Met Éireann says the lowest temperature recorded so far overnight was minus 8.2 degrees in Mountdillon in Co Roscommon while it dipped to minus 7.6 degrees at the weather station in Gurteen in Tipp.
A status Orange warning is in place for Tipperary and 18 other counties until midday today, with another orange alert coming into effect from 6pm for all counties bar Co Donegal.
Temperatures are expected to fall to minus 7 or 8 degrees again tonight.
The Road Safety Authority is reminding drivers to take extra care and keep a safe distance from the vehicle in front.
