A level 3 is declared when average temperatures have, or are about to, fall to 2C and widespread ice and heavy snow is present.
The yellow warning for snow and ice has been issued across Lancashire for today (Friday, January, 16).
Frank Saunders, Chief Meteorologist at the Met Office, said: “After less cold conditions overnight Wednesday and for a time on Thursday, increasingly cold air will spread from the northwest across England on Thursday night and during Friday, with showers turning more wintry from the north.
“Average temperatures are expected to continue falling through the weekend, with a northerly airstream likely to be established by Sunday.
“Frost and ice are expected to become increasingly widespread through the period, with some severe overnight frosts likely in the north over any snow cover by Monday.”
Because of the warnings Public Health England is reminding people to look out for others, to keep warm indoors and to take care when walking on icy or wet surfaces when out and about.
Dr Angie Bone of the extreme events team at Public Health England, said: “Cold does kill, even in places where the temperatures aren’t at their lowest.
“Most of our advice on keeping warm in cold weather may seem like common sense, but it’s important that we make the point that people should think about how cold can affect them.
“Our advice is that when indoors, have plenty of warm food and drinks to stay warm and try to maintain indoor temperatures to at least 18C, particularly if you are not mobile, have long term illness or are 65 or over.”