We saw a sunny start to the week but below average temperatures will replace the milder weather of recent days, forecasters say.
Temperatures are set to take a tumble for Tuesday, with maximum temperatures set for around 12C or 13C, which is around average for this time of year.
Temperatures will be "noticeably cooler" this week as Arctic air brings wintry weather to British springtime.
Met Officer forecaster Bonnie Diamond said: "Because it's from an Arctic source, it's going to introduce cooler temperatures to the country as we go through Tuesday and into Wednesday."
Forecasters at the Weather Channel say the chill is caused by high pressure close to Scandinavia pulling cooler air from the east.
Although it is too late in the year for a widespread wintry blast, most places could be vulnerable to overnight frosts.
Weather forecast for Tuesday
Met Office forecasters say there will be a cloudy start in the south with further rain.
It's set to be rather unsettled on Tuesday for much of south Wales with mostly cloudy skies and some outbreaks of rain or drizzle, mostly quite light and patchy, according to BBC forecasters.
It will be drier and brighter in the north with some sunshine, the Met Office say. The brighter weather will then spread further south during the afternoon.
Wednesday and the rest of the week
On Wednesday we'll see sunny spells and drier weather, but a little cooler.
Ms Diamond at the Met Office said clear skies at night will result in a widespread frost from Wednesday.
It'll be "settled and largely dry throughout the remainder of the week", with a mix of cloudy skies and sunny spells, Met Office forecasters say. It'll feel "cold, with nighttime frosts likely."
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