There is a snow and ice warning in effect across the country.
Met Éireann has a status yellow alert in place for wintry showers, which could lead to up to 3cm of snow during today and tomorrow.
The warning is in place from 6am today until 11pm tomorrow.
The west and north, as well as high ground, are expected to see the largest accumulations. It will be very cold and windy, with widespread rain to begin, turning to sleet and snow over parts of Ulster.
Brian Farrell from the Road Safety Authority said it is important to defrost windows and to remove snow from cars before setting out on a journey.
"You must make sure the vehicle is fit for purpose," he said. "Before setting out, you must make sure the windows are de-misted, that you clear the ice off the windows using a screen-scraper rather than boiling water as (the water) could crack the glass.
"Gently does it is the key - easy on the braking and easy on the acceleration."
It will become drier for a time with sunny spells developing later today, but wintry showers are due to push down across the country again in a strong to gale force west to northwest wind.
Highest temperatures are due to be just -2C to -5C, and it will be coldest further north.
There will be scattered sleet and snow showers tonight. It will stay windy in a strong and gusty westerly wind, with the risk of thunder. Frost and ice is expected in parts. Temperatures of -1C to +2C are expected, and it will be coldest across Ulster.