A status yellow snow and ice warning has been issued for 13 counties, lasting until midday on Tuesday.
The warning came into effect at 8pm on Monday for every county in Connacht, along with the counties of Cavan, Donegal, Monaghan, Longford, Louth, Meath, Offaly and Westmeath.
The UK Met Office has issued a snow and ice warning for Antrim, Down, Tyrone and Derry from 5pm on Monday to 11am on Tuesday morning.
There will be a strong north-south split in the weather on Monday with the southern half of the country enjoying spring sunshine and temperatures of up to 12 degrees. By contrast, temperatures in Donegal will struggle to rise above four degrees.
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Monday night will see falls of snow on higher grounds in the north. Temperatures will be between minus 2 and 3 degrees and icy stretches will develop on some untreated roads and paths.
Tuesday will be a cold day everywhere with highest temperatures of 4 to 7 degrees in fresh and gusty northwest winds. Tuesday night will see temperatures from minus 4 to zero degrees.
Rain will develop in the southwest, spreading northwards over the country during Wednesday morning, preceded by sleet or snow for a time in the north.
St Patrick’s Day looks like it will be a mild day with highest temperatures of between 12 and 15 degrees. There will be a mix of sunny spells and showers, some possibly heavy and prolonged.