“There is a slight chance that some rural communities could become cut off,” the Met Office said in its latest warning, external.
There is also a small chance of cuts to power and mobile service, it added, with strong winds forecast.
People living in higher ground in mid and southeast Wales could see up to 20cm (8in) of snow.
The counties affected by the yellow warnings include Blaenau Gwent, Bridgend, Caerphilly, Carmarthenshire, Ceredigion, Conwy, Denbighshire, Gwynedd, Merthyr Tydfil, Monmouthshire, Neath Port Talbot, Newport, Pembrokeshire, Powys, Rhondda Cynon Taf, Swansea, Torfaen and Wrexham.
