has cool nights and warm 70-80 degree, sunny days.  So pack umbrellas, and light jackets.  Winter brings snow and grey, grey skies.  Pack warm clothes as it tends to be a damp cold.  Bring snow boots or at least some water repellent foot ware.   Sarajevo is situated between mountains so during the winter we have lots of fog so flights into SJJ airport are often delayed.  Keep that in mind when booking connecting flights.  Snow falls seemed to max out at 10 inches, with not too much accumulation past that.  (I did hear Winter 2004 brought  some days of consecutive 3 foot snow falls and even snow in June.)  But if you can get here, I heard the skiing is great.  The 1984 winter Olympics were held in Sarajevo.  We are in spring now (it is May 24, 2006).   Temperatures are in the low to mid 80s during the day and mid 50s at night.  Sun is out!  I love colder weather so the coolness of April was very enjoyable, however April seemed to be a very rainy month.  So for sightseeing be advised. 

I will try and update this weather report once I have experienced summer in Sarajevo.   I have heard that most of Europe goes on vacation in August so hotel rooms are hard to find.  I am not sure if that includes BiH.  I have heard the Croatian coast really fills up with tourists (which is not particularly when I want to travel!)