Bathroom sink main floor gurgle when toilet flushed

[daysofplumbing]

In the spring summer and fall the bathroom sink does not gurgle but in the winter time it does. Any idea why this would be?

 

[voletl]

Snow or ice blocking the vent

 

[Geofd]

not sure we're you live but I'm thinking its cold in the winter
If that's the only bath int the house that acts like that
I'm guessing that vent isn't high enough above snow/ freeze
level condensation builds up from warm air from vent+cold
air+snow may cause it to freeze over

if the vent is short just extend it you could also add a coupling to
increase the end of the vent

 

[daysofplumbing]

I have another toilet upstairs and no issue. Only main level one. And only in the winter. Strange