Usually, winter comes as a surprise to Bulgaria's biggest town.
This is the standard explanation that the City Council folk give when there is over in inch of snow and the traffic, especially away from the main roads, gets completely paralysed. When this happens, don't drive!
Take a walk in the snow-covered streets and you will discover a completely new, and very enchanting, city. Everything will be enveloped in white and you can spend hours taking in buildings and people you've looked at before but will now be seeing for the first time.
Where in Bulgaria are you?