The Met Office warning is in force from 4am until 8pm and covers all six counties, with unsettled conditions expected to move slowly eastwards during the day before easing later in the evening.
According to the forecaster, periods of rain will fall as snow over higher ground, while strong southeasterly winds may gust between 45mph and 55mph in places, particularly during the morning hours.
The Met Office said the combination of wet weather, wintry precipitation on hills and gusty winds could result in difficult travelling conditions, longer journey times and some disruption to road and public transport services.
More broadly, the unsettled conditions form part of a changeable weather pattern affecting the UK this week, with Atlantic systems bringing spells of rain, wind and occasional snow, especially across northern and western areas.
Motorists are being advised to take extra care on the roads, particularly in exposed areas and higher routes where wintry conditions may develop, and to check the latest forecasts before travelling.