Wales could see "significant flooding" and travel disruption due to spells of prolonged and heavy rain brought by Storm Christoph this week.
The Met Office named the storm after issuing yellow weather warnings for much of the UK from Tuesday until midday on Thursday.
Flooding of homes and businesses is likely, and bus and train services will probably be affected with journey times taking longer, according to the forecast.
The Met Office also said there could be some interruption to power supplies and other services.
Most parts of Wales could see up to 60 millimetres (mm) of rain, with hills in the north seeing up to 200 mm.
Natural Resources Wales has issued a flood alert for areas near south Pembrokeshire rivers from Monday, with persistent and heavy rain continuing throughout the week.
Other areas of the UK were hit by more snow over the weekend, with people in eastern England seeing up to eight centimetres on Saturday.
Heavy rainfall combined with some snowmelt is expected to bring flooding in northern areas of England, including Manchester, Leeds and the Peak District, from Tuesday morning.
What to do before a flood:
Move family, pets and valuables to a safe place
Turn off gas, electricity and water supplies if it is safe to do so
Put flood protection equipment in place
Farmers should consider moving livestock and equipment away from areas likely to flood
Avoid walking, cycling or driving through flood water
Analysis from ITV Wales Weather Presenter Ruth Dodsworth
You know you're headed for trouble when the Met Office officially names a storm, and today they have done exactly that.
Storm Christoph, the third named storm of the autumn/winter season will make his presence felt here in Wales between Tuesday and Thursday of this week.
And he promises to bring some significant disruption across the country.
The expected rainfall totals are quite staggering. For the whole of Wales, the average rainfall total we would expect to see during the whole month of January is around 157 mm.
Between Tuesday and Thursday, some parts of north Wales (Capel Curig, Snowdonia) could see over 200 mm falling - that's well over a month's worth.
Across the hills and mountains of Wales in general (Brecon Beacons, Cambrians) we could see up to 100 mm - about two thirds of a month's worth, and at lower levels across Wales we could see between 30-50 mm, around a third of a month's rainfall.
So should we be worried? Well, frankly, yes.
Localised flooding is a real risk, with Natural Resources Wales monitoring flood levels. Their website is updated every 15 minutes, or there is a Floodline number you can call, which is open 24 hours a day.
All of this with a strong, gusty wind just to compound matters. And a northerly airflow will return through Wednesday, which means some of this rainfall could turn to snow over the hills through Wednesday night, with up to 10 cm possible over Snowdonia for example.
The Met Office only names a storm if it's deemed to be impactful. And Storm Christoph certainly guarantees to keep us on our toes. As ever, stay warm and stay safe.