Forecasters expect a band of patchy mist and fog to smother areas in the south and east of the UK.
Southern England and east Wales will bear the brunt of the bad weather during the early hours of Thursday.
Meanwhile, a covering of cloud strikes the far north, resulting in an outbreak of rain across Northern Ireland.
It is going to be a little bit hazy across some northern parts of the UK this Valentine’s Day, with visibility less than 100 metres.
Meteorologist Carol Kirkwood reported the BBC Breakfast weather forecast live from the London Coliseum today.
She told viewers: “I can tell you it is pretty nippy up here and it’s not just cold in London. It’s cold across many parts of England and so Wales this morning.
“So if you’re heading out you might encounter some frost and the other thing to watch out for this morning is some dense fog.”
Despite the unpleasant conditions in parts of the UK today, Thursday is set to be a day brimming with sunshine and clear skies.
The more direct the sunshine is the bluer skies, with warmest conditions across England and Wales.
Temperatures to reach 14 degrees Celsius in some places and it is possible the heat value could hit 15 degrees Celsius around the Moray Firth.
Nearby weather fronts will be kept at bay by an area of high pressure sitting to the south east of the UK.
The southwesterly breeze continues today and into Friday, though they will be lighter.
Britons can look forward to more sunshine tomorrow, although there will be some mist and fog first thing.
But there will be a change in weather, particularly in the northwest of the UK, where cloud and rain will arrive.
Given the UK has achieved above-average temperatures for this season it is unsurprising bookmaker Coral predicts this Valentine’s Day to be the hottest ever.
Coral make it just 6-4 (from 4-1) February 14 goes down in history as the warmest ever. The record for the hottest Feast of Saint Valentine currently stands at 19.1C.
“It’s going to be one of the hottest Valentine’s Day that we have ever seen in the UK,” Coral’s spokesman Harry Aitkenhead said.
“[There are] mild temperatures up and down the country thanks to a warm front coming in from the Azores.”
He continued: “We’ve slashed our odds this week on Thursday breaking the record and all eyes will be on the thermometers as Valentine’s Day heats up, with it a real possibility.”
BBC Breakfast airs weekdays on BBC One at 6am.