Met Eireann says the lowest temperature recorded so far overnight was minus 8.2 degrees in Mountdillon in Co Roscommon.
A low of minus 8.1 degrees was recorded in Athenry in Co. Galway, and it dipped to minus 7.6 degrees in Gurteen, Co Tipperary.
The lowest temperature at Dublin Airport overnight was minus 4.1 degrees.
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A status Orange warning is in place for 19 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 and minus 8 degrees again tonight.
