As sub-zero temperatures swept across Northern Ireland overnight, warnings are in place for drivers to take care on roads.
Monday was a bitterly cold evening, with snow and ice taking hold from late afternoon.
The north west has been particularly badly hit.
Police in Derry said they dealt with 19 crashes in the city as well as city, Strabane, Slaughtmanus and Donemana.
"If you are driving, please slow down and keep a safe distance from the vehicle in front of you," police said.
A number of schools have also been closed.
Bready Jubilee Primary School, 12 Cloughbuoy Road, BT82 0DN
St Canice's Primary School, Feeny, 34 Glenedra Road, BT47 4TW
St Mary's Primary School Claudy, 70 Monadore Road, BT47 4DP
St Brigid's Primary School, Carnhill Estate, BT48 8DU
Gaelscoil Leim an Mhadaidh, 57 Church Street, BT49 0BX
The Academy Nursery School, Londonderry
St Patrick's PS, Pennyburn, Londonderry
Long Tower Primary School, Londonderry
The winter weather snap is expected to continue throughout Tuesday, with further snow showers expected.
A yellow weather warning is expected to remain in place until noon.
Disruption is expected to a number of services, including bin collections.
Derry City and Strabane Council has warned that the "adverse weather conditions" may cause "some disruption to its bin collection services".
It's advising residents to leave their bin out for collection as normal, "however for those whose bins are not emptied today please be advised that it will be emptied as conditions improve later in the week".
The council said the move was in the "interest of health and safety for both our crews and the general public".
It added: "The public are also advised that all Council cemeteries will be closed to the public today with the exception to facilitate burials which will go ahead as normal."
Meanwhile the council said "recycling centres and parks will be opened when it is safe to do so".
The Police Service of Northern Ireland (PSNI) that there is a "risk of snow and ice on the roads" this morning.
It advised motorists to "please reduce your speed and drive with extra caution".
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