Forecasters previously warned of a “small chance” of snow settling with disruption to road, rail and air services, as well as interruptions to power supplies and other utilities towards the end of this week.
However, snow fall is now considered “likely” across south east England and East Anglia, while associated heavy rain and strong winds may prove additional hazards.
As skies clear on Thursday night and temperatures drop, there is also potential for widespread ice to form quite rapidly on untreated surfaces.
A Met Office spokesman said: “As a developing area of low pressure moves east across southern Britain on Thursday there is potential for rain to turn rapidly to snow as cold air is drawn in.
“However, there is a great deal of uncertainty over the track and intensity of this system, meaning that confidence is low in the amount and extent of any snow. “